Transactional isolation for /sync (#2745)

This should transactional snapshot isolation for `/sync` etc requests.

For now we don't use repeatable read due to some odd test failures with
invites.

syncapi/consumers/clientapi.go

@@ -34,6 +34,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
@@ -46,7 +47,7 @@ type OutputClientDataConsumer struct {
 	topic        string
 	topicReIndex string
 	db           storage.Database
-	stream       types.StreamProvider
+	stream       streams.StreamProvider
 	notifier     *notifier.Notifier
 	serverName   gomatrixserverlib.ServerName
 	fts          *fulltext.Search
@@ -61,7 +62,7 @@ func NewOutputClientDataConsumer(
 	nats *nats.Conn,
 	store storage.Database,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 	fts *fulltext.Search,
 ) *OutputClientDataConsumer {
 	return &OutputClientDataConsumer{

syncapi/consumers/keychange.go

@@ -26,6 +26,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/nats-io/nats.go"
@@ -40,7 +41,7 @@ type OutputKeyChangeEventConsumer struct {
 	topic      string
 	db         storage.Database
 	notifier   *notifier.Notifier
-	stream     types.StreamProvider
+	stream     streams.StreamProvider
 	serverName gomatrixserverlib.ServerName // our server name
 	rsAPI      roomserverAPI.SyncRoomserverAPI
 }
@@ -55,7 +56,7 @@ func NewOutputKeyChangeEventConsumer(
 	rsAPI roomserverAPI.SyncRoomserverAPI,
 	store storage.Database,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 ) *OutputKeyChangeEventConsumer {
 	s := &OutputKeyChangeEventConsumer{
 		ctx:        process.Context(),

syncapi/consumers/presence.go

@@ -23,6 +23,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -39,7 +40,7 @@ type PresenceConsumer struct {
 	requestTopic  string
 	presenceTopic string
 	db            storage.Database
-	stream        types.StreamProvider
+	stream        streams.StreamProvider
 	notifier      *notifier.Notifier
 	deviceAPI     api.SyncUserAPI
 	cfg           *config.SyncAPI
@@ -54,7 +55,7 @@ func NewPresenceConsumer(
 	nats *nats.Conn,
 	db storage.Database,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 	deviceAPI api.SyncUserAPI,
 ) *PresenceConsumer {
 	return &PresenceConsumer{

syncapi/consumers/receipts.go

@@ -28,6 +28,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
@@ -38,7 +39,7 @@ type OutputReceiptEventConsumer struct {
 	durable    string
 	topic      string
 	db         storage.Database
-	stream     types.StreamProvider
+	stream     streams.StreamProvider
 	notifier   *notifier.Notifier
 	serverName gomatrixserverlib.ServerName
 }
@@ -51,7 +52,7 @@ func NewOutputReceiptEventConsumer(
 	js nats.JetStreamContext,
 	store storage.Database,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 ) *OutputReceiptEventConsumer {
 	return &OutputReceiptEventConsumer{
 		ctx:        process.Context(),

syncapi/consumers/roomserver.go

@@ -33,6 +33,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
@@ -45,8 +46,8 @@ type OutputRoomEventConsumer struct {
 	durable      string
 	topic        string
 	db           storage.Database
-	pduStream    types.StreamProvider
+	pduStream    streams.StreamProvider
-	inviteStream types.StreamProvider
+	inviteStream streams.StreamProvider
 	notifier     *notifier.Notifier
 	fts          *fulltext.Search
 }
@@ -58,8 +59,8 @@ func NewOutputRoomEventConsumer(
 	js nats.JetStreamContext,
 	store storage.Database,
 	notifier *notifier.Notifier,
-	pduStream types.StreamProvider,
+	pduStream streams.StreamProvider,
-	inviteStream types.StreamProvider,
+	inviteStream streams.StreamProvider,
 	rsAPI api.SyncRoomserverAPI,
 	fts *fulltext.Search,
 ) *OutputRoomEventConsumer {
@@ -449,8 +450,14 @@ func (s *OutputRoomEventConsumer) updateStateEvent(event *gomatrixserverlib.Head
 	}
 	stateKey := *event.StateKey()
 
-	prevEvent, err := s.db.GetStateEvent(
+	snapshot, err := s.db.NewDatabaseSnapshot(s.ctx)
-		context.TODO(), event.RoomID(), event.Type(), stateKey,
+	if err != nil {
+		return nil, err
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+
+	prevEvent, err := snapshot.GetStateEvent(
+		s.ctx, event.RoomID(), event.Type(), stateKey,
 	)
 	if err != nil {
 		return event, err

syncapi/consumers/sendtodevice.go

@@ -31,6 +31,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
@@ -43,7 +44,7 @@ type OutputSendToDeviceEventConsumer struct {
 	db         storage.Database
 	keyAPI     keyapi.SyncKeyAPI
 	serverName gomatrixserverlib.ServerName // our server name
-	stream     types.StreamProvider
+	stream     streams.StreamProvider
 	notifier   *notifier.Notifier
 }
 
@@ -56,7 +57,7 @@ func NewOutputSendToDeviceEventConsumer(
 	store storage.Database,
 	keyAPI keyapi.SyncKeyAPI,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 ) *OutputSendToDeviceEventConsumer {
 	return &OutputSendToDeviceEventConsumer{
 		ctx:        process.Context(),

syncapi/consumers/typing.go

@@ -24,6 +24,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/jetstream"
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/nats-io/nats.go"
 	log "github.com/sirupsen/logrus"
@@ -36,7 +37,7 @@ type OutputTypingEventConsumer struct {
 	durable   string
 	topic     string
 	eduCache  *caching.EDUCache
-	stream    types.StreamProvider
+	stream    streams.StreamProvider
 	notifier  *notifier.Notifier
 }
 
@@ -48,7 +49,7 @@ func NewOutputTypingEventConsumer(
 	js nats.JetStreamContext,
 	eduCache *caching.EDUCache,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 ) *OutputTypingEventConsumer {
 	return &OutputTypingEventConsumer{
 		ctx:       process.Context(),

syncapi/consumers/userapi.go

@@ -28,6 +28,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/streams"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
@@ -40,7 +41,7 @@ type OutputNotificationDataConsumer struct {
 	topic     string
 	db        storage.Database
 	notifier  *notifier.Notifier
-	stream    types.StreamProvider
+	stream    streams.StreamProvider
 }
 
 // NewOutputNotificationDataConsumer creates a new consumer. Call
@@ -51,7 +52,7 @@ func NewOutputNotificationDataConsumer(
 	js nats.JetStreamContext,
 	store storage.Database,
 	notifier *notifier.Notifier,
-	stream types.StreamProvider,
+	stream streams.StreamProvider,
 ) *OutputNotificationDataConsumer {
 	s := &OutputNotificationDataConsumer{
 		ctx:       process.Context(),

syncapi/internal/history_visibility.go

@@ -100,7 +100,7 @@ func (ev eventVisibility) allowed() (allowed bool) {
 // Returns the filtered events and an error, if any.
 func ApplyHistoryVisibilityFilter(
 	ctx context.Context,
-	syncDB storage.Database,
+	syncDB storage.DatabaseTransaction,
 	rsAPI api.SyncRoomserverAPI,
 	events []*gomatrixserverlib.HeaderedEvent,
 	alwaysIncludeEventIDs map[string]struct{},

syncapi/notifier/notifier.go

@@ -318,13 +318,20 @@ func (n *Notifier) GetListener(req types.SyncRequest) UserDeviceStreamListener {
 func (n *Notifier) Load(ctx context.Context, db storage.Database) error {
 	n.lock.Lock()
 	defer n.lock.Unlock()
-	roomToUsers, err := db.AllJoinedUsersInRooms(ctx)
+
+	snapshot, err := db.NewDatabaseSnapshot(ctx)
+	if err != nil {
+		return err
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+
+	roomToUsers, err := snapshot.AllJoinedUsersInRooms(ctx)
 	if err != nil {
 		return err
 	}
 	n.setUsersJoinedToRooms(roomToUsers)
 
-	roomToPeekingDevices, err := db.AllPeekingDevicesInRooms(ctx)
+	roomToPeekingDevices, err := snapshot.AllPeekingDevicesInRooms(ctx)
 	if err != nil {
 		return err
 	}
@@ -338,7 +345,13 @@ func (n *Notifier) LoadRooms(ctx context.Context, db storage.Database, roomIDs [
 	n.lock.Lock()
 	defer n.lock.Unlock()
 
-	roomToUsers, err := db.AllJoinedUsersInRoom(ctx, roomIDs)
+	snapshot, err := db.NewDatabaseSnapshot(ctx)
+	if err != nil {
+		return err
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+
+	roomToUsers, err := snapshot.AllJoinedUsersInRoom(ctx, roomIDs)
 	if err != nil {
 		return err
 	}

syncapi/routing/context.go

@@ -51,6 +51,12 @@ func Context(
 	roomID, eventID string,
 	lazyLoadCache caching.LazyLoadCache,
 ) util.JSONResponse {
+	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
+	if err != nil {
+		return jsonerror.InternalServerError()
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+
 	filter, err := parseRoomEventFilter(req)
 	if err != nil {
 		errMsg := ""
@@ -97,7 +103,7 @@ func Context(
 		ContainsURL:             filter.ContainsURL,
 	}
 
-	id, requestedEvent, err := syncDB.SelectContextEvent(ctx, roomID, eventID)
+	id, requestedEvent, err := snapshot.SelectContextEvent(ctx, roomID, eventID)
 	if err != nil {
 		if err == sql.ErrNoRows {
 			return util.JSONResponse{
@@ -111,7 +117,7 @@ func Context(
 
 	// verify the user is allowed to see the context for this room/event
 	startTime := time.Now()
-	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(ctx, syncDB, rsAPI, []*gomatrixserverlib.HeaderedEvent{&requestedEvent}, nil, device.UserID, "context")
+	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(ctx, snapshot, rsAPI, []*gomatrixserverlib.HeaderedEvent{&requestedEvent}, nil, device.UserID, "context")
 	if err != nil {
 		logrus.WithError(err).Error("unable to apply history visibility filter")
 		return jsonerror.InternalServerError()
@@ -127,20 +133,20 @@ func Context(
 		}
 	}
 
-	eventsBefore, err := syncDB.SelectContextBeforeEvent(ctx, id, roomID, filter)
+	eventsBefore, err := snapshot.SelectContextBeforeEvent(ctx, id, roomID, filter)
 	if err != nil && err != sql.ErrNoRows {
 		logrus.WithError(err).Error("unable to fetch before events")
 		return jsonerror.InternalServerError()
 	}
 
-	_, eventsAfter, err := syncDB.SelectContextAfterEvent(ctx, id, roomID, filter)
+	_, eventsAfter, err := snapshot.SelectContextAfterEvent(ctx, id, roomID, filter)
 	if err != nil && err != sql.ErrNoRows {
 		logrus.WithError(err).Error("unable to fetch after events")
 		return jsonerror.InternalServerError()
 	}
 
 	startTime = time.Now()
-	eventsBeforeFiltered, eventsAfterFiltered, err := applyHistoryVisibilityOnContextEvents(ctx, syncDB, rsAPI, eventsBefore, eventsAfter, device.UserID)
+	eventsBeforeFiltered, eventsAfterFiltered, err := applyHistoryVisibilityOnContextEvents(ctx, snapshot, rsAPI, eventsBefore, eventsAfter, device.UserID)
 	if err != nil {
 		logrus.WithError(err).Error("unable to apply history visibility filter")
 		return jsonerror.InternalServerError()
@@ -152,7 +158,7 @@ func Context(
 	}).Debug("applied history visibility (context eventsBefore/eventsAfter)")
 
 	// TODO: Get the actual state at the last event returned by SelectContextAfterEvent
-	state, err := syncDB.CurrentState(ctx, roomID, &stateFilter, nil)
+	state, err := snapshot.CurrentState(ctx, roomID, &stateFilter, nil)
 	if err != nil {
 		logrus.WithError(err).Error("unable to fetch current room state")
 		return jsonerror.InternalServerError()
@@ -173,7 +179,7 @@ func Context(
 	if len(response.State) > filter.Limit {
 		response.State = response.State[len(response.State)-filter.Limit:]
 	}
-	start, end, err := getStartEnd(ctx, syncDB, eventsBefore, eventsAfter)
+	start, end, err := getStartEnd(ctx, snapshot, eventsBefore, eventsAfter)
 	if err == nil {
 		response.End = end.String()
 		response.Start = start.String()
@@ -188,7 +194,7 @@ func Context(
 // by combining the events before and after the context event. Returns the filtered events,
 // and an error, if any.
 func applyHistoryVisibilityOnContextEvents(
-	ctx context.Context, syncDB storage.Database, rsAPI roomserver.SyncRoomserverAPI,
+	ctx context.Context, snapshot storage.DatabaseTransaction, rsAPI roomserver.SyncRoomserverAPI,
 	eventsBefore, eventsAfter []*gomatrixserverlib.HeaderedEvent,
 	userID string,
 ) (filteredBefore, filteredAfter []*gomatrixserverlib.HeaderedEvent, err error) {
@@ -205,7 +211,7 @@ func applyHistoryVisibilityOnContextEvents(
 	}
 
 	allEvents := append(eventsBefore, eventsAfter...)
-	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(ctx, syncDB, rsAPI, allEvents, nil, userID, "context")
+	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(ctx, snapshot, rsAPI, allEvents, nil, userID, "context")
 	if err != nil {
 		return nil, nil, err
 	}
@@ -222,15 +228,15 @@ func applyHistoryVisibilityOnContextEvents(
 	return filteredBefore, filteredAfter, nil
 }
 
-func getStartEnd(ctx context.Context, syncDB storage.Database, startEvents, endEvents []*gomatrixserverlib.HeaderedEvent) (start, end types.TopologyToken, err error) {
+func getStartEnd(ctx context.Context, snapshot storage.DatabaseTransaction, startEvents, endEvents []*gomatrixserverlib.HeaderedEvent) (start, end types.TopologyToken, err error) {
 	if len(startEvents) > 0 {
-		start, err = syncDB.EventPositionInTopology(ctx, startEvents[0].EventID())
+		start, err = snapshot.EventPositionInTopology(ctx, startEvents[0].EventID())
 		if err != nil {
 			return
 		}
 	}
 	if len(endEvents) > 0 {
-		end, err = syncDB.EventPositionInTopology(ctx, endEvents[0].EventID())
+		end, err = snapshot.EventPositionInTopology(ctx, endEvents[0].EventID())
 	}
 	return
 }

syncapi/routing/messages.go

@@ -27,6 +27,7 @@ import (
 
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	"github.com/matrix-org/dendrite/internal/caching"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/syncapi/internal"
@@ -39,6 +40,7 @@ import (
 type messagesReq struct {
 	ctx              context.Context
 	db               storage.Database
+	snapshot         storage.DatabaseTransaction
 	rsAPI            api.SyncRoomserverAPI
 	cfg              *config.SyncAPI
 	roomID           string
@@ -70,6 +72,16 @@ func OnIncomingMessagesRequest(
 ) util.JSONResponse {
 	var err error
 
+	// NewDatabaseTransaction is used here instead of NewDatabaseSnapshot as we
+	// expect to be able to write to the database in response to a /messages
+	// request that requires backfilling from the roomserver or federation.
+	snapshot, err := db.NewDatabaseTransaction(req.Context())
+	if err != nil {
+		return jsonerror.InternalServerError()
+	}
+	var succeeded bool
+	defer sqlutil.EndTransactionWithCheck(snapshot, &succeeded, &err)
+
 	// check if the user has already forgotten about this room
 	isForgotten, roomExists, err := checkIsRoomForgotten(req.Context(), roomID, device.UserID, rsAPI)
 	if err != nil {
@@ -132,7 +144,7 @@ func OnIncomingMessagesRequest(
 			}
 		} else {
 			fromStream = &streamToken
-			from, err = db.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, backwardOrdering)
+			from, err = snapshot.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, backwardOrdering)
 			if err != nil {
 				logrus.WithError(err).Errorf("Failed to get topological position for streaming token %v", streamToken)
 				return jsonerror.InternalServerError()
@@ -154,7 +166,7 @@ func OnIncomingMessagesRequest(
 					JSON: jsonerror.InvalidArgumentValue("Invalid to parameter: " + err.Error()),
 				}
 			} else {
-				to, err = db.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, !backwardOrdering)
+				to, err = snapshot.StreamToTopologicalPosition(req.Context(), roomID, streamToken.PDUPosition, !backwardOrdering)
 				if err != nil {
 					logrus.WithError(err).Errorf("Failed to get topological position for streaming token %v", streamToken)
 					return jsonerror.InternalServerError()
@@ -165,7 +177,7 @@ func OnIncomingMessagesRequest(
 		// If "to" isn't provided, it defaults to either the earliest stream
 		// position (if we're going backward) or to the latest one (if we're
 		// going forward).
-		to, err = setToDefault(req.Context(), db, backwardOrdering, roomID)
+		to, err = setToDefault(req.Context(), snapshot, backwardOrdering, roomID)
 		if err != nil {
 			util.GetLogger(req.Context()).WithError(err).Error("setToDefault failed")
 			return jsonerror.InternalServerError()
@@ -186,6 +198,7 @@ func OnIncomingMessagesRequest(
 	mReq := messagesReq{
 		ctx:              req.Context(),
 		db:               db,
+		snapshot:         snapshot,
 		rsAPI:            rsAPI,
 		cfg:              cfg,
 		roomID:           roomID,
@@ -217,7 +230,7 @@ func OnIncomingMessagesRequest(
 		Start: start.String(),
 		End:   end.String(),
 	}
-	res.applyLazyLoadMembers(req.Context(), db, roomID, device, filter.LazyLoadMembers, lazyLoadCache)
+	res.applyLazyLoadMembers(req.Context(), snapshot, roomID, device, filter.LazyLoadMembers, lazyLoadCache)
 
