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Backoff fixes (#1250)
* Backoff fixes * Update comments * Fix destination queue * Log why we're blacklisting * Fix logic fail * Logging level * Fix bug * Maybe fix that bug after all * Fix debug output * Fix tests
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@ -262,15 +262,13 @@ func (oq *destinationQueue) backgroundSend() {
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// If we are backing off this server then wait for the
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// backoff duration to complete first, or until explicitly
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// told to retry.
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if backoff, duration := oq.statistics.BackoffDuration(); backoff {
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log.WithField("duration", duration).Debugf("Backing off %s", oq.destination)
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oq.backingOff.Store(true)
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select {
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case <-time.After(duration):
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case <-oq.interruptBackoff:
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log.Debugf("Interrupting backoff for %q", oq.destination)
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}
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oq.backingOff.Store(false)
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if _, giveUp := oq.statistics.BackoffIfRequired(oq.backingOff, oq.interruptBackoff); giveUp {
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// It's been suggested that we should give up because the backoff
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// has exceeded a maximum allowable value. Clean up the in-memory
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// buffers at this point. The PDU clean-up is already on a defer.
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oq.cleanPendingInvites()
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log.Warnf("Blacklisting %q due to exceeding backoff threshold", oq.destination)
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return
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}
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// If we have pending PDUs or EDUs then construct a transaction.
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@ -278,24 +276,8 @@ func (oq *destinationQueue) backgroundSend() {
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// Try sending the next transaction and see what happens.
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transaction, terr := oq.nextTransaction()
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if terr != nil {
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// We failed to send the transaction.
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if giveUp := oq.statistics.Failure(); giveUp {
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// It's been suggested that we should give up because the backoff
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// has exceeded a maximum allowable value. Clean up the in-memory
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// buffers at this point. The PDU clean-up is already on a defer.
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oq.cleanPendingInvites()
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log.Infof("Blacklisting %q due to errors", oq.destination)
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return
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} else {
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// We haven't been told to give up terminally yet but we still have
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// PDUs waiting to be sent. By sending a message into the wake chan,
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// the next loop iteration will try processing these PDUs again,
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// subject to the backoff.
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select {
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case oq.notifyPDUs <- true:
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default:
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}
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}
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// We failed to send the transaction. Mark it as a failure.
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oq.statistics.Failure()
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} else if transaction {
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// If we successfully sent the transaction then clear out
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// the pending events and EDUs, and wipe our transaction ID.
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@ -307,14 +289,8 @@ func (oq *destinationQueue) backgroundSend() {
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if len(oq.pendingInvites) > 0 {
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sent, ierr := oq.nextInvites(oq.pendingInvites)
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if ierr != nil {
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// We failed to send the transaction so increase the
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// backoff and give it another go shortly.
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if giveUp := oq.statistics.Failure(); giveUp {
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// It's been suggested that we should give up because
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// the backoff has exceeded a maximum allowable