 	// If we didn't return any events, set the end to an empty string, so it will be omitted
 	// in the response JSON.
@@ -229,6 +242,7 @@ func OnIncomingMessagesRequest(
 	}
 
 	// Respond with the events.
+	succeeded = true
 	return util.JSONResponse{
 		Code: http.StatusOK,
 		JSON: res,
@@ -239,7 +253,7 @@ func OnIncomingMessagesRequest(
 // LazyLoadMembers enabled.
 func (m *messagesResp) applyLazyLoadMembers(
 	ctx context.Context,
-	db storage.Database,
+	db storage.DatabaseTransaction,
 	roomID string,
 	device *userapi.Device,
 	lazyLoad bool,
@@ -292,7 +306,7 @@ func (r *messagesReq) retrieveEvents() (
 	end types.TopologyToken, err error,
 ) {
 	// Retrieve the events from the local database.
-	streamEvents, err := r.db.GetEventsInTopologicalRange(r.ctx, r.from, r.to, r.roomID, r.filter, r.backwardOrdering)
+	streamEvents, err := r.snapshot.GetEventsInTopologicalRange(r.ctx, r.from, r.to, r.roomID, r.filter, r.backwardOrdering)
 	if err != nil {
 		err = fmt.Errorf("GetEventsInRange: %w", err)
 		return
@@ -348,7 +362,7 @@ func (r *messagesReq) retrieveEvents() (
 
 	// Apply room history visibility filter
 	startTime := time.Now()
-	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(r.ctx, r.db, r.rsAPI, events, nil, r.device.UserID, "messages")
+	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(r.ctx, r.snapshot, r.rsAPI, events, nil, r.device.UserID, "messages")
 	logrus.WithFields(logrus.Fields{
 		"duration":      time.Since(startTime),
 		"room_id":       r.roomID,
@@ -366,7 +380,7 @@ func (r *messagesReq) getStartEnd(events []*gomatrixserverlib.HeaderedEvent) (st
 			// else to go. This seems to fix Element iOS from looping on /messages endlessly.
 			end = types.TopologyToken{}
 		} else {
-			end, err = r.db.EventPositionInTopology(
+			end, err = r.snapshot.EventPositionInTopology(
 				r.ctx, events[0].EventID(),
 			)
 			// A stream/topological position is a cursor located between two events.
@@ -378,7 +392,7 @@ func (r *messagesReq) getStartEnd(events []*gomatrixserverlib.HeaderedEvent) (st
 		}
 	} else {
 		start = *r.from
-		end, err = r.db.EventPositionInTopology(
+		end, err = r.snapshot.EventPositionInTopology(
 			r.ctx, events[len(events)-1].EventID(),
 		)
 	}
@@ -399,7 +413,7 @@ func (r *messagesReq) getStartEnd(events []*gomatrixserverlib.HeaderedEvent) (st
 func (r *messagesReq) handleEmptyEventsSlice() (
 	events []*gomatrixserverlib.HeaderedEvent, err error,
 ) {
-	backwardExtremities, err := r.db.BackwardExtremitiesForRoom(r.ctx, r.roomID)
+	backwardExtremities, err := r.snapshot.BackwardExtremitiesForRoom(r.ctx, r.roomID)
 
 	// Check if we have backward extremities for this room.
 	if len(backwardExtremities) > 0 {
@@ -443,7 +457,7 @@ func (r *messagesReq) handleNonEmptyEventsSlice(streamEvents []types.StreamEvent
 	}
 
 	// Check if the slice contains a backward extremity.
-	backwardExtremities, err := r.db.BackwardExtremitiesForRoom(r.ctx, r.roomID)
+	backwardExtremities, err := r.snapshot.BackwardExtremitiesForRoom(r.ctx, r.roomID)
 	if err != nil {
 		return
 	}
@@ -463,7 +477,7 @@ func (r *messagesReq) handleNonEmptyEventsSlice(streamEvents []types.StreamEvent
 	}
 
 	// Append the events ve previously retrieved locally.
-	events = append(events, r.db.StreamEventsToEvents(nil, streamEvents)...)
+	events = append(events, r.snapshot.StreamEventsToEvents(nil, streamEvents)...)
 	sort.Sort(eventsByDepth(events))
 
 	return
@@ -553,7 +567,7 @@ func (r *messagesReq) backfill(roomID string, backwardsExtremities map[string][]
 // Returns an error if there was an issue with retrieving the latest position
 // from the database
 func setToDefault(
-	ctx context.Context, db storage.Database, backwardOrdering bool,
+	ctx context.Context, snapshot storage.DatabaseTransaction, backwardOrdering bool,
 	roomID string,
 ) (to types.TopologyToken, err error) {
 	if backwardOrdering {
@@ -561,7 +575,7 @@ func setToDefault(
 		// this is because Database.GetEventsInTopologicalRange is exclusive of the lower-bound.
 		to = types.TopologyToken{}
 	} else {
-		to, err = db.MaxTopologicalPosition(ctx, roomID)
+		to, err = snapshot.MaxTopologicalPosition(ctx, roomID)
 	}
 
 	return

syncapi/routing/search.go

@@ -61,8 +61,14 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 		searchReq.SearchCategories.RoomEvents.Filter.Limit = 5
 	}
 
+	snapshot, err := syncDB.NewDatabaseSnapshot(req.Context())
+	if err != nil {
+		return jsonerror.InternalServerError()
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+
 	// only search rooms the user is actually joined to
-	joinedRooms, err := syncDB.RoomIDsWithMembership(ctx, device.UserID, "join")
+	joinedRooms, err := snapshot.RoomIDsWithMembership(ctx, device.UserID, "join")
 	if err != nil {
 		return jsonerror.InternalServerError()
 	}
@@ -161,12 +167,12 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 
 	stateForRooms := make(map[string][]gomatrixserverlib.ClientEvent)
 	for _, event := range evs {
-		eventsBefore, eventsAfter, err := contextEvents(ctx, syncDB, event, roomFilter, searchReq)
+		eventsBefore, eventsAfter, err := contextEvents(ctx, snapshot, event, roomFilter, searchReq)
 		if err != nil {
 			logrus.WithError(err).Error("failed to get context events")
 			return jsonerror.InternalServerError()
 		}
-		startToken, endToken, err := getStartEnd(ctx, syncDB, eventsBefore, eventsAfter)
+		startToken, endToken, err := getStartEnd(ctx, snapshot, eventsBefore, eventsAfter)
 		if err != nil {
 			logrus.WithError(err).Error("failed to get start/end")
 			return jsonerror.InternalServerError()
@@ -176,7 +182,7 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 		for _, ev := range append(eventsBefore, eventsAfter...) {
 			profile, ok := knownUsersProfiles[event.Sender()]
 			if !ok {
-				stateEvent, err := syncDB.GetStateEvent(ctx, ev.RoomID(), gomatrixserverlib.MRoomMember, ev.Sender())
+				stateEvent, err := snapshot.GetStateEvent(ctx, ev.RoomID(), gomatrixserverlib.MRoomMember, ev.Sender())
 				if err != nil {
 					logrus.WithError(err).WithField("user_id", event.Sender()).Warn("failed to query userprofile")
 					continue
@@ -209,7 +215,7 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 		groups[event.RoomID()] = roomGroup
 		if _, ok := stateForRooms[event.RoomID()]; searchReq.SearchCategories.RoomEvents.IncludeState && !ok {
 			stateFilter := gomatrixserverlib.DefaultStateFilter()
-			state, err := syncDB.CurrentState(ctx, event.RoomID(), &stateFilter, nil)
+			state, err := snapshot.CurrentState(ctx, event.RoomID(), &stateFilter, nil)
 			if err != nil {
 				logrus.WithError(err).Error("unable to get current state")
 				return jsonerror.InternalServerError()
@@ -252,24 +258,24 @@ func Search(req *http.Request, device *api.Device, syncDB storage.Database, fts
 // contextEvents returns the events around a given eventID
 func contextEvents(
 	ctx context.Context,
-	syncDB storage.Database,
+	snapshot storage.DatabaseTransaction,
 	event *gomatrixserverlib.HeaderedEvent,
 	roomFilter *gomatrixserverlib.RoomEventFilter,
 	searchReq SearchRequest,
 ) ([]*gomatrixserverlib.HeaderedEvent, []*gomatrixserverlib.HeaderedEvent, error) {
-	id, _, err := syncDB.SelectContextEvent(ctx, event.RoomID(), event.EventID())
+	id, _, err := snapshot.SelectContextEvent(ctx, event.RoomID(), event.EventID())
 	if err != nil {
 		logrus.WithError(err).Error("failed to query context event")
 		return nil, nil, err
 	}
 	roomFilter.Limit = searchReq.SearchCategories.RoomEvents.EventContext.BeforeLimit
-	eventsBefore, err := syncDB.SelectContextBeforeEvent(ctx, id, event.RoomID(), roomFilter)
+	eventsBefore, err := snapshot.SelectContextBeforeEvent(ctx, id, event.RoomID(), roomFilter)
 	if err != nil {
 		logrus.WithError(err).Error("failed to query before context event")
 		return nil, nil, err
 	}
 	roomFilter.Limit = searchReq.SearchCategories.RoomEvents.EventContext.AfterLimit
-	_, eventsAfter, err := syncDB.SelectContextAfterEvent(ctx, id, event.RoomID(), roomFilter)
+	_, eventsAfter, err := snapshot.SelectContextAfterEvent(ctx, id, event.RoomID(), roomFilter)
 	if err != nil {
 		logrus.WithError(err).Error("failed to query after context event")
 		return nil, nil, err

syncapi/storage/interface.go

@@ -17,19 +17,17 @@ package storage
 import (
 	"context"
 
-	"github.com/matrix-org/dendrite/internal/eventutil"
-
 	"github.com/matrix-org/gomatrixserverlib"
 
+	"github.com/matrix-org/dendrite/internal/eventutil"
 	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/syncapi/storage/shared"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 )
 
-type Database interface {
+type DatabaseTransaction interface {
-	Presence
 	SharedUsers
-	Notifications
 
 	MaxStreamPositionForPDUs(ctx context.Context) (types.StreamPosition, error)
 	MaxStreamPositionForReceipts(ctx context.Context) (types.StreamPosition, error)
@@ -37,6 +35,7 @@ type Database interface {
 	MaxStreamPositionForAccountData(ctx context.Context) (types.StreamPosition, error)
 	MaxStreamPositionForSendToDeviceMessages(ctx context.Context) (types.StreamPosition, error)
 	MaxStreamPositionForNotificationData(ctx context.Context) (types.StreamPosition, error)
+	MaxStreamPositionForPresence(ctx context.Context) (types.StreamPosition, error)
 
 	CurrentState(ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.StateFilter, excludeEventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error)
 	GetStateDeltasForFullStateSync(ctx context.Context, device *userapi.Device, r types.Range, userID string, stateFilter *gomatrixserverlib.StateFilter) ([]types.StateDelta, []string, error)
@@ -44,23 +43,77 @@ type Database interface {
 	RoomIDsWithMembership(ctx context.Context, userID string, membership string) ([]string, error)
 	MembershipCount(ctx context.Context, roomID, membership string, pos types.StreamPosition) (int, error)
 	GetRoomHeroes(ctx context.Context, roomID, userID string, memberships []string) ([]string, error)
-
 	RecentEvents(ctx context.Context, roomID string, r types.Range, eventFilter *gomatrixserverlib.RoomEventFilter, chronologicalOrder bool, onlySyncEvents bool) ([]types.StreamEvent, bool, error)
-
 	GetBackwardTopologyPos(ctx context.Context, events []types.StreamEvent) (types.TopologyToken, error)
 	PositionInTopology(ctx context.Context, eventID string) (pos types.StreamPosition, spos types.StreamPosition, err error)
-
+	InviteEventsInRange(ctx context.Context, targetUserID string, r types.Range) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, types.StreamPosition, error)
-	InviteEventsInRange(ctx context.Context, targetUserID string, r types.Range) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, error)
 	PeeksInRange(ctx context.Context, userID, deviceID string, r types.Range) (peeks []types.Peek, err error)
 	RoomReceiptsAfter(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) (types.StreamPosition, []types.OutputReceiptEvent, error)
-
 	// AllJoinedUsersInRooms returns a map of room ID to a list of all joined user IDs.
 	AllJoinedUsersInRooms(ctx context.Context) (map[string][]string, error)
 	// AllJoinedUsersInRoom returns a map of room ID to a list of all joined user IDs for a given room.
 	AllJoinedUsersInRoom(ctx context.Context, roomIDs []string) (map[string][]string, error)
-
 	// AllPeekingDevicesInRooms returns a map of room ID to a list of all peeking devices.
 	AllPeekingDevicesInRooms(ctx context.Context) (map[string][]types.PeekingDevice, error)
+	// Events lookups a list of event by their event ID.
+	// Returns a list of events matching the requested IDs found in the database.
+	// If an event is not found in the database then it will be omitted from the list.
+	// Returns an error if there was a problem talking with the database.
+	// Does not include any transaction IDs in the returned events.
+	Events(ctx context.Context, eventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error)
+	// GetStateEvent returns the Matrix state event of a given type for a given room with a given state key
+	// If no event could be found, returns nil
+	// If there was an issue during the retrieval, returns an error
+	GetStateEvent(ctx context.Context, roomID, evType, stateKey string) (*gomatrixserverlib.HeaderedEvent, error)
+	// GetStateEventsForRoom fetches the state events for a given room.
+	// Returns an empty slice if no state events could be found for this room.
+	// Returns an error if there was an issue with the retrieval.
+	GetStateEventsForRoom(ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.StateFilter) (stateEvents []*gomatrixserverlib.HeaderedEvent, err error)
+	// GetAccountDataInRange returns all account data for a given user inserted or
+	// updated between two given positions
+	// Returns a map following the format data[roomID] = []dataTypes
+	// If no data is retrieved, returns an empty map
+	// If there was an issue with the retrieval, returns an error
+	GetAccountDataInRange(ctx context.Context, userID string, r types.Range, accountDataFilterPart *gomatrixserverlib.EventFilter) (map[string][]string, types.StreamPosition, error)
+	// GetEventsInTopologicalRange retrieves all of the events on a given ordering using the given extremities and limit. If backwardsOrdering is true, the most recent event must be first, else last.
+	GetEventsInTopologicalRange(ctx context.Context, from, to *types.TopologyToken, roomID string, filter *gomatrixserverlib.RoomEventFilter, backwardOrdering bool) (events []types.StreamEvent, err error)
+	// EventPositionInTopology returns the depth and stream position of the given event.
+	EventPositionInTopology(ctx context.Context, eventID string) (types.TopologyToken, error)
+	// BackwardExtremitiesForRoom returns a map of backwards extremity event ID to a list of its prev_events.
+	BackwardExtremitiesForRoom(ctx context.Context, roomID string) (backwardExtremities map[string][]string, err error)
+	// MaxTopologicalPosition returns the highest topological position for a given room.
+	MaxTopologicalPosition(ctx context.Context, roomID string) (types.TopologyToken, error)
+	// StreamEventsToEvents converts streamEvent to Event. If device is non-nil and
+	// matches the streamevent.transactionID device then the transaction ID gets
+	// added to the unsigned section of the output event.
+	StreamEventsToEvents(device *userapi.Device, in []types.StreamEvent) []*gomatrixserverlib.HeaderedEvent
+	// SendToDeviceUpdatesForSync returns a list of send-to-device updates. It returns the
+	// relevant events within the given ranges for the supplied user ID and device ID.
+	SendToDeviceUpdatesForSync(ctx context.Context, userID, deviceID string, from, to types.StreamPosition) (pos types.StreamPosition, events []types.SendToDeviceEvent, err error)
+	// GetRoomReceipts gets all receipts for a given roomID
+	GetRoomReceipts(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]types.OutputReceiptEvent, error)
+	SelectContextEvent(ctx context.Context, roomID, eventID string) (int, gomatrixserverlib.HeaderedEvent, error)
+	SelectContextBeforeEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) ([]*gomatrixserverlib.HeaderedEvent, error)
+	SelectContextAfterEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) (int, []*gomatrixserverlib.HeaderedEvent, error)
+	StreamToTopologicalPosition(ctx context.Context, roomID string, streamPos types.StreamPosition, backwardOrdering bool) (types.TopologyToken, error)
+	IgnoresForUser(ctx context.Context, userID string) (*types.IgnoredUsers, error)
+	// SelectMembershipForUser returns the membership of the user before and including the given position. If no membership can be found
+	// returns "leave", the topological position and no error. If an error occurs, other than sql.ErrNoRows, returns that and an empty
+	// string as the membership.
+	SelectMembershipForUser(ctx context.Context, roomID, userID string, pos int64) (membership string, topologicalPos int, err error)
+	// getUserUnreadNotificationCountsForRooms returns the unread notifications for the given rooms
+	GetUserUnreadNotificationCountsForRooms(ctx context.Context, userID string, roomIDs map[string]string) (map[string]*eventutil.NotificationData, error)
+	GetPresence(ctx context.Context, userID string) (*types.PresenceInternal, error)
+	PresenceAfter(ctx context.Context, after types.StreamPosition, filter gomatrixserverlib.EventFilter) (map[string]*types.PresenceInternal, error)
+}
+
+type Database interface {
+	Presence
+	Notifications
+
+	NewDatabaseSnapshot(ctx context.Context) (*shared.DatabaseTransaction, error)
+	NewDatabaseTransaction(ctx context.Context) (*shared.DatabaseTransaction, error)
+
 	// Events lookups a list of event by their event ID.
 	// Returns a list of events matching the requested IDs found in the database.
 	// If an event is not found in the database then it will be omitted from the list.
@@ -77,20 +130,6 @@ type Database interface {
 	// PurgeRoomState completely purges room state from the sync API. This is done when
 	// receiving an output event that completely resets the state.
 	PurgeRoomState(ctx context.Context, roomID string) error
-	// GetStateEvent returns the Matrix state event of a given type for a given room with a given state key
-	// If no event could be found, returns nil
-	// If there was an issue during the retrieval, returns an error
-	GetStateEvent(ctx context.Context, roomID, evType, stateKey string) (*gomatrixserverlib.HeaderedEvent, error)
-	// GetStateEventsForRoom fetches the state events for a given room.
-	// Returns an empty slice if no state events could be found for this room.
-	// Returns an error if there was an issue with the retrieval.
-	GetStateEventsForRoom(ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.StateFilter) (stateEvents []*gomatrixserverlib.HeaderedEvent, err error)
-	// GetAccountDataInRange returns all account data for a given user inserted or
-	// updated between two given positions
-	// Returns a map following the format data[roomID] = []dataTypes
-	// If no data is retrieved, returns an empty map
-	// If there was an issue with the retrieval, returns an error
-	GetAccountDataInRange(ctx context.Context, userID string, r types.Range, accountDataFilterPart *gomatrixserverlib.EventFilter) (map[string][]string, types.StreamPosition, error)
 	// UpsertAccountData keeps track of new or updated account data, by saving the type
 	// of the new/updated data, and the user ID and room ID the data is related to (empty)
 	// room ID means the data isn't specific to any room)
@@ -114,21 +153,6 @@ type Database interface {
 	// DeletePeek deletes all peeks for a given room by a given user
 	// Returns an error if there was a problem communicating with the database.
 	DeletePeeks(ctx context.Context, RoomID, UserID string) (types.StreamPosition, error)
-	// GetEventsInTopologicalRange retrieves all of the events on a given ordering using the given extremities and limit. If backwardsOrdering is true, the most recent event must be first, else last.
-	GetEventsInTopologicalRange(ctx context.Context, from, to *types.TopologyToken, roomID string, filter *gomatrixserverlib.RoomEventFilter, backwardOrdering bool) (events []types.StreamEvent, err error)
-	// EventPositionInTopology returns the depth and stream position of the given event.
-	EventPositionInTopology(ctx context.Context, eventID string) (types.TopologyToken, error)
-	// BackwardExtremitiesForRoom returns a map of backwards extremity event ID to a list of its prev_events.
-	BackwardExtremitiesForRoom(ctx context.Context, roomID string) (backwardExtremities map[string][]string, err error)
-	// MaxTopologicalPosition returns the highest topological position for a given room.
-	MaxTopologicalPosition(ctx context.Context, roomID string) (types.TopologyToken, error)
-	// StreamEventsToEvents converts streamEvent to Event. If device is non-nil and
-	// matches the streamevent.transactionID device then the transaction ID gets
-	// added to the unsigned section of the output event.
-	StreamEventsToEvents(device *userapi.Device, in []types.StreamEvent) []*gomatrixserverlib.HeaderedEvent
-	// SendToDeviceUpdatesForSync returns a list of send-to-device updates. It returns the
-	// relevant events within the given ranges for the supplied user ID and device ID.
-	SendToDeviceUpdatesForSync(ctx context.Context, userID, deviceID string, from, to types.StreamPosition) (pos types.StreamPosition, events []types.SendToDeviceEvent, err error)
 	// StoreNewSendForDeviceMessage stores a new send-to-device event for a user's device.
 	StoreNewSendForDeviceMessage(ctx context.Context, userID, deviceID string, event gomatrixserverlib.SendToDeviceEvent) (types.StreamPosition, error)
 	// CleanSendToDeviceUpdates removes all send-to-device messages BEFORE the specified
@@ -146,29 +170,13 @@ type Database interface {
 	RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *gomatrixserverlib.HeaderedEvent) error
 	// StoreReceipt stores new receipt events
 	StoreReceipt(ctx context.Context, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error)
-	// GetRoomReceipts gets all receipts for a given roomID
-	GetRoomReceipts(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]types.OutputReceiptEvent, error)
-
-	SelectContextEvent(ctx context.Context, roomID, eventID string) (int, gomatrixserverlib.HeaderedEvent, error)
-	SelectContextBeforeEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) ([]*gomatrixserverlib.HeaderedEvent, error)
-	SelectContextAfterEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) (int, []*gomatrixserverlib.HeaderedEvent, error)
-
-	StreamToTopologicalPosition(ctx context.Context, roomID string, streamPos types.StreamPosition, backwardOrdering bool) (types.TopologyToken, error)
-
-	IgnoresForUser(ctx context.Context, userID string) (*types.IgnoredUsers, error)
 	UpdateIgnoresForUser(ctx context.Context, userID string, ignores *types.IgnoredUsers) error
-	// SelectMembershipForUser returns the membership of the user before and including the given position. If no membership can be found
-	// returns "leave", the topological position and no error. If an error occurs, other than sql.ErrNoRows, returns that and an empty
-	// string as the membership.
-	SelectMembershipForUser(ctx context.Context, roomID, userID string, pos int64) (membership string, topologicalPos int, err error)
 	ReIndex(ctx context.Context, limit, afterID int64) (map[int64]gomatrixserverlib.HeaderedEvent, error)
 }
 
 type Presence interface {
-	UpdatePresence(ctx context.Context, userID string, presence types.Presence, statusMsg *string, lastActiveTS gomatrixserverlib.Timestamp, fromSync bool) (types.StreamPosition, error)
 	GetPresence(ctx context.Context, userID string) (*types.PresenceInternal, error)
-	PresenceAfter(ctx context.Context, after types.StreamPosition, filter gomatrixserverlib.EventFilter) (map[string]*types.PresenceInternal, error)
+	UpdatePresence(ctx context.Context, userID string, presence types.Presence, statusMsg *string, lastActiveTS gomatrixserverlib.Timestamp, fromSync bool) (types.StreamPosition, error)
-	MaxStreamPositionForPresence(ctx context.Context) (types.StreamPosition, error)
 }
 
 type SharedUsers interface {
@@ -179,7 +187,4 @@ type SharedUsers interface {
 type Notifications interface {
 	// UpsertRoomUnreadNotificationCounts updates the notification statistics about a (user, room) key.
 	UpsertRoomUnreadNotificationCounts(ctx context.Context, userID, roomID string, notificationCount, highlightCount int) (types.StreamPosition, error)
-
-	// getUserUnreadNotificationCountsForRooms returns the unread notifications for the given rooms
-	GetUserUnreadNotificationCountsForRooms(ctx context.Context, userID string, roomIDs map[string]string) (map[string]*eventutil.NotificationData, error)
 }

syncapi/storage/postgres/invites_table.go

@@ -55,7 +55,7 @@ const deleteInviteEventSQL = "" +
 	"UPDATE syncapi_invite_events SET deleted=TRUE, id=nextval('syncapi_stream_id') WHERE event_id = $1 AND deleted=FALSE RETURNING id"
 
 const selectInviteEventsInRangeSQL = "" +
-	"SELECT room_id, headered_event_json, deleted FROM syncapi_invite_events" +
+	"SELECT id, room_id, headered_event_json, deleted FROM syncapi_invite_events" +
 	" WHERE target_user_id = $1 AND id > $2 AND id <= $3" +
 	" ORDER BY id DESC"
 
@@ -121,23 +121,28 @@ func (s *inviteEventsStatements) DeleteInviteEvent(
 // active invites for the target user ID in the supplied range.
 func (s *inviteEventsStatements) SelectInviteEventsInRange(
 	ctx context.Context, txn *sql.Tx, targetUserID string, r types.Range,
-) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, error) {
+) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, types.StreamPosition, error) {
+	var lastPos types.StreamPosition
 	stmt := sqlutil.TxStmt(txn, s.selectInviteEventsInRangeStmt)
 	rows, err := stmt.QueryContext(ctx, targetUserID, r.Low(), r.High())
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, lastPos, err
 	}
 	defer internal.CloseAndLogIfError(ctx, rows, "selectInviteEventsInRange: rows.close() failed")
 	result := map[string]*gomatrixserverlib.HeaderedEvent{}
 	retired := map[string]*gomatrixserverlib.HeaderedEvent{}
 	for rows.Next() {
 		var (
+			id        types.StreamPosition
 			roomID    string
 			eventJSON []byte
 			deleted   bool
 		)
-		if err = rows.Scan(&roomID, &eventJSON, &deleted); err != nil {
+		if err = rows.Scan(&id, &roomID, &eventJSON, &deleted); err != nil {
-			return nil, nil, err
+			return nil, nil, lastPos, err
+		}
+		if id > lastPos {
+			lastPos = id
 		}
 
 		// if we have seen this room before, it has a higher stream position and hence takes priority
@@ -150,7 +155,7 @@ func (s *inviteEventsStatements) SelectInviteEventsInRange(
 
 		var event *gomatrixserverlib.HeaderedEvent
 		if err := json.Unmarshal(eventJSON, &event); err != nil {
-			return nil, nil, err
+			return nil, nil, lastPos, err
 		}
 
 		if deleted {
@@ -159,7 +164,10 @@ func (s *inviteEventsStatements) SelectInviteEventsInRange(
 			result[roomID] = event
 		}
 	}
-	return result, retired, rows.Err()
+	if lastPos == 0 {
+		lastPos = r.To
+	}
+	return result, retired, lastPos, rows.Err()
 }
 
 func (s *inviteEventsStatements) SelectMaxInviteID(

syncapi/storage/shared/storage_consumer.go

@@ -0,0 +1,586 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package shared
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+
+	"github.com/tidwall/gjson"
+
+	userapi "github.com/matrix-org/dendrite/userapi/api"
+
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+
+	"github.com/matrix-org/dendrite/internal/eventutil"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/syncapi/storage/tables"
+	"github.com/matrix-org/dendrite/syncapi/types"
+)
+
+// Database is a temporary struct until we have made syncserver.go the same for both pq/sqlite
+// For now this contains the shared functions
+type Database struct {
+	DB                  *sql.DB
+	Writer              sqlutil.Writer
+	Invites             tables.Invites
+	Peeks               tables.Peeks
+	AccountData         tables.AccountData
+	OutputEvents        tables.Events
+	Topology            tables.Topology
+	CurrentRoomState    tables.CurrentRoomState
+	BackwardExtremities tables.BackwardsExtremities
+	SendToDevice        tables.SendToDevice
+	Filter              tables.Filter
+	Receipts            tables.Receipts
+	Memberships         tables.Memberships
+	NotificationData    tables.NotificationData
+	Ignores             tables.Ignores
+	Presence            tables.Presence
+}
+
+func (d *Database) NewDatabaseSnapshot(ctx context.Context) (*DatabaseTransaction, error) {
+	return d.NewDatabaseTransaction(ctx)
+
+	/*
+		TODO: Repeatable read is probably the right thing to do here,
+		but it seems to cause some problems with the invite tests, so
+		need to investigate that further.
+
+		txn, err := d.DB.BeginTx(ctx, &sql.TxOptions{
+			// Set the isolation level so that we see a snapshot of the database.
+			// In PostgreSQL repeatable read transactions will see a snapshot taken
+			// at the first query, and since the transaction is read-only it can't
+			// run into any serialisation errors.
+			// https://www.postgresql.org/docs/9.5/static/transaction-iso.html#XACT-REPEATABLE-READ
+			Isolation: sql.LevelRepeatableRead,
+			ReadOnly:  true,
+		})
+		if err != nil {
+			return nil, err
+		}
+		return &DatabaseTransaction{
+			Database: d,
+			txn:      txn,
+		}, nil
+	*/
+}
+
+func (d *Database) NewDatabaseTransaction(ctx context.Context) (*DatabaseTransaction, error) {
+	txn, err := d.DB.BeginTx(ctx, nil)
+	if err != nil {
+		return nil, err
+	}
+	return &DatabaseTransaction{
+		Database: d,
+		txn:      txn,
+	}, nil
+}
+
+func (d *Database) Events(ctx context.Context, eventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error) {
+	streamEvents, err := d.OutputEvents.SelectEvents(ctx, nil, eventIDs, nil, false)
+	if err != nil {
+		return nil, err
+	}
+
+	// We don't include a device here as we only include transaction IDs in
+	// incremental syncs.
+	return d.StreamEventsToEvents(nil, streamEvents), nil
+}
+
+// AddInviteEvent stores a new invite event for a user.
+// If the invite was successfully stored this returns the stream ID it was stored at.
+// Returns an error if there was a problem communicating with the database.
+func (d *Database) AddInviteEvent(
+	ctx context.Context, inviteEvent *gomatrixserverlib.HeaderedEvent,
+) (sp types.StreamPosition, err error) {
+	_ = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.Invites.InsertInviteEvent(ctx, txn, inviteEvent)
+		return err
+	})
+	return
+}
+
+// RetireInviteEvent removes an old invite event from the database.
+// Returns an error if there was a problem communicating with the database.
+func (d *Database) RetireInviteEvent(
+	ctx context.Context, inviteEventID string,
+) (sp types.StreamPosition, err error) {
+	_ = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.Invites.DeleteInviteEvent(ctx, txn, inviteEventID)
+		return err
+	})
+	return
+}
+
+// AddPeek tracks the fact that a user has started peeking.
+// If the peek was successfully stored this returns the stream ID it was stored at.
+// Returns an error if there was a problem communicating with the database.
+func (d *Database) AddPeek(
+	ctx context.Context, roomID, userID, deviceID string,
+) (sp types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.Peeks.InsertPeek(ctx, txn, roomID, userID, deviceID)
+		return err
+	})
+	return
+}
+
+// DeletePeek tracks the fact that a user has stopped peeking from the specified
+// device. If the peeks was successfully deleted this returns the stream ID it was
+// stored at. Returns an error if there was a problem communicating with the database.
+func (d *Database) DeletePeek(
+	ctx context.Context, roomID, userID, deviceID string,
+) (sp types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.Peeks.DeletePeek(ctx, txn, roomID, userID, deviceID)
+		return err
+	})
+	if err == sql.ErrNoRows {
+		sp = 0
+		err = nil
+	}
+	return
+}
+
+// DeletePeeks tracks the fact that a user has stopped peeking from all devices
+// If the peeks was successfully deleted this returns the stream ID it was stored at.
+// Returns an error if there was a problem communicating with the database.
+func (d *Database) DeletePeeks(
+	ctx context.Context, roomID, userID string,
+) (sp types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.Peeks.DeletePeeks(ctx, txn, roomID, userID)
+		return err
+	})
+	if err == sql.ErrNoRows {
+		sp = 0
+		err = nil
+	}
+	return
+}
+
+// UpsertAccountData keeps track of new or updated account data, by saving the type
+// of the new/updated data, and the user ID and room ID the data is related to (empty)
+// room ID means the data isn't specific to any room)
+// If no data with the given type, user ID and room ID exists in the database,
+// creates a new row, else update the existing one
+// Returns an error if there was an issue with the upsert
+func (d *Database) UpsertAccountData(
+	ctx context.Context, userID, roomID, dataType string,
+) (sp types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		sp, err = d.AccountData.InsertAccountData(ctx, txn, userID, roomID, dataType)
+		return err
+	})
+	return
+}
+
+func (d *Database) StreamEventsToEvents(device *userapi.Device, in []types.StreamEvent) []*gomatrixserverlib.HeaderedEvent {
+	out := make([]*gomatrixserverlib.HeaderedEvent, len(in))
+	for i := 0; i < len(in); i++ {
+		out[i] = in[i].HeaderedEvent
+		if device != nil && in[i].TransactionID != nil {
+			if device.UserID == in[i].Sender() && device.SessionID == in[i].TransactionID.SessionID {
+				err := out[i].SetUnsignedField(
+					"transaction_id", in[i].TransactionID.TransactionID,
+				)
+				if err != nil {
+					logrus.WithFields(logrus.Fields{
+						"event_id": out[i].EventID(),
+					}).WithError(err).Warnf("Failed to add transaction ID to event")
+				}
+			}
+		}
+	}
+	return out
+}
+
+// handleBackwardExtremities adds this event as a backwards extremity if and only if we do not have all of
+// the events listed in the event's 'prev_events'. This function also updates the backwards extremities table
+// to account for the fact that the given event is no longer a backwards extremity, but may be marked as such.
+// This function should always be called within a sqlutil.Writer for safety in SQLite.
+func (d *Database) handleBackwardExtremities(ctx context.Context, txn *sql.Tx, ev *gomatrixserverlib.HeaderedEvent) error {
+	if err := d.BackwardExtremities.DeleteBackwardExtremity(ctx, txn, ev.RoomID(), ev.EventID()); err != nil {
+		return err
+	}
+
+	// Check if we have all of the event's previous events. If an event is
+	// missing, add it to the room's backward extremities.
+	prevEvents, err := d.OutputEvents.SelectEvents(ctx, txn, ev.PrevEventIDs(), nil, false)
+	if err != nil {
+		return err
+	}
+	var found bool
+	for _, eID := range ev.PrevEventIDs() {
+		found = false
+		for _, prevEv := range prevEvents {
+			if eID == prevEv.EventID() {
+				found = true
+			}
+		}
+
+		// If the event is missing, consider it a backward extremity.
+		if !found {
+			if err = d.BackwardExtremities.InsertsBackwardExtremity(ctx, txn, ev.RoomID(), ev.EventID(), eID); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func (d *Database) PurgeRoomState(
+	ctx context.Context, roomID string,
+) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		// If the event is a create event then we'll delete all of the existing
+		// data for the room. The only reason that a create event would be replayed
+		// to us in this way is if we're about to receive the entire room state.
+		if err := d.CurrentRoomState.DeleteRoomStateForRoom(ctx, txn, roomID); err != nil {
+			return fmt.Errorf("d.CurrentRoomState.DeleteRoomStateForRoom: %w", err)
+		}
+		return nil
+	})
+}
+
+func (d *Database) WriteEvent(
+	ctx context.Context,
+	ev *gomatrixserverlib.HeaderedEvent,
+	addStateEvents []*gomatrixserverlib.HeaderedEvent,
+	addStateEventIDs, removeStateEventIDs []string,
+	transactionID *api.TransactionID, excludeFromSync bool,
+	historyVisibility gomatrixserverlib.HistoryVisibility,
+) (pduPosition types.StreamPosition, returnErr error) {
+	returnErr = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		var err error
+		ev.Visibility = historyVisibility
+		pos, err := d.OutputEvents.InsertEvent(
+			ctx, txn, ev, addStateEventIDs, removeStateEventIDs, transactionID, excludeFromSync, historyVisibility,
+		)
+		if err != nil {
+			return fmt.Errorf("d.OutputEvents.InsertEvent: %w", err)
+		}
+		pduPosition = pos
+		var topoPosition types.StreamPosition
+		if topoPosition, err = d.Topology.InsertEventInTopology(ctx, txn, ev, pos); err != nil {
+			return fmt.Errorf("d.Topology.InsertEventInTopology: %w", err)
+		}
+
+		if err = d.handleBackwardExtremities(ctx, txn, ev); err != nil {
+			return fmt.Errorf("d.handleBackwardExtremities: %w", err)
+		}
+
+		if len(addStateEvents) == 0 && len(removeStateEventIDs) == 0 {
+			// Nothing to do, the event may have just been a message event.
+			return nil
+		}
+		for i := range addStateEvents {
+			addStateEvents[i].Visibility = historyVisibility
+		}
+		return d.updateRoomState(ctx, txn, removeStateEventIDs, addStateEvents, pduPosition, topoPosition)
+	})
+
+	return pduPosition, returnErr
+}
+
+// This function should always be called within a sqlutil.Writer for safety in SQLite.
+func (d *Database) updateRoomState(
+	ctx context.Context, txn *sql.Tx,
+	removedEventIDs []string,
+	addedEvents []*gomatrixserverlib.HeaderedEvent,
+	pduPosition types.StreamPosition,
+	topoPosition types.StreamPosition,
+) error {
+	// remove first, then add, as we do not ever delete state, but do replace state which is a remove followed by an add.
+	for _, eventID := range removedEventIDs {
+		if err := d.CurrentRoomState.DeleteRoomStateByEventID(ctx, txn, eventID); err != nil {
+			return fmt.Errorf("d.CurrentRoomState.DeleteRoomStateByEventID: %w", err)
+		}
+	}
+
+	for _, event := range addedEvents {
+		if event.StateKey() == nil {
+			// ignore non state events
+			continue
+		}
+		var membership *string
+		if event.Type() == "m.room.member" {
+			value, err := event.Membership()
+			if err != nil {
+				return fmt.Errorf("event.Membership: %w", err)
+			}
+			membership = &value
+			if err = d.Memberships.UpsertMembership(ctx, txn, event, pduPosition, topoPosition); err != nil {
+				return fmt.Errorf("d.Memberships.UpsertMembership: %w", err)
+			}
+		}
+
+		if err := d.CurrentRoomState.UpsertRoomState(ctx, txn, event, membership, pduPosition); err != nil {
+			return fmt.Errorf("d.CurrentRoomState.UpsertRoomState: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func (d *Database) GetFilter(
+	ctx context.Context, target *gomatrixserverlib.Filter, localpart string, filterID string,
+) error {
+	return d.Filter.SelectFilter(ctx, nil, target, localpart, filterID)
+}
+
+func (d *Database) PutFilter(
+	ctx context.Context, localpart string, filter *gomatrixserverlib.Filter,
+) (string, error) {
+	var filterID string
+	var err error
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		filterID, err = d.Filter.InsertFilter(ctx, txn, filter, localpart)
+		return err
+	})
+	return filterID, err
+}
+
+func (d *Database) RedactEvent(ctx context.Context, redactedEventID string, redactedBecause *gomatrixserverlib.HeaderedEvent) error {
+	redactedEvents, err := d.Events(ctx, []string{redactedEventID})
+	if err != nil {
+		return err
+	}
+	if len(redactedEvents) == 0 {
+		logrus.WithField("event_id", redactedEventID).WithField("redaction_event", redactedBecause.EventID()).Warnf("missing redacted event for redaction")
+		return nil
+	}
+	eventToRedact := redactedEvents[0].Unwrap()
+	redactionEvent := redactedBecause.Unwrap()
+	if err = eventutil.RedactEvent(redactionEvent, eventToRedact); err != nil {
+		return err
+	}
+
+	newEvent := eventToRedact.Headered(redactedBecause.RoomVersion)
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.OutputEvents.UpdateEventJSON(ctx, txn, newEvent)
+	})
+	return err
+}
+
+// fetchStateEvents converts the set of event IDs into a set of events. It will fetch any which are missing from the database.
+// Returns a map of room ID to list of events.
+func (d *Database) fetchStateEvents(
+	ctx context.Context, txn *sql.Tx,
+	roomIDToEventIDSet map[string]map[string]bool,
+	eventIDToEvent map[string]types.StreamEvent,
+) (map[string][]types.StreamEvent, error) {
+	stateBetween := make(map[string][]types.StreamEvent)
+	missingEvents := make(map[string][]string)
+	for roomID, ids := range roomIDToEventIDSet {
+		events := stateBetween[roomID]
+		for id, need := range ids {
+			if !need {
+				continue // deleted state
+			}
+			e, ok := eventIDToEvent[id]
+			if ok {
+				events = append(events, e)
+			} else {
+				m := missingEvents[roomID]
+				m = append(m, id)
+				missingEvents[roomID] = m
+			}
+		}
+		stateBetween[roomID] = events
+	}
+
+	if len(missingEvents) > 0 {
+		// This happens when add_state_ids has an event ID which is not in the provided range.
+		// We need to explicitly fetch them.
+		allMissingEventIDs := []string{}
+		for _, missingEvIDs := range missingEvents {
+			allMissingEventIDs = append(allMissingEventIDs, missingEvIDs...)
+		}
+		evs, err := d.fetchMissingStateEvents(ctx, txn, allMissingEventIDs)
+		if err != nil {
+			return nil, err
+		}
+		// we know we got them all otherwise an error would've been returned, so just loop the events
+		for _, ev := range evs {
+			roomID := ev.RoomID()
+			stateBetween[roomID] = append(stateBetween[roomID], ev)
+		}
+	}
+	return stateBetween, nil
+}
+
+func (d *Database) fetchMissingStateEvents(
+	ctx context.Context, txn *sql.Tx, eventIDs []string,
+) ([]types.StreamEvent, error) {
+	// Fetch from the events table first so we pick up the stream ID for the
+	// event.
+	events, err := d.OutputEvents.SelectEvents(ctx, txn, eventIDs, nil, false)
+	if err != nil {
+		return nil, err
+	}
+
+	have := map[string]bool{}
+	for _, event := range events {
+		have[event.EventID()] = true
+	}
+	var missing []string
+	for _, eventID := range eventIDs {
+		if !have[eventID] {
+			missing = append(missing, eventID)
+		}
+	}
+	if len(missing) == 0 {
+		return events, nil
+	}
+
+	// If they are missing from the events table then they should be state
+	// events that we received from outside the main event stream.
+	// These should be in the room state table.
+	stateEvents, err := d.CurrentRoomState.SelectEventsWithEventIDs(ctx, txn, missing)
+
+	if err != nil {
+		return nil, err
+	}
+	if len(stateEvents) != len(missing) {
+		logrus.WithContext(ctx).Warnf("Failed to map all event IDs to events (got %d, wanted %d)", len(stateEvents), len(missing))
+
+		// TODO: Why is this happening? It's probably the roomserver. Uncomment
+		// this error again when we work out what it is and fix it, otherwise we
+		// just end up returning lots of 500s to the client and that breaks
+		// pretty much everything, rather than just sending what we have.
+		//return nil, fmt.Errorf("failed to map all event IDs to events: (got %d, wanted %d)", len(stateEvents), len(missing))
+	}
+	events = append(events, stateEvents...)
+	return events, nil
+}
+
+func (d *Database) StoreNewSendForDeviceMessage(
+	ctx context.Context, userID, deviceID string, event gomatrixserverlib.SendToDeviceEvent,
+) (newPos types.StreamPosition, err error) {
+	j, err := json.Marshal(event)
+	if err != nil {
+		return 0, err
+	}
+	// Delegate the database write task to the SendToDeviceWriter. It'll guarantee
+	// that we don't lock the table for writes in more than one place.
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		newPos, err = d.SendToDevice.InsertSendToDeviceMessage(
+			ctx, txn, userID, deviceID, string(j),
+		)
+		return err
+	})
+	if err != nil {
+		return 0, err
+	}
+	return newPos, nil
+}
+
+func (d *Database) CleanSendToDeviceUpdates(
+	ctx context.Context,
+	userID, deviceID string, before types.StreamPosition,
+) (err error) {
+	if err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.SendToDevice.DeleteSendToDeviceMessages(ctx, txn, userID, deviceID, before)
+	}); err != nil {
+		logrus.WithError(err).Errorf("Failed to clean up old send-to-device messages for user %q device %q", userID, deviceID)
+		return err
+	}
+	return nil
+}
+
+// getMembershipFromEvent returns the value of content.membership iff the event is a state event
+// with type 'm.room.member' and state_key of userID. Otherwise, an empty string is returned.
+func getMembershipFromEvent(ev *gomatrixserverlib.Event, userID string) (string, string) {
+	if ev.Type() != "m.room.member" || !ev.StateKeyEquals(userID) {
+		return "", ""
+	}
+	membership, err := ev.Membership()
+	if err != nil {
+		return "", ""
+	}
+	prevMembership := gjson.GetBytes(ev.Unsigned(), "prev_content.membership").Str
+	return membership, prevMembership
+}
+
+// StoreReceipt stores user receipts
+func (d *Database) StoreReceipt(ctx context.Context, roomId, receiptType, userId, eventId string, timestamp gomatrixserverlib.Timestamp) (pos types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		pos, err = d.Receipts.UpsertReceipt(ctx, txn, roomId, receiptType, userId, eventId, timestamp)
+		return err
+	})
+	return
+}
+
+func (d *Database) UpsertRoomUnreadNotificationCounts(ctx context.Context, userID, roomID string, notificationCount, highlightCount int) (pos types.StreamPosition, err error) {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		pos, err = d.NotificationData.UpsertRoomUnreadCounts(ctx, txn, userID, roomID, notificationCount, highlightCount)
+		return err
+	})
+	return
+}
+
+func (d *Database) SelectContextEvent(ctx context.Context, roomID, eventID string) (int, gomatrixserverlib.HeaderedEvent, error) {
+	return d.OutputEvents.SelectContextEvent(ctx, nil, roomID, eventID)
+}
+
+func (d *Database) SelectContextBeforeEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) ([]*gomatrixserverlib.HeaderedEvent, error) {
+	return d.OutputEvents.SelectContextBeforeEvent(ctx, nil, id, roomID, filter)
+}
+func (d *Database) SelectContextAfterEvent(ctx context.Context, id int, roomID string, filter *gomatrixserverlib.RoomEventFilter) (int, []*gomatrixserverlib.HeaderedEvent, error) {
+	return d.OutputEvents.SelectContextAfterEvent(ctx, nil, id, roomID, filter)
+}
+
+func (d *Database) IgnoresForUser(ctx context.Context, userID string) (*types.IgnoredUsers, error) {
+	return d.Ignores.SelectIgnores(ctx, nil, userID)
+}
+
+func (d *Database) UpdateIgnoresForUser(ctx context.Context, userID string, ignores *types.IgnoredUsers) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.Ignores.UpsertIgnores(ctx, txn, userID, ignores)
+	})
+}
+
+func (d *Database) UpdatePresence(ctx context.Context, userID string, presence types.Presence, statusMsg *string, lastActiveTS gomatrixserverlib.Timestamp, fromSync bool) (types.StreamPosition, error) {
+	var pos types.StreamPosition
+	var err error
+	_ = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		pos, err = d.Presence.UpsertPresence(ctx, txn, userID, statusMsg, presence, lastActiveTS, fromSync)
+		return nil
+	})
+	return pos, err
+}
+
+func (d *Database) GetPresence(ctx context.Context, userID string) (*types.PresenceInternal, error) {
+	return d.Presence.GetPresenceForUser(ctx, nil, userID)
+}
+
+func (d *Database) SelectMembershipForUser(ctx context.Context, roomID, userID string, pos int64) (membership string, topologicalPos int, err error) {
+	return d.Memberships.SelectMembershipForUser(ctx, nil, roomID, userID, pos)
+}
+
+func (s *Database) ReIndex(ctx context.Context, limit, afterID int64) (map[int64]gomatrixserverlib.HeaderedEvent, error) {
+	return s.OutputEvents.ReIndex(ctx, nil, limit, afterID, []string{
+		gomatrixserverlib.MRoomName,
+		gomatrixserverlib.MRoomTopic,
+		"m.room.message",
+	})
+}

syncapi/storage/shared/storage_sync.go

@@ -0,0 +1,574 @@
+package shared
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal/eventutil"
+	"github.com/matrix-org/dendrite/syncapi/types"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+type DatabaseTransaction struct {
+	*Database
+	txn *sql.Tx
+}
+
+func (d *DatabaseTransaction) Commit() error {
+	if d.txn == nil {
+		return nil
+	}
+	return d.txn.Commit()
+}
+
+func (d *DatabaseTransaction) Rollback() error {
+	if d.txn == nil {
+		return nil
+	}
+	return d.txn.Rollback()
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForPDUs(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.OutputEvents.SelectMaxEventID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.OutputEvents.SelectMaxEventID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForReceipts(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.Receipts.SelectMaxReceiptID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.Receipts.SelectMaxReceiptID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForInvites(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.Invites.SelectMaxInviteID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.Invites.SelectMaxInviteID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForSendToDeviceMessages(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.SendToDevice.SelectMaxSendToDeviceMessageID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.SendToDevice.SelectMaxSendToDeviceMessageID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForAccountData(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.AccountData.SelectMaxAccountDataID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.Invites.SelectMaxAccountDataID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForNotificationData(ctx context.Context) (types.StreamPosition, error) {
+	id, err := d.NotificationData.SelectMaxID(ctx, d.txn)
+	if err != nil {
+		return 0, fmt.Errorf("d.NotificationData.SelectMaxID: %w", err)
+	}
+	return types.StreamPosition(id), nil
+}
+
+func (d *DatabaseTransaction) CurrentState(ctx context.Context, roomID string, stateFilterPart *gomatrixserverlib.StateFilter, excludeEventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error) {
+	return d.CurrentRoomState.SelectCurrentState(ctx, d.txn, roomID, stateFilterPart, excludeEventIDs)
+}
+
+func (d *DatabaseTransaction) RoomIDsWithMembership(ctx context.Context, userID string, membership string) ([]string, error) {
+	return d.CurrentRoomState.SelectRoomIDsWithMembership(ctx, d.txn, userID, membership)
+}
+
+func (d *DatabaseTransaction) MembershipCount(ctx context.Context, roomID, membership string, pos types.StreamPosition) (int, error) {
+	return d.Memberships.SelectMembershipCount(ctx, d.txn, roomID, membership, pos)
+}
+
+func (d *DatabaseTransaction) GetRoomHeroes(ctx context.Context, roomID, userID string, memberships []string) ([]string, error) {
+	return d.Memberships.SelectHeroes(ctx, d.txn, roomID, userID, memberships)
+}
+
+func (d *DatabaseTransaction) RecentEvents(ctx context.Context, roomID string, r types.Range, eventFilter *gomatrixserverlib.RoomEventFilter, chronologicalOrder bool, onlySyncEvents bool) ([]types.StreamEvent, bool, error) {
+	return d.OutputEvents.SelectRecentEvents(ctx, d.txn, roomID, r, eventFilter, chronologicalOrder, onlySyncEvents)
+}
+
+func (d *DatabaseTransaction) PositionInTopology(ctx context.Context, eventID string) (pos types.StreamPosition, spos types.StreamPosition, err error) {
+	return d.Topology.SelectPositionInTopology(ctx, d.txn, eventID)
+}
+
+func (d *DatabaseTransaction) InviteEventsInRange(ctx context.Context, targetUserID string, r types.Range) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, types.StreamPosition, error) {
+	return d.Invites.SelectInviteEventsInRange(ctx, d.txn, targetUserID, r)
+}
+
+func (d *DatabaseTransaction) PeeksInRange(ctx context.Context, userID, deviceID string, r types.Range) (peeks []types.Peek, err error) {
+	return d.Peeks.SelectPeeksInRange(ctx, d.txn, userID, deviceID, r)
+}
+
+func (d *DatabaseTransaction) RoomReceiptsAfter(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) (types.StreamPosition, []types.OutputReceiptEvent, error) {
+	return d.Receipts.SelectRoomReceiptsAfter(ctx, d.txn, roomIDs, streamPos)
+}
+
+// Events lookups a list of event by their event ID.
+// Returns a list of events matching the requested IDs found in the database.
+// If an event is not found in the database then it will be omitted from the list.
+// Returns an error if there was a problem talking with the database.
+// Does not include any transaction IDs in the returned events.
+func (d *DatabaseTransaction) Events(ctx context.Context, eventIDs []string) ([]*gomatrixserverlib.HeaderedEvent, error) {
+	streamEvents, err := d.OutputEvents.SelectEvents(ctx, d.txn, eventIDs, nil, false)
+	if err != nil {
+		return nil, err
+	}
+
+	// We don't include a device here as we only include transaction IDs in
+	// incremental syncs.
+	return d.StreamEventsToEvents(nil, streamEvents), nil
+}
+
+func (d *DatabaseTransaction) AllJoinedUsersInRooms(ctx context.Context) (map[string][]string, error) {
+	return d.CurrentRoomState.SelectJoinedUsers(ctx, d.txn)
+}
+
+func (d *DatabaseTransaction) AllJoinedUsersInRoom(ctx context.Context, roomIDs []string) (map[string][]string, error) {
+	return d.CurrentRoomState.SelectJoinedUsersInRoom(ctx, d.txn, roomIDs)
+}
+
+func (d *DatabaseTransaction) AllPeekingDevicesInRooms(ctx context.Context) (map[string][]types.PeekingDevice, error) {
+	return d.Peeks.SelectPeekingDevices(ctx, d.txn)
+}
+
+func (d *DatabaseTransaction) SharedUsers(ctx context.Context, userID string, otherUserIDs []string) ([]string, error) {
+	return d.CurrentRoomState.SelectSharedUsers(ctx, d.txn, userID, otherUserIDs)
+}
+
+func (d *DatabaseTransaction) GetStateEvent(
+	ctx context.Context, roomID, evType, stateKey string,
+) (*gomatrixserverlib.HeaderedEvent, error) {
+	return d.CurrentRoomState.SelectStateEvent(ctx, d.txn, roomID, evType, stateKey)
+}
+
+func (d *DatabaseTransaction) GetStateEventsForRoom(
+	ctx context.Context, roomID string, stateFilter *gomatrixserverlib.StateFilter,
+) (stateEvents []*gomatrixserverlib.HeaderedEvent, err error) {
+	stateEvents, err = d.CurrentRoomState.SelectCurrentState(ctx, d.txn, roomID, stateFilter, nil)
+	return
+}
+
+// GetAccountDataInRange returns all account data for a given user inserted or
+// updated between two given positions
+// Returns a map following the format data[roomID] = []dataTypes
+// If no data is retrieved, returns an empty map
+// If there was an issue with the retrieval, returns an error
+func (d *DatabaseTransaction) GetAccountDataInRange(
+	ctx context.Context, userID string, r types.Range,
+	accountDataFilterPart *gomatrixserverlib.EventFilter,
+) (map[string][]string, types.StreamPosition, error) {
+	return d.AccountData.SelectAccountDataInRange(ctx, d.txn, userID, r, accountDataFilterPart)
+}
+
+func (d *DatabaseTransaction) GetEventsInTopologicalRange(
+	ctx context.Context,
+	from, to *types.TopologyToken,
+	roomID string,
+	filter *gomatrixserverlib.RoomEventFilter,
+	backwardOrdering bool,
+) (events []types.StreamEvent, err error) {
+	var minDepth, maxDepth, maxStreamPosForMaxDepth types.StreamPosition
+	if backwardOrdering {
+		// Backward ordering means the 'from' token has a higher depth than the 'to' token
+		minDepth = to.Depth
+		maxDepth = from.Depth
+		// for cases where we have say 5 events with the same depth, the TopologyToken needs to
+		// know which of the 5 the client has seen. This is done by using the PDU position.
+		// Events with the same maxDepth but less than this PDU position will be returned.
+		maxStreamPosForMaxDepth = from.PDUPosition
+	} else {
+		// Forward ordering means the 'from' token has a lower depth than the 'to' token.
+		minDepth = from.Depth
+		maxDepth = to.Depth
+	}
+
+	// Select the event IDs from the defined range.
+	var eIDs []string
+	eIDs, err = d.Topology.SelectEventIDsInRange(
+		ctx, d.txn, roomID, minDepth, maxDepth, maxStreamPosForMaxDepth, filter.Limit, !backwardOrdering,
+	)
+	if err != nil {
+		return
+	}
+
+	// Retrieve the events' contents using their IDs.
+	events, err = d.OutputEvents.SelectEvents(ctx, d.txn, eIDs, filter, true)
+	return
+}
+
+func (d *DatabaseTransaction) BackwardExtremitiesForRoom(
+	ctx context.Context, roomID string,
+) (backwardExtremities map[string][]string, err error) {
+	return d.BackwardExtremities.SelectBackwardExtremitiesForRoom(ctx, d.txn, roomID)
+}
+
+func (d *DatabaseTransaction) MaxTopologicalPosition(
+	ctx context.Context, roomID string,
+) (types.TopologyToken, error) {
+	depth, streamPos, err := d.Topology.SelectMaxPositionInTopology(ctx, d.txn, roomID)
+	if err != nil {
+		return types.TopologyToken{}, err
+	}
+	return types.TopologyToken{Depth: depth, PDUPosition: streamPos}, nil
+}
+
+func (d *DatabaseTransaction) EventPositionInTopology(
+	ctx context.Context, eventID string,
+) (types.TopologyToken, error) {
+	depth, stream, err := d.Topology.SelectPositionInTopology(ctx, d.txn, eventID)
+	if err != nil {
+		return types.TopologyToken{}, err
+	}
+	return types.TopologyToken{Depth: depth, PDUPosition: stream}, nil
+}
+
+func (d *DatabaseTransaction) StreamToTopologicalPosition(
+	ctx context.Context, roomID string, streamPos types.StreamPosition, backwardOrdering bool,
+) (types.TopologyToken, error) {
+	topoPos, err := d.Topology.SelectStreamToTopologicalPosition(ctx, d.txn, roomID, streamPos, backwardOrdering)
+	switch {
+	case err == sql.ErrNoRows && backwardOrdering: // no events in range, going backward
+		return types.TopologyToken{PDUPosition: streamPos}, nil
+	case err == sql.ErrNoRows && !backwardOrdering: // no events in range, going forward
+		topoPos, streamPos, err = d.Topology.SelectMaxPositionInTopology(ctx, d.txn, roomID)
+		if err != nil {
+			return types.TopologyToken{}, fmt.Errorf("d.Topology.SelectMaxPositionInTopology: %w", err)
+		}
+		return types.TopologyToken{Depth: topoPos, PDUPosition: streamPos}, nil
+	case err != nil: // some other error happened
+		return types.TopologyToken{}, fmt.Errorf("d.Topology.SelectStreamToTopologicalPosition: %w", err)
+	default:
+		return types.TopologyToken{Depth: topoPos, PDUPosition: streamPos}, nil
+	}
+}
+
+// GetBackwardTopologyPos retrieves the backward topology position, i.e. the position of the
+// oldest event in the room's topology.
+func (d *DatabaseTransaction) GetBackwardTopologyPos(
+	ctx context.Context,
+	events []types.StreamEvent,
+) (types.TopologyToken, error) {
+	zeroToken := types.TopologyToken{}
+	if len(events) == 0 {
+		return zeroToken, nil
+	}
+	pos, spos, err := d.Topology.SelectPositionInTopology(ctx, d.txn, events[0].EventID())
+	if err != nil {
+		return zeroToken, err
+	}
+	tok := types.TopologyToken{Depth: pos, PDUPosition: spos}
+	tok.Decrement()
+	return tok, nil
+}
+
+// GetStateDeltas returns the state deltas between fromPos and toPos,
+// exclusive of oldPos, inclusive of newPos, for the rooms in which
+// the user has new membership events.
+// A list of joined room IDs is also returned in case the caller needs it.
+func (d *DatabaseTransaction) GetStateDeltas(
+	ctx context.Context, device *userapi.Device,
+	r types.Range, userID string,
+	stateFilter *gomatrixserverlib.StateFilter,
+) (deltas []types.StateDelta, joinedRoomsIDs []string, err error) {
+	// Implement membership change algorithm: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L821
+	// - Get membership list changes for this user in this sync response
+	// - For each room which has membership list changes:
+	//     * Check if the room is 'newly joined' (insufficient to just check for a join event because we allow dupe joins TODO).
+	//       If it is, then we need to send the full room state down (and 'limited' is always true).
+	//     * Check if user is still CURRENTLY invited to the room. If so, add room to 'invited' block.
+	//     * Check if the user is CURRENTLY (TODO) left/banned. If so, add room to 'archived' block.
+	// - Get all CURRENTLY joined rooms, and add them to 'joined' block.
+
+	// Look up all memberships for the user. We only care about rooms that a
+	// user has ever interacted with — joined to, kicked/banned from, left.
+	memberships, err := d.CurrentRoomState.SelectRoomIDsWithAnyMembership(ctx, d.txn, userID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+
+	allRoomIDs := make([]string, 0, len(memberships))
+	joinedRoomIDs := make([]string, 0, len(memberships))
+	for roomID, membership := range memberships {
+		allRoomIDs = append(allRoomIDs, roomID)
+		if membership == gomatrixserverlib.Join {
+			joinedRoomIDs = append(joinedRoomIDs, roomID)
+		}
+	}
+
+	// get all the state events ever (i.e. for all available rooms) between these two positions
+	stateNeeded, eventMap, err := d.OutputEvents.SelectStateInRange(ctx, d.txn, r, stateFilter, allRoomIDs)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+	state, err := d.fetchStateEvents(ctx, d.txn, stateNeeded, eventMap)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+
+	// find out which rooms this user is peeking, if any.
+	// We do this before joins so any peeks get overwritten
+	peeks, err := d.Peeks.SelectPeeksInRange(ctx, d.txn, userID, device.ID, r)
+	if err != nil && err != sql.ErrNoRows {
+		return nil, nil, err
+	}
+
+	// add peek blocks
+	for _, peek := range peeks {
+		if peek.New {
+			// send full room state down instead of a delta
+			var s []types.StreamEvent
+			s, err = d.currentStateStreamEventsForRoom(ctx, peek.RoomID, stateFilter)
+			if err != nil {
+				if err == sql.ErrNoRows {
+					continue
+				}
+				return nil, nil, err
+			}
+			state[peek.RoomID] = s
+		}
+		if !peek.Deleted {
+			deltas = append(deltas, types.StateDelta{
+				Membership:  gomatrixserverlib.Peek,
+				StateEvents: d.StreamEventsToEvents(device, state[peek.RoomID]),
+				RoomID:      peek.RoomID,
+			})
+		}
+	}
+
+	// handle newly joined rooms and non-joined rooms
+	newlyJoinedRooms := make(map[string]bool, len(state))
+	for roomID, stateStreamEvents := range state {
+		for _, ev := range stateStreamEvents {
+			if membership, prevMembership := getMembershipFromEvent(ev.Event, userID); membership != "" {
+				if membership == gomatrixserverlib.Join && prevMembership != membership {
+					// send full room state down instead of a delta
+					var s []types.StreamEvent
+					s, err = d.currentStateStreamEventsForRoom(ctx, roomID, stateFilter)
+					if err != nil {
+						if err == sql.ErrNoRows {
+							continue
+						}
+						return nil, nil, err
+					}
+					state[roomID] = s
+					newlyJoinedRooms[roomID] = true
+					continue // we'll add this room in when we do joined rooms
+				}
+
+				deltas = append(deltas, types.StateDelta{
+					Membership:    membership,
+					MembershipPos: ev.StreamPosition,
+					StateEvents:   d.StreamEventsToEvents(device, stateStreamEvents),
+					RoomID:        roomID,
+				})
+				break
+			}
+		}
+	}
+
+	// Add in currently joined rooms
+	for _, joinedRoomID := range joinedRoomIDs {
+		deltas = append(deltas, types.StateDelta{
+			Membership:  gomatrixserverlib.Join,
+			StateEvents: d.StreamEventsToEvents(device, state[joinedRoomID]),
+			RoomID:      joinedRoomID,
+			NewlyJoined: newlyJoinedRooms[joinedRoomID],
+		})
+	}
+
+	return deltas, joinedRoomIDs, nil
+}
+
+// GetStateDeltasForFullStateSync is a variant of getStateDeltas used for /sync
+// requests with full_state=true.
+// Fetches full state for all joined rooms and uses selectStateInRange to get
+// updates for other rooms.
+func (d *DatabaseTransaction) GetStateDeltasForFullStateSync(
+	ctx context.Context, device *userapi.Device,
+	r types.Range, userID string,
+	stateFilter *gomatrixserverlib.StateFilter,
+) ([]types.StateDelta, []string, error) {
+	// Look up all memberships for the user. We only care about rooms that a
+	// user has ever interacted with — joined to, kicked/banned from, left.
+	memberships, err := d.CurrentRoomState.SelectRoomIDsWithAnyMembership(ctx, d.txn, userID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+
+	allRoomIDs := make([]string, 0, len(memberships))
+	joinedRoomIDs := make([]string, 0, len(memberships))
+	for roomID, membership := range memberships {
+		allRoomIDs = append(allRoomIDs, roomID)
+		if membership == gomatrixserverlib.Join {
+			joinedRoomIDs = append(joinedRoomIDs, roomID)
+		}
+	}
+
+	// Use a reasonable initial capacity
+	deltas := make(map[string]types.StateDelta)
+
+	peeks, err := d.Peeks.SelectPeeksInRange(ctx, d.txn, userID, device.ID, r)
+	if err != nil && err != sql.ErrNoRows {
+		return nil, nil, err
+	}
+
+	// Add full states for all peeking rooms
+	for _, peek := range peeks {
+		if !peek.Deleted {
+			s, stateErr := d.currentStateStreamEventsForRoom(ctx, peek.RoomID, stateFilter)
+			if stateErr != nil {
+				if stateErr == sql.ErrNoRows {
+					continue
+				}
+				return nil, nil, stateErr
+			}
+			deltas[peek.RoomID] = types.StateDelta{
+				Membership:  gomatrixserverlib.Peek,
+				StateEvents: d.StreamEventsToEvents(device, s),
+				RoomID:      peek.RoomID,
+			}
+		}
+	}
+
+	// Get all the state events ever between these two positions
+	stateNeeded, eventMap, err := d.OutputEvents.SelectStateInRange(ctx, d.txn, r, stateFilter, allRoomIDs)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+	state, err := d.fetchStateEvents(ctx, d.txn, stateNeeded, eventMap)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil, nil
+		}
+		return nil, nil, err
+	}
+
+	for roomID, stateStreamEvents := range state {
+		for _, ev := range stateStreamEvents {
+			if membership, _ := getMembershipFromEvent(ev.Event, userID); membership != "" {
+				if membership != gomatrixserverlib.Join { // We've already added full state for all joined rooms above.
+					deltas[roomID] = types.StateDelta{
+						Membership:    membership,
+						MembershipPos: ev.StreamPosition,
+						StateEvents:   d.StreamEventsToEvents(device, stateStreamEvents),
+						RoomID:        roomID,
+					}
+				}
+
+				break
+			}
+		}
+	}
+
+	// Add full states for all joined rooms
+	for _, joinedRoomID := range joinedRoomIDs {
+		s, stateErr := d.currentStateStreamEventsForRoom(ctx, joinedRoomID, stateFilter)
+		if stateErr != nil {
+			if stateErr == sql.ErrNoRows {
+				continue
+			}
+			return nil, nil, stateErr
+		}
+		deltas[joinedRoomID] = types.StateDelta{
+			Membership:  gomatrixserverlib.Join,
+			StateEvents: d.StreamEventsToEvents(device, s),
+			RoomID:      joinedRoomID,
+		}
+	}
+
+	// Create a response array.
+	result := make([]types.StateDelta, len(deltas))
+	i := 0
+	for _, delta := range deltas {
+		result[i] = delta
+		i++
+	}
+
+	return result, joinedRoomIDs, nil
+}
+
+func (d *DatabaseTransaction) currentStateStreamEventsForRoom(
+	ctx context.Context, roomID string,
+	stateFilter *gomatrixserverlib.StateFilter,
+) ([]types.StreamEvent, error) {
+	allState, err := d.CurrentRoomState.SelectCurrentState(ctx, d.txn, roomID, stateFilter, nil)
+	if err != nil {
+		return nil, err
+	}
+	s := make([]types.StreamEvent, len(allState))
+	for i := 0; i < len(s); i++ {
+		s[i] = types.StreamEvent{HeaderedEvent: allState[i], StreamPosition: 0}
+	}
+	return s, nil
+}
+
+func (d *DatabaseTransaction) SendToDeviceUpdatesForSync(
+	ctx context.Context,
+	userID, deviceID string,
+	from, to types.StreamPosition,
+) (types.StreamPosition, []types.SendToDeviceEvent, error) {
+	// First of all, get our send-to-device updates for this user.
+	lastPos, events, err := d.SendToDevice.SelectSendToDeviceMessages(ctx, d.txn, userID, deviceID, from, to)
+	if err != nil {
+		return from, nil, fmt.Errorf("d.SendToDevice.SelectSendToDeviceMessages: %w", err)
+	}
+	// If there's nothing to do then stop here.
+	if len(events) == 0 {
+		return to, nil, nil
+	}
+	return lastPos, events, nil
+}
+
+func (d *DatabaseTransaction) GetRoomReceipts(ctx context.Context, roomIDs []string, streamPos types.StreamPosition) ([]types.OutputReceiptEvent, error) {
+	_, receipts, err := d.Receipts.SelectRoomReceiptsAfter(ctx, d.txn, roomIDs, streamPos)
+	return receipts, err
+}
+
+func (d *DatabaseTransaction) GetUserUnreadNotificationCountsForRooms(ctx context.Context, userID string, rooms map[string]string) (map[string]*eventutil.NotificationData, error) {
+	roomIDs := make([]string, 0, len(rooms))
+	for roomID, membership := range rooms {
+		if membership != gomatrixserverlib.Join {
+			continue
+		}
+		roomIDs = append(roomIDs, roomID)
+	}
+	return d.NotificationData.SelectUserUnreadCountsForRooms(ctx, d.txn, userID, roomIDs)
+}
+
+func (d *DatabaseTransaction) GetPresence(ctx context.Context, userID string) (*types.PresenceInternal, error) {
+	return d.Presence.GetPresenceForUser(ctx, d.txn, userID)
+}
+
+func (d *DatabaseTransaction) PresenceAfter(ctx context.Context, after types.StreamPosition, filter gomatrixserverlib.EventFilter) (map[string]*types.PresenceInternal, error) {
+	return d.Presence.GetPresenceAfter(ctx, d.txn, after, filter)
+}
+
+func (d *DatabaseTransaction) MaxStreamPositionForPresence(ctx context.Context) (types.StreamPosition, error) {
+	return d.Presence.GetMaxPresenceID(ctx, d.txn)
+}

syncapi/storage/sqlite3/current_room_state_table.go

@@ -367,7 +367,13 @@ func (s *currentRoomStateStatements) SelectEventsWithEventIDs(
 	for start < len(eventIDs) {
 		n := minOfInts(len(eventIDs)-start, 999)
 		query := strings.Replace(selectEventsWithEventIDsSQL, "($1)", sqlutil.QueryVariadic(n), 1)
-		rows, err := txn.QueryContext(ctx, query, iEventIDs[start:start+n]...)
+		var rows *sql.Rows
+		var err error
+		if txn == nil {
+			rows, err = s.db.QueryContext(ctx, query, iEventIDs[start:start+n]...)
+		} else {
+			rows, err = txn.QueryContext(ctx, query, iEventIDs[start:start+n]...)
+		}
 		if err != nil {
 			return nil, err
 		}

syncapi/storage/sqlite3/invites_table.go

@@ -50,7 +50,7 @@ const deleteInviteEventSQL = "" +
 	"UPDATE syncapi_invite_events SET deleted=true, id=$1 WHERE event_id = $2 AND deleted=false"
 
 const selectInviteEventsInRangeSQL = "" +
-	"SELECT room_id, headered_event_json, deleted FROM syncapi_invite_events" +
+	"SELECT id, room_id, headered_event_json, deleted FROM syncapi_invite_events" +
 	" WHERE target_user_id = $1 AND id > $2 AND id <= $3" +
 	" ORDER BY id DESC"
 
@@ -132,23 +132,28 @@ func (s *inviteEventsStatements) DeleteInviteEvent(
 // active invites for the target user ID in the supplied range.
 func (s *inviteEventsStatements) SelectInviteEventsInRange(
 	ctx context.Context, txn *sql.Tx, targetUserID string, r types.Range,
-) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, error) {
+) (map[string]*gomatrixserverlib.HeaderedEvent, map[string]*gomatrixserverlib.HeaderedEvent, types.StreamPosition, error) {
+	var lastPos types.StreamPosition
 	stmt := sqlutil.TxStmt(txn, s.selectInviteEventsInRangeStmt)
 	rows, err := stmt.QueryContext(ctx, targetUserID, r.Low(), r.High())
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, lastPos, err
 	}
 	defer internal.CloseAndLogIfError(ctx, rows, "selectInviteEventsInRange: rows.close() failed")
 	result := map[string]*gomatrixserverlib.HeaderedEvent{}
 	retired := map[string]*gomatrixserverlib.HeaderedEvent{}
 	for rows.Next() {
 		var (
+			id        types.StreamPosition
 			roomID    string
 			eventJSON []byte
 			deleted   bool
 		)
-		if err = rows.Scan(&roomID, &eventJSON, &deleted); err != nil {
+		if err = rows.Scan(&id, &roomID, &eventJSON, &deleted); err != nil {
-			return nil, nil, err
+			return nil, nil, lastPos, err
+		}
+		if id > lastPos {
+			lastPos = id
 		}
 
 		// if we have seen this room before, it has a higher stream position and hence takes priority
@@ -161,15 +166,19 @@ func (s *inviteEventsStatements) SelectInviteEventsInRange(
 
 		var event *gomatrixserverlib.HeaderedEvent
 		if err := json.Unmarshal(eventJSON, &event); err != nil {
-			return nil, nil, err
+			return nil, nil, lastPos, err
 		}
+
 		if deleted {
 			retired[roomID] = event
 		} else {
 			result[roomID] = event
 		}
 	}
-	return result, retired, nil
+	if lastPos == 0 {
+		lastPos = r.To
+	}
+	return result, retired, lastPos, nil
 }
 
 func (s *inviteEventsStatements) SelectMaxInviteID(

syncapi/storage/sqlite3/syncserver.go

@@ -49,6 +49,20 @@ func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions)
 	return &d, nil
 }
 
+func (d *SyncServerDatasource) NewDatabaseSnapshot(ctx context.Context) (*shared.DatabaseTransaction, error) {
+	return &shared.DatabaseTransaction{
+		Database: &d.Database,
+		// not setting a transaction because SQLite doesn't support it
+	}, nil
+}
+
+func (d *SyncServerDatasource) NewDatabaseTransaction(ctx context.Context) (*shared.DatabaseTransaction, error) {
+	return &shared.DatabaseTransaction{
+		Database: &d.Database,
+		// not setting a transaction because SQLite doesn't support it
+	}, nil
+}
+
 func (d *SyncServerDatasource) prepare(ctx context.Context) (err error) {
 	if err = d.streamID.Prepare(d.db); err != nil {
 		return err

syncapi/storage/storage_test.go

@@ -60,6 +60,17 @@ func TestWriteEvents(t *testing.T) {
 	})
 }
 
+func WithSnapshot(t *testing.T, db storage.Database, f func(snapshot storage.DatabaseTransaction)) {
+	snapshot, err := db.NewDatabaseSnapshot(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	f(snapshot)
+	if err := snapshot.Rollback(); err != nil {
+		t.Fatal(err)
+	}
+}
+
 // These tests assert basic functionality of RecentEvents for PDUs
 func TestRecentEventsPDU(t *testing.T) {
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
@@ -79,10 +90,13 @@ func TestRecentEventsPDU(t *testing.T) {
 		// dummy room to make sure SQL queries are filtering on room ID
 		MustWriteEvents(t, db, test.NewRoom(t, alice).Events())
 
-		latest, err := db.MaxStreamPositionForPDUs(ctx)
+		var latest types.StreamPosition
-		if err != nil {
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
-			t.Fatalf("failed to get MaxStreamPositionForPDUs: %s", err)
+			var err error
+			if latest, err = snapshot.MaxStreamPositionForPDUs(ctx); err != nil {
+				t.Fatal("failed to get MaxStreamPositionForPDUs: %w", err)
 			}
+		})
 
 		testCases := []struct {
 			Name         string
@@ -140,14 +154,19 @@ func TestRecentEventsPDU(t *testing.T) {
 			tc := testCases[i]
 			t.Run(tc.Name, func(st *testing.T) {
 				var filter gomatrixserverlib.RoomEventFilter
+				var gotEvents []types.StreamEvent
+				var limited bool
 				filter.Limit = tc.Limit
-				gotEvents, limited, err := db.RecentEvents(ctx, r.ID, types.Range{
+				WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
+					var err error
+					gotEvents, limited, err = snapshot.RecentEvents(ctx, r.ID, types.Range{
 						From: tc.From,
 						To:   tc.To,
 					}, &filter, !tc.ReverseOrder, true)
 					if err != nil {
 						st.Fatalf("failed to do sync: %s", err)
 					}
+				})
 				if limited != tc.WantLimited {
 					st.Errorf("got limited=%v want %v", limited, tc.WantLimited)
 				}
@@ -178,7 +197,8 @@ func TestGetEventsInRangeWithTopologyToken(t *testing.T) {
 		events := r.Events()
 		_ = MustWriteEvents(t, db, events)
 
-		from, err := db.MaxTopologicalPosition(ctx, r.ID)
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
+			from, err := snapshot.MaxTopologicalPosition(ctx, r.ID)
 			if err != nil {
 				t.Fatalf("failed to get MaxTopologicalPosition: %s", err)
 			}
@@ -188,13 +208,14 @@ func TestGetEventsInRangeWithTopologyToken(t *testing.T) {
 
 			// backpaginate 5 messages starting at the latest position.
 			filter := &gomatrixserverlib.RoomEventFilter{Limit: 5}
-		paginatedEvents, err := db.GetEventsInTopologicalRange(ctx, &from, &to, r.ID, filter, true)
+			paginatedEvents, err := snapshot.GetEventsInTopologicalRange(ctx, &from, &to, r.ID, filter, true)
 			if err != nil {
 				t.Fatalf("GetEventsInTopologicalRange returned an error: %s", err)
 			}
-		gots := db.StreamEventsToEvents(nil, paginatedEvents)
+			gots := snapshot.StreamEventsToEvents(nil, paginatedEvents)
 			test.AssertEventsEqual(t, gots, test.Reversed(events[len(events)-5:]))
 		})
+	})
 }
 
 /*
@@ -414,13 +435,16 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 		defer closeBase()
 		// At this point there should be no messages. We haven't sent anything
 		// yet.
-		_, events, err := db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, 100)
+
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
+			_, events, err := snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, 100)
 			if err != nil {
 				t.Fatal(err)
 			}
 			if len(events) != 0 {
 				t.Fatal("first call should have no updates")
 			}
+		})
 
 		// Try sending a message.
 		streamPos, err := db.StoreNewSendForDeviceMessage(ctx, alice.ID, deviceID, gomatrixserverlib.SendToDeviceEvent{
@@ -432,10 +456,12 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 			t.Fatal(err)
 		}
 
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
 			// At this point we should get exactly one message. We're sending the sync position
 			// that we were given from the update and the send-to-device update will be updated
 			// in the database to reflect that this was the sync position we sent the message at.
-		streamPos, events, err = db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, streamPos)
+			var events []types.SendToDeviceEvent
+			streamPos, events, err = snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, streamPos)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -446,21 +472,25 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 			// At this point we should still have one message because we haven't progressed the
 			// sync position yet. This is equivalent to the client failing to /sync and retrying
 			// with the same position.
-		streamPos, events, err = db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, streamPos)
+			streamPos, events, err = snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, streamPos)
 			if err != nil {
 				t.Fatal(err)
 			}
 			if len(events) != 1 {
 				t.Fatal("third call should have one update still")
 			}
+		})
+
 		err = db.CleanSendToDeviceUpdates(context.Background(), alice.ID, deviceID, streamPos)
 		if err != nil {
 			return
 		}
 
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
 			// At this point we should now have no updates, because we've progressed the sync
 			// position. Therefore the update from before will not be sent again.
-		_, events, err = db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, streamPos, streamPos+10)
+			var events []types.SendToDeviceEvent
+			_, events, err = snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, streamPos, streamPos+10)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -470,13 +500,14 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 
 			// At this point we should still have no updates, because no new updates have been
 			// sent.
-		_, events, err = db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, streamPos, streamPos+10)
+			_, events, err = snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, streamPos, streamPos+10)
 			if err != nil {
 				t.Fatal(err)
 			}
 			if len(events) != 0 {
 				t.Fatal("fifth call should have no updates")
 			}
+		})
 
 		// Send some more messages and verify the ordering is correct ("in order of arrival")
 		var lastPos types.StreamPosition = 0
@@ -492,7 +523,8 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 			lastPos = streamPos
 		}
 
-		_, events, err = db.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, lastPos)
+		WithSnapshot(t, db, func(snapshot storage.DatabaseTransaction) {
+			_, events, err := snapshot.SendToDeviceUpdatesForSync(ctx, alice.ID, deviceID, 0, lastPos)
 			if err != nil {
 				t.Fatalf("unable to get events: %v", err)
 			}
@@ -505,6 +537,7 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 				}
 			}
 		})
+	})
 }
 
 /*

syncapi/storage/tables/interface.go

@@ -37,7 +37,7 @@ type Invites interface {
 	DeleteInviteEvent(ctx context.Context, txn *sql.Tx, inviteEventID string) (types.StreamPosition, error)
 	// SelectInviteEventsInRange returns a map of room ID to invite events. If multiple invite/retired invites exist in the given range, return the latest value
 	// for the room.
-	SelectInviteEventsInRange(ctx context.Context, txn *sql.Tx, targetUserID string, r types.Range) (invites map[string]*gomatrixserverlib.HeaderedEvent, retired map[string]*gomatrixserverlib.HeaderedEvent, err error)
+	SelectInviteEventsInRange(ctx context.Context, txn *sql.Tx, targetUserID string, r types.Range) (invites map[string]*gomatrixserverlib.HeaderedEvent, retired map[string]*gomatrixserverlib.HeaderedEvent, maxID types.StreamPosition, err error)
 	SelectMaxInviteID(ctx context.Context, txn *sql.Tx) (id int64, err error)
 }
 

syncapi/streams/stream_accountdata.go

@@ -5,22 +5,25 @@ import (
 
 	"github.com/matrix-org/gomatrixserverlib"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 )
 
 type AccountDataStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 	userAPI userapi.SyncUserAPI
 }
 
-func (p *AccountDataStreamProvider) Setup() {
+func (p *AccountDataStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
 	p.latestMutex.Lock()
 	defer p.latestMutex.Unlock()
 
-	id, err := p.DB.MaxStreamPositionForAccountData(context.Background())
+	id, err := snapshot.MaxStreamPositionForAccountData(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -29,13 +32,15 @@ func (p *AccountDataStreamProvider) Setup() {
 
 func (p *AccountDataStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *AccountDataStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
@@ -44,7 +49,7 @@ func (p *AccountDataStreamProvider) IncrementalSync(
 		To:   to,
 	}
 
-	dataTypes, pos, err := p.DB.GetAccountDataInRange(
+	dataTypes, pos, err := snapshot.GetAccountDataInRange(
 		ctx, req.Device.UserID, r, &req.Filter.AccountData,
 	)
 	if err != nil {

syncapi/streams/stream_devicelist.go

@@ -6,17 +6,19 @@ import (
 	keyapi "github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/syncapi/internal"
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
 type DeviceListStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 	rsAPI  api.SyncRoomserverAPI
 	keyAPI keyapi.SyncKeyAPI
 }
 
 func (p *DeviceListStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
 	return p.LatestPosition(ctx)
@@ -24,11 +26,12 @@ func (p *DeviceListStreamProvider) CompleteSync(
 
 func (p *DeviceListStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
 	var err error
-	to, _, err = internal.DeviceListCatchup(context.Background(), p.DB, p.keyAPI, p.rsAPI, req.Device.UserID, req.Response, from, to)
+	to, _, err = internal.DeviceListCatchup(context.Background(), snapshot, p.keyAPI, p.rsAPI, req.Device.UserID, req.Response, from, to)
 	if err != nil {
 		req.Log.WithError(err).Error("internal.DeviceListCatchup failed")
 		return from

syncapi/streams/stream_invite.go

@@ -9,20 +9,23 @@ import (
 
 	"github.com/matrix-org/gomatrixserverlib"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
 type InviteStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 }
 
-func (p *InviteStreamProvider) Setup() {
+func (p *InviteStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
 	p.latestMutex.Lock()
 	defer p.latestMutex.Unlock()
 
-	id, err := p.DB.MaxStreamPositionForInvites(context.Background())
+	id, err := snapshot.MaxStreamPositionForInvites(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -31,13 +34,15 @@ func (p *InviteStreamProvider) Setup() {
 
 func (p *InviteStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *InviteStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
@@ -46,7 +51,7 @@ func (p *InviteStreamProvider) IncrementalSync(
 		To:   to,
 	}
 
-	invites, retiredInvites, err := p.DB.InviteEventsInRange(
+	invites, retiredInvites, maxID, err := snapshot.InviteEventsInRange(
 		ctx, req.Device.UserID, r,
 	)
 	if err != nil {
@@ -86,5 +91,5 @@ func (p *InviteStreamProvider) IncrementalSync(
 		}
 	}
 
-	return to
+	return maxID
 }

syncapi/streams/stream_notificationdata.go

@@ -3,17 +3,23 @@ package streams
 import (
 	"context"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
 type NotificationDataStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 }
 
-func (p *NotificationDataStreamProvider) Setup() {
+func (p *NotificationDataStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
-	id, err := p.DB.MaxStreamPositionForNotificationData(context.Background())
+	p.latestMutex.Lock()
+	defer p.latestMutex.Unlock()
+
+	id, err := snapshot.MaxStreamPositionForNotificationData(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -22,20 +28,22 @@ func (p *NotificationDataStreamProvider) Setup() {
 
 func (p *NotificationDataStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *NotificationDataStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, _ types.StreamPosition,
 ) types.StreamPosition {
 	// Get the unread notifications for rooms in our join response.
 	// This is to ensure clients always have an unread notification section
 	// and can display the correct numbers.
-	countsByRoom, err := p.DB.GetUserUnreadNotificationCountsForRooms(ctx, req.Device.UserID, req.Rooms)
+	countsByRoom, err := snapshot.GetUserUnreadNotificationCountsForRooms(ctx, req.Device.UserID, req.Rooms)
 	if err != nil {
 		req.Log.WithError(err).Error("GetUserUnreadNotificationCountsForRooms failed")
 		return from

syncapi/streams/stream_pdu.go

@@ -5,7 +5,6 @@ import (
 	"database/sql"
 	"fmt"
 	"sort"
-	"sync"
 	"time"
 
 	"github.com/matrix-org/dendrite/internal/caching"
@@ -18,7 +17,6 @@ import (
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/sirupsen/logrus"
 	"github.com/tidwall/gjson"
-	"go.uber.org/atomic"
 
 	"github.com/matrix-org/dendrite/syncapi/notifier"
 )
@@ -33,44 +31,23 @@ const PDU_STREAM_WORKERS = 256
 const PDU_STREAM_QUEUESIZE = PDU_STREAM_WORKERS * 8
 
 type PDUStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 
-	tasks   chan func()
-	workers atomic.Int32
 	// userID+deviceID -> lazy loading cache
 	lazyLoadCache caching.LazyLoadCache
 	rsAPI         roomserverAPI.SyncRoomserverAPI
 	notifier      *notifier.Notifier
 }
 
-func (p *PDUStreamProvider) worker() {
+func (p *PDUStreamProvider) Setup(
-	defer p.workers.Dec()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
-	for {
+) {
-		select {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
-		case f := <-p.tasks:
-			f()
-		case <-time.After(time.Second * 10):
-			return
-		}
-	}
-}
-
-func (p *PDUStreamProvider) queue(f func()) {
-	if p.workers.Load() < PDU_STREAM_WORKERS {
-		p.workers.Inc()
-		go p.worker()
-	}
-	p.tasks <- f
-}
-
-func (p *PDUStreamProvider) Setup() {
-	p.StreamProvider.Setup()
-	p.tasks = make(chan func(), PDU_STREAM_QUEUESIZE)
 
 	p.latestMutex.Lock()
 	defer p.latestMutex.Unlock()
 
-	id, err := p.DB.MaxStreamPositionForPDUs(context.Background())
+	id, err := snapshot.MaxStreamPositionForPDUs(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -79,6 +56,7 @@ func (p *PDUStreamProvider) Setup() {
 
 func (p *PDUStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
 	from := types.StreamPosition(0)
@@ -94,7 +72,7 @@ func (p *PDUStreamProvider) CompleteSync(
 	}
 
 	// Extract room state and recent events for all rooms the user is joined to.
-	joinedRoomIDs, err := p.DB.RoomIDsWithMembership(ctx, req.Device.UserID, gomatrixserverlib.Join)
+	joinedRoomIDs, err := snapshot.RoomIDsWithMembership(ctx, req.Device.UserID, gomatrixserverlib.Join)
 	if err != nil {
 		req.Log.WithError(err).Error("p.DB.RoomIDsWithMembership failed")
 		return from
@@ -103,7 +81,7 @@ func (p *PDUStreamProvider) CompleteSync(
 	stateFilter := req.Filter.Room.State
 	eventFilter := req.Filter.Room.Timeline
 
-	if err = p.addIgnoredUsersToFilter(ctx, req, &eventFilter); err != nil {
+	if err = p.addIgnoredUsersToFilter(ctx, snapshot, req, &eventFilter); err != nil {
 		req.Log.WithError(err).Error("unable to update event filter with ignored users")
 	}
 
@@ -117,33 +95,20 @@ func (p *PDUStreamProvider) CompleteSync(
 	}
 
 	// Build up a /sync response. Add joined rooms.
-	var reqMutex sync.Mutex
+	for _, roomID := range joinedRoomIDs {
-	var reqWaitGroup sync.WaitGroup
-	reqWaitGroup.Add(len(joinedRoomIDs))
-	for _, room := range joinedRoomIDs {
-		roomID := room
-		p.queue(func() {
-			defer reqWaitGroup.Done()
-
 		jr, jerr := p.getJoinResponseForCompleteSync(
-				ctx, roomID, r, &stateFilter, &eventFilter, req.WantFullState, req.Device, false,
+			ctx, snapshot, roomID, r, &stateFilter, &eventFilter, req.WantFullState, req.Device, false,
 		)
 		if jerr != nil {
 			req.Log.WithError(jerr).Error("p.getJoinResponseForCompleteSync failed")
-				return
+			continue // return from
 		}
-
-			reqMutex.Lock()
-			defer reqMutex.Unlock()
 		req.Response.Rooms.Join[roomID] = *jr
 		req.Rooms[roomID] = gomatrixserverlib.Join
-		})
 	}
 
-	reqWaitGroup.Wait()
-
 	// Add peeked rooms.
-	peeks, err := p.DB.PeeksInRange(ctx, req.Device.UserID, req.Device.ID, r)
+	peeks, err := snapshot.PeeksInRange(ctx, req.Device.UserID, req.Device.ID, r)
 	if err != nil {
 		req.Log.WithError(err).Error("p.DB.PeeksInRange failed")
 		return from
@@ -152,11 +117,11 @@ func (p *PDUStreamProvider) CompleteSync(
 		if !peek.Deleted {
 			var jr *types.JoinResponse
 			jr, err = p.getJoinResponseForCompleteSync(
-				ctx, peek.RoomID, r, &stateFilter, &eventFilter, req.WantFullState, req.Device, true,
+				ctx, snapshot, peek.RoomID, r, &stateFilter, &eventFilter, req.WantFullState, req.Device, true,
 			)
 			if err != nil {
 				req.Log.WithError(err).Error("p.getJoinResponseForCompleteSync failed")
-				return from
+				continue // return from
 			}
 			req.Response.Rooms.Peek[peek.RoomID] = *jr
 		}
@@ -167,6 +132,7 @@ func (p *PDUStreamProvider) CompleteSync(
 
 func (p *PDUStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) (newPos types.StreamPosition) {
@@ -184,12 +150,12 @@ func (p *PDUStreamProvider) IncrementalSync(
 	eventFilter := req.Filter.Room.Timeline
 
 	if req.WantFullState {
-		if stateDeltas, syncJoinedRooms, err = p.DB.GetStateDeltasForFullStateSync(ctx, req.Device, r, req.Device.UserID, &stateFilter); err != nil {
+		if stateDeltas, syncJoinedRooms, err = snapshot.GetStateDeltasForFullStateSync(ctx, req.Device, r, req.Device.UserID, &stateFilter); err != nil {
 			req.Log.WithError(err).Error("p.DB.GetStateDeltasForFullStateSync failed")
 			return
 		}
 	} else {
-		if stateDeltas, syncJoinedRooms, err = p.DB.GetStateDeltas(ctx, req.Device, r, req.Device.UserID, &stateFilter); err != nil {
+		if stateDeltas, syncJoinedRooms, err = snapshot.GetStateDeltas(ctx, req.Device, r, req.Device.UserID, &stateFilter); err != nil {
 			req.Log.WithError(err).Error("p.DB.GetStateDeltas failed")
 			return
 		}
@@ -203,7 +169,7 @@ func (p *PDUStreamProvider) IncrementalSync(
 		return to
 	}
 
-	if err = p.addIgnoredUsersToFilter(ctx, req, &eventFilter); err != nil {
+	if err = p.addIgnoredUsersToFilter(ctx, snapshot, req, &eventFilter); err != nil {
 		req.Log.WithError(err).Error("unable to update event filter with ignored users")
 	}
 
@@ -222,7 +188,7 @@ func (p *PDUStreamProvider) IncrementalSync(
 			}
 		}
 		var pos types.StreamPosition
-		if pos, err = p.addRoomDeltaToResponse(ctx, req.Device, newRange, delta, &eventFilter, &stateFilter, req.Response); err != nil {
+		if pos, err = p.addRoomDeltaToResponse(ctx, snapshot, req.Device, newRange, delta, &eventFilter, &stateFilter, req.Response); err != nil {
 			req.Log.WithError(err).Error("d.addRoomDeltaToResponse failed")
 			return to
 		}
@@ -244,6 +210,7 @@ func (p *PDUStreamProvider) IncrementalSync(
 // nolint:gocyclo
 func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	device *userapi.Device,
 	r types.Range,
 	delta types.StateDelta,
@@ -260,7 +227,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 		// This is all "okay" assuming history_visibility == "shared" which it is by default.
 		r.To = delta.MembershipPos
 	}
-	recentStreamEvents, limited, err := p.DB.RecentEvents(
+	recentStreamEvents, limited, err := snapshot.RecentEvents(
 		ctx, delta.RoomID, r,
 		eventFilter, true, true,
 	)
@@ -270,9 +237,9 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 		}
 		return r.From, fmt.Errorf("p.DB.RecentEvents: %w", err)
 	}
-	recentEvents := p.DB.StreamEventsToEvents(device, recentStreamEvents)
+	recentEvents := snapshot.StreamEventsToEvents(device, recentStreamEvents)
 	delta.StateEvents = removeDuplicates(delta.StateEvents, recentEvents) // roll back
-	prevBatch, err := p.DB.GetBackwardTopologyPos(ctx, recentStreamEvents)
+	prevBatch, err := snapshot.GetBackwardTopologyPos(ctx, recentStreamEvents)
 	if err != nil {
 		return r.From, fmt.Errorf("p.DB.GetBackwardTopologyPos: %w", err)
 	}
@@ -291,7 +258,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	latestPosition := r.To
 	updateLatestPosition := func(mostRecentEventID string) {
 		var pos types.StreamPosition
-		if _, pos, err = p.DB.PositionInTopology(ctx, mostRecentEventID); err == nil {
+		if _, pos, err = snapshot.PositionInTopology(ctx, mostRecentEventID); err == nil {
 			switch {
 			case r.Backwards && pos < latestPosition:
 				fallthrough
@@ -303,7 +270,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 
 	if stateFilter.LazyLoadMembers {
 		delta.StateEvents, err = p.lazyLoadMembers(
-			ctx, delta.RoomID, true, limited, stateFilter,
+			ctx, snapshot, delta.RoomID, true, limited, stateFilter,
 			device, recentEvents, delta.StateEvents,
 		)
 		if err != nil && err != sql.ErrNoRows {
@@ -320,7 +287,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	}
 
 	// Applies the history visibility rules
-	events, err := applyHistoryVisibilityFilter(ctx, p.DB, p.rsAPI, delta.RoomID, device.UserID, eventFilter.Limit, recentEvents)
+	events, err := applyHistoryVisibilityFilter(ctx, snapshot, p.rsAPI, delta.RoomID, device.UserID, eventFilter.Limit, recentEvents)
 	if err != nil {
 		logrus.WithError(err).Error("unable to apply history visibility filter")
 	}
@@ -336,7 +303,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	case gomatrixserverlib.Join:
 		jr := types.NewJoinResponse()
 		if hasMembershipChange {
-			p.addRoomSummary(ctx, jr, delta.RoomID, device.UserID, latestPosition)
+			p.addRoomSummary(ctx, snapshot, jr, delta.RoomID, device.UserID, latestPosition)
 		}
 		jr.Timeline.PrevBatch = &prevBatch
 		jr.Timeline.Events = gomatrixserverlib.HeaderedToClientEvents(events, gomatrixserverlib.FormatSync)
@@ -376,7 +343,7 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 // sure we always return the required events in the timeline.
 func applyHistoryVisibilityFilter(
 	ctx context.Context,
-	db storage.Database,
+	snapshot storage.DatabaseTransaction,
 	rsAPI roomserverAPI.SyncRoomserverAPI,
 	roomID, userID string,
 	limit int,
@@ -384,7 +351,7 @@ func applyHistoryVisibilityFilter(
 ) ([]*gomatrixserverlib.HeaderedEvent, error) {
 	// We need to make sure we always include the latest states events, if they are in the timeline.
 	// We grep at least limit * 2 events, to ensure we really get the needed events.
-	stateEvents, err := db.CurrentState(ctx, roomID, &gomatrixserverlib.StateFilter{Limit: limit * 2}, nil)
+	stateEvents, err := snapshot.CurrentState(ctx, roomID, &gomatrixserverlib.StateFilter{Limit: limit * 2}, nil)
 	if err != nil {
 		// Not a fatal error, we can continue without the stateEvents,
 		// they are only needed if there are state events in the timeline.
@@ -395,7 +362,7 @@ func applyHistoryVisibilityFilter(
 		alwaysIncludeIDs[ev.EventID()] = struct{}{}
 	}
 	startTime := time.Now()
-	events, err := internal.ApplyHistoryVisibilityFilter(ctx, db, rsAPI, recentEvents, alwaysIncludeIDs, userID, "sync")
+	events, err := internal.ApplyHistoryVisibilityFilter(ctx, snapshot, rsAPI, recentEvents, alwaysIncludeIDs, userID, "sync")
 	if err != nil {
 		return nil, err
 	}
@@ -408,10 +375,10 @@ func applyHistoryVisibilityFilter(
 	return events, nil
 }
 
-func (p *PDUStreamProvider) addRoomSummary(ctx context.Context, jr *types.JoinResponse, roomID, userID string, latestPosition types.StreamPosition) {
+func (p *PDUStreamProvider) addRoomSummary(ctx context.Context, snapshot storage.DatabaseTransaction, jr *types.JoinResponse, roomID, userID string, latestPosition types.StreamPosition) {
 	// Work out how many members are in the room.
-	joinedCount, _ := p.DB.MembershipCount(ctx, roomID, gomatrixserverlib.Join, latestPosition)
+	joinedCount, _ := snapshot.MembershipCount(ctx, roomID, gomatrixserverlib.Join, latestPosition)
-	invitedCount, _ := p.DB.MembershipCount(ctx, roomID, gomatrixserverlib.Invite, latestPosition)
+	invitedCount, _ := snapshot.MembershipCount(ctx, roomID, gomatrixserverlib.Invite, latestPosition)
 
 	jr.Summary.JoinedMemberCount = &joinedCount
 	jr.Summary.InvitedMemberCount = &invitedCount
@@ -439,7 +406,7 @@ func (p *PDUStreamProvider) addRoomSummary(ctx context.Context, jr *types.JoinRe
 			}
 		}
 	}
-	heroes, err := p.DB.GetRoomHeroes(ctx, roomID, userID, []string{"join", "invite"})
+	heroes, err := snapshot.GetRoomHeroes(ctx, roomID, userID, []string{"join", "invite"})
 	if err != nil {
 		return
 	}
@@ -449,6 +416,7 @@ func (p *PDUStreamProvider) addRoomSummary(ctx context.Context, jr *types.JoinRe
 
 func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	roomID string,
 	r types.Range,
 	stateFilter *gomatrixserverlib.StateFilter,
@@ -460,7 +428,7 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 	jr = types.NewJoinResponse()
 	// TODO: When filters are added, we may need to call this multiple times to get enough events.
 	//       See: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L316
-	recentStreamEvents, limited, err := p.DB.RecentEvents(
+	recentStreamEvents, limited, err := snapshot.RecentEvents(
 		ctx, roomID, r, eventFilter, true, true,
 	)
 	if err != nil {
@@ -484,7 +452,7 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 		}
 	}
 
-	stateEvents, err := p.DB.CurrentState(ctx, roomID, stateFilter, excludingEventIDs)
+	stateEvents, err := snapshot.CurrentState(ctx, roomID, stateFilter, excludingEventIDs)
 	if err != nil {
 		return
 	}
@@ -494,7 +462,7 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 	var prevBatch *types.TopologyToken
 	if len(recentStreamEvents) > 0 {
 		var backwardTopologyPos, backwardStreamPos types.StreamPosition
-		backwardTopologyPos, backwardStreamPos, err = p.DB.PositionInTopology(ctx, recentStreamEvents[0].EventID())
+		backwardTopologyPos, backwardStreamPos, err = snapshot.PositionInTopology(ctx, recentStreamEvents[0].EventID())
 		if err != nil {
 			return
 		}
@@ -505,18 +473,18 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 		prevBatch.Decrement()
 	}
 
-	p.addRoomSummary(ctx, jr, roomID, device.UserID, r.From)
+	p.addRoomSummary(ctx, snapshot, jr, roomID, device.UserID, r.From)
 
 	// We don't include a device here as we don't need to send down
 	// transaction IDs for complete syncs, but we do it anyway because Sytest demands it for:
 	// "Can sync a room with a message with a transaction id" - which does a complete sync to check.
-	recentEvents := p.DB.StreamEventsToEvents(device, recentStreamEvents)
+	recentEvents := snapshot.StreamEventsToEvents(device, recentStreamEvents)
 	stateEvents = removeDuplicates(stateEvents, recentEvents)
 
 	events := recentEvents
 	// Only apply history visibility checks if the response is for joined rooms
 	if !isPeek {
-		events, err = applyHistoryVisibilityFilter(ctx, p.DB, p.rsAPI, roomID, device.UserID, eventFilter.Limit, recentEvents)
+		events, err = applyHistoryVisibilityFilter(ctx, snapshot, p.rsAPI, roomID, device.UserID, eventFilter.Limit, recentEvents)
 		if err != nil {
 			logrus.WithError(err).Error("unable to apply history visibility filter")
 		}
@@ -530,7 +498,8 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 		if err != nil {
 			return nil, err
 		}
-		stateEvents, err = p.lazyLoadMembers(ctx, roomID,
+		stateEvents, err = p.lazyLoadMembers(
+			ctx, snapshot, roomID,
 			false, limited, stateFilter,
 			device, recentEvents, stateEvents,
 		)
@@ -549,7 +518,7 @@ func (p *PDUStreamProvider) getJoinResponseForCompleteSync(
 }
 
 func (p *PDUStreamProvider) lazyLoadMembers(
-	ctx context.Context, roomID string,
+	ctx context.Context, snapshot storage.DatabaseTransaction, roomID string,
 	incremental, limited bool, stateFilter *gomatrixserverlib.StateFilter,
 	device *userapi.Device,
 	timelineEvents, stateEvents []*gomatrixserverlib.HeaderedEvent,
@@ -598,7 +567,7 @@ func (p *PDUStreamProvider) lazyLoadMembers(
 	filter.Limit = stateFilter.Limit
 	filter.Senders = &wantUsers
 	filter.Types = &[]string{gomatrixserverlib.MRoomMember}
-	memberships, err := p.DB.GetStateEventsForRoom(ctx, roomID, &filter)
+	memberships, err := snapshot.GetStateEventsForRoom(ctx, roomID, &filter)
 	if err != nil {
 		return stateEvents, err
 	}
@@ -612,8 +581,8 @@ func (p *PDUStreamProvider) lazyLoadMembers(
 
 // addIgnoredUsersToFilter adds ignored users to the eventfilter and
 // the syncreq itself for further use in streams.
-func (p *PDUStreamProvider) addIgnoredUsersToFilter(ctx context.Context, req *types.SyncRequest, eventFilter *gomatrixserverlib.RoomEventFilter) error {
+func (p *PDUStreamProvider) addIgnoredUsersToFilter(ctx context.Context, snapshot storage.DatabaseTransaction, req *types.SyncRequest, eventFilter *gomatrixserverlib.RoomEventFilter) error {
-	ignores, err := p.DB.IgnoresForUser(ctx, req.Device.UserID)
+	ignores, err := snapshot.IgnoresForUser(ctx, req.Device.UserID)
 	if err != nil {
 		if err == sql.ErrNoRows {
 			return nil

syncapi/streams/stream_presence.go

@@ -23,20 +23,26 @@ import (
 	"github.com/tidwall/gjson"
 
 	"github.com/matrix-org/dendrite/syncapi/notifier"
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
 type PresenceStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 	// cache contains previously sent presence updates to avoid unneeded updates
 	cache    sync.Map
 	notifier *notifier.Notifier
 }
 
-func (p *PresenceStreamProvider) Setup() {
+func (p *PresenceStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
-	id, err := p.DB.MaxStreamPositionForPresence(context.Background())
+	p.latestMutex.Lock()
+	defer p.latestMutex.Unlock()
+
+	id, err := snapshot.MaxStreamPositionForPresence(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -45,18 +51,20 @@ func (p *PresenceStreamProvider) Setup() {
 
 func (p *PresenceStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *PresenceStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
 	// We pull out a larger number than the filter asks for, since we're filtering out events later
-	presences, err := p.DB.PresenceAfter(ctx, from, gomatrixserverlib.EventFilter{Limit: 1000})
+	presences, err := snapshot.PresenceAfter(ctx, from, gomatrixserverlib.EventFilter{Limit: 1000})
 	if err != nil {
 		req.Log.WithError(err).Error("p.DB.PresenceAfter failed")
 		return from
@@ -84,7 +92,7 @@ func (p *PresenceStreamProvider) IncrementalSync(
 				}
 				// Bear in mind that this might return nil, but at least populating
 				// a nil means that there's a map entry so we won't repeat this call.
-				presences[roomUsers[i]], err = p.DB.GetPresence(ctx, roomUsers[i])
+				presences[roomUsers[i]], err = snapshot.GetPresence(ctx, roomUsers[i])
 				if err != nil {
 					req.Log.WithError(err).Error("unable to query presence for user")
 					return from

syncapi/streams/stream_receipt.go

@@ -4,18 +4,24 @@ import (
 	"context"
 	"encoding/json"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
 
 type ReceiptStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 }
 
-func (p *ReceiptStreamProvider) Setup() {
+func (p *ReceiptStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
-	id, err := p.DB.MaxStreamPositionForReceipts(context.Background())
+	p.latestMutex.Lock()
+	defer p.latestMutex.Unlock()
+
+	id, err := snapshot.MaxStreamPositionForReceipts(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -24,13 +30,15 @@ func (p *ReceiptStreamProvider) Setup() {
 
 func (p *ReceiptStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *ReceiptStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
@@ -41,7 +49,7 @@ func (p *ReceiptStreamProvider) IncrementalSync(
 		}
 	}
 
-	lastPos, receipts, err := p.DB.RoomReceiptsAfter(ctx, joinedRooms, from)
+	lastPos, receipts, err := snapshot.RoomReceiptsAfter(ctx, joinedRooms, from)
 	if err != nil {
 		req.Log.WithError(err).Error("p.DB.RoomReceiptsAfter failed")
 		return from

syncapi/streams/stream_sendtodevice.go

@@ -3,17 +3,23 @@ package streams
 import (
 	"context"
 
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
 type SendToDeviceStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 }
 
-func (p *SendToDeviceStreamProvider) Setup() {
+func (p *SendToDeviceStreamProvider) Setup(
-	p.StreamProvider.Setup()
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
+	p.DefaultStreamProvider.Setup(ctx, snapshot)
 
-	id, err := p.DB.MaxStreamPositionForSendToDeviceMessages(context.Background())
+	p.latestMutex.Lock()
+	defer p.latestMutex.Unlock()
+
+	id, err := snapshot.MaxStreamPositionForSendToDeviceMessages(ctx)
 	if err != nil {
 		panic(err)
 	}
@@ -22,18 +28,20 @@ func (p *SendToDeviceStreamProvider) Setup() {
 
 func (p *SendToDeviceStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *SendToDeviceStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {
 	// See if we have any new tasks to do for the send-to-device messaging.
-	lastPos, events, err := p.DB.SendToDeviceUpdatesForSync(req.Context, req.Device.UserID, req.Device.ID, from, to)
+	lastPos, events, err := snapshot.SendToDeviceUpdatesForSync(req.Context, req.Device.UserID, req.Device.ID, from, to)
 	if err != nil {
 		req.Log.WithError(err).Error("p.DB.SendToDeviceUpdatesForSync failed")
 		return from

syncapi/streams/stream_typing.go

@@ -5,24 +5,27 @@ import (
 	"encoding/json"
 
 	"github.com/matrix-org/dendrite/internal/caching"
+	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
 
 type TypingStreamProvider struct {
-	StreamProvider
+	DefaultStreamProvider
 	EDUCache *caching.EDUCache
 }
 
 func (p *TypingStreamProvider) CompleteSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 ) types.StreamPosition {
-	return p.IncrementalSync(ctx, req, 0, p.LatestPosition(ctx))
+	return p.IncrementalSync(ctx, snapshot, req, 0, p.LatestPosition(ctx))
 }
 
 func (p *TypingStreamProvider) IncrementalSync(
 	ctx context.Context,
+	snapshot storage.DatabaseTransaction,
 	req *types.SyncRequest,
 	from, to types.StreamPosition,
 ) types.StreamPosition {

syncapi/streams/streamprovider.go

@@ -0,0 +1,28 @@
+package streams
+
+import (
+	"context"
+
+	"github.com/matrix-org/dendrite/syncapi/storage"
+	"github.com/matrix-org/dendrite/syncapi/types"
+)
+
+type StreamProvider interface {
+	Setup(ctx context.Context, snapshot storage.DatabaseTransaction)
+
+	// Advance will update the latest position of the stream based on
+	// an update and will wake callers waiting on StreamNotifyAfter.
+	Advance(latest types.StreamPosition)
+
+	// CompleteSync will update the response to include all updates as needed
+	// for a complete sync. It will always return immediately.
+	CompleteSync(ctx context.Context, snapshot storage.DatabaseTransaction, req *types.SyncRequest) types.StreamPosition
+
+	// IncrementalSync will update the response to include all updates between
+	// the from and to sync positions. It will always return immediately,
+	// making no changes if the range contains no updates.
+	IncrementalSync(ctx context.Context, snapshot storage.DatabaseTransaction, req *types.SyncRequest, from, to types.StreamPosition) types.StreamPosition
+
+	// LatestPosition returns the latest stream position for this stream.
+	LatestPosition(ctx context.Context) types.StreamPosition
+}

syncapi/streams/streams.go

@@ -13,15 +13,15 @@ import (
 )
 
 type Streams struct {
-	PDUStreamProvider              types.StreamProvider
+	PDUStreamProvider              StreamProvider
-	TypingStreamProvider           types.StreamProvider
+	TypingStreamProvider           StreamProvider
-	ReceiptStreamProvider          types.StreamProvider
+	ReceiptStreamProvider          StreamProvider
-	InviteStreamProvider           types.StreamProvider
+	InviteStreamProvider           StreamProvider
-	SendToDeviceStreamProvider     types.StreamProvider
+	SendToDeviceStreamProvider     StreamProvider
-	AccountDataStreamProvider      types.StreamProvider
+	AccountDataStreamProvider      StreamProvider
-	DeviceListStreamProvider       types.StreamProvider
+	DeviceListStreamProvider       StreamProvider
-	NotificationDataStreamProvider types.StreamProvider
+	NotificationDataStreamProvider StreamProvider
-	PresenceStreamProvider         types.StreamProvider
+	PresenceStreamProvider         StreamProvider
 }
 
 func NewSyncStreamProviders(
@@ -31,51 +31,58 @@ func NewSyncStreamProviders(
 ) *Streams {
 	streams := &Streams{
 		PDUStreamProvider: &PDUStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 			lazyLoadCache:         lazyLoadCache,
 			rsAPI:                 rsAPI,
 			notifier:              notifier,
 		},
 		TypingStreamProvider: &TypingStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 			EDUCache:              eduCache,
 		},
 		ReceiptStreamProvider: &ReceiptStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 		},
 		InviteStreamProvider: &InviteStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 		},
 		SendToDeviceStreamProvider: &SendToDeviceStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 		},
 		AccountDataStreamProvider: &AccountDataStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 			userAPI:               userAPI,
 		},
 		NotificationDataStreamProvider: &NotificationDataStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 		},
 		DeviceListStreamProvider: &DeviceListStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 			rsAPI:                 rsAPI,
 			keyAPI:                keyAPI,
 		},
 		PresenceStreamProvider: &PresenceStreamProvider{
-			StreamProvider: StreamProvider{DB: d},
+			DefaultStreamProvider: DefaultStreamProvider{DB: d},
 			notifier:              notifier,
 		},
 	}
 
-	streams.PDUStreamProvider.Setup()
+	ctx := context.TODO()
-	streams.TypingStreamProvider.Setup()
+	snapshot, err := d.NewDatabaseSnapshot(ctx)
-	streams.ReceiptStreamProvider.Setup()
+	if err != nil {
-	streams.InviteStreamProvider.Setup()
+		panic(err)
-	streams.SendToDeviceStreamProvider.Setup()
+	}
-	streams.AccountDataStreamProvider.Setup()
+	defer snapshot.Rollback() // nolint:errcheck
-	streams.NotificationDataStreamProvider.Setup()
+
-	streams.DeviceListStreamProvider.Setup()
+	streams.PDUStreamProvider.Setup(ctx, snapshot)
-	streams.PresenceStreamProvider.Setup()
+	streams.TypingStreamProvider.Setup(ctx, snapshot)
+	streams.ReceiptStreamProvider.Setup(ctx, snapshot)
+	streams.InviteStreamProvider.Setup(ctx, snapshot)
+	streams.SendToDeviceStreamProvider.Setup(ctx, snapshot)
+	streams.AccountDataStreamProvider.Setup(ctx, snapshot)
+	streams.NotificationDataStreamProvider.Setup(ctx, snapshot)
+	streams.DeviceListStreamProvider.Setup(ctx, snapshot)
+	streams.PresenceStreamProvider.Setup(ctx, snapshot)
 
 	return streams
 }

syncapi/streams/template_stream.go

@@ -8,16 +8,18 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/types"
 )
 
-type StreamProvider struct {
+type DefaultStreamProvider struct {
 	DB          storage.Database
 	latest      types.StreamPosition
 	latestMutex sync.RWMutex
 }
 
-func (p *StreamProvider) Setup() {
+func (p *DefaultStreamProvider) Setup(
+	ctx context.Context, snapshot storage.DatabaseTransaction,
+) {
 }
 
-func (p *StreamProvider) Advance(
+func (p *DefaultStreamProvider) Advance(
 	latest types.StreamPosition,
 ) {
 	p.latestMutex.Lock()
@@ -28,7 +30,7 @@ func (p *StreamProvider) Advance(
 	}
 }
 
-func (p *StreamProvider) LatestPosition(
+func (p *DefaultStreamProvider) LatestPosition(
 	ctx context.Context,
 ) types.StreamPosition {
 	p.latestMutex.RLock()

syncapi/sync/requestpool.go

@@ -305,6 +305,13 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *userapi.
 			syncReq.Log.WithField("currentPos", currentPos).Debugln("Responding to sync immediately")
 		}
 
+		snapshot, err := rp.db.NewDatabaseSnapshot(req.Context())
+		if err != nil {
+			logrus.WithError(err).Error("Failed to acquire database snapshot for sync request")
+			return jsonerror.InternalServerError()
+		}
+		defer snapshot.Rollback() // nolint:errcheck
+
 		if syncReq.Since.IsEmpty() {
 			// Complete sync
 			syncReq.Response.NextBatch = types.StreamingToken{
@@ -312,70 +319,70 @@ func (rp *RequestPool) OnIncomingSyncRequest(req *http.Request, device *userapi.
 				// might advance while processing other streams, resulting in flakey
 				// tests.
 				DeviceListPosition: rp.streams.DeviceListStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				PDUPosition: rp.streams.PDUStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				TypingPosition: rp.streams.TypingStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				ReceiptPosition: rp.streams.ReceiptStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				InvitePosition: rp.streams.InviteStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				SendToDevicePosition: rp.streams.SendToDeviceStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				AccountDataPosition: rp.streams.AccountDataStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				NotificationDataPosition: rp.streams.NotificationDataStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 				PresencePosition: rp.streams.PresenceStreamProvider.CompleteSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 				),
 			}
 		} else {
 			// Incremental sync
 			syncReq.Response.NextBatch = types.StreamingToken{
 				PDUPosition: rp.streams.PDUStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.PDUPosition, currentPos.PDUPosition,
 				),
 				TypingPosition: rp.streams.TypingStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.TypingPosition, currentPos.TypingPosition,
 				),
 				ReceiptPosition: rp.streams.ReceiptStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.ReceiptPosition, currentPos.ReceiptPosition,
 				),
 				InvitePosition: rp.streams.InviteStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.InvitePosition, currentPos.InvitePosition,
 				),
 				SendToDevicePosition: rp.streams.SendToDeviceStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.SendToDevicePosition, currentPos.SendToDevicePosition,
 				),
 				AccountDataPosition: rp.streams.AccountDataStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.AccountDataPosition, currentPos.AccountDataPosition,
 				),
 				NotificationDataPosition: rp.streams.NotificationDataStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.NotificationDataPosition, currentPos.NotificationDataPosition,
 				),
 				DeviceListPosition: rp.streams.DeviceListStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.DeviceListPosition, currentPos.DeviceListPosition,
 				),
 				PresencePosition: rp.streams.PresenceStreamProvider.IncrementalSync(
-					syncReq.Context, syncReq,
+					syncReq.Context, snapshot, syncReq,
 					syncReq.Since.PresencePosition, currentPos.PresencePosition,
 				),
 			}
@@ -437,9 +444,15 @@ func (rp *RequestPool) OnIncomingKeyChangeRequest(req *http.Request, device *use
 		util.GetLogger(req.Context()).WithError(err).Error("newSyncRequest failed")
 		return jsonerror.InternalServerError()
 	}
-	rp.streams.PDUStreamProvider.IncrementalSync(req.Context(), syncReq, fromToken.PDUPosition, toToken.PDUPosition)
+	snapshot, err := rp.db.NewDatabaseSnapshot(req.Context())
+	if err != nil {
+		logrus.WithError(err).Error("Failed to acquire database snapshot for key change")
+		return jsonerror.InternalServerError()
+	}
+	defer snapshot.Rollback() // nolint:errcheck
+	rp.streams.PDUStreamProvider.IncrementalSync(req.Context(), snapshot, syncReq, fromToken.PDUPosition, toToken.PDUPosition)
 	_, _, err = internal.DeviceListCatchup(
-		req.Context(), rp.db, rp.keyAPI, rp.rsAPI, syncReq.Device.UserID,
+		req.Context(), snapshot, rp.keyAPI, rp.rsAPI, syncReq.Device.UserID,
 		syncReq.Response, fromToken.DeviceListPosition, toToken.DeviceListPosition,
 	)
 	if err != nil {

syncapi/types/provider.go

@@ -41,23 +41,3 @@ func (r *SyncRequest) IsRoomPresent(roomID string) bool {
 		return false
 	}
 }
-
-type StreamProvider interface {
-	Setup()
-
-	// Advance will update the latest position of the stream based on
-	// an update and will wake callers waiting on StreamNotifyAfter.
-	Advance(latest StreamPosition)
-
-	// CompleteSync will update the response to include all updates as needed
-	// for a complete sync. It will always return immediately.
-	CompleteSync(ctx context.Context, req *SyncRequest) StreamPosition
-
-	// IncrementalSync will update the response to include all updates between
-	// the from and to sync positions. It will always return immediately,
-	// making no changes if the range contains no updates.
-	IncrementalSync(ctx context.Context, req *SyncRequest, from, to StreamPosition) StreamPosition
-
-	// LatestPosition returns the latest stream position for this stream.
-	LatestPosition(ctx context.Context) StreamPosition
-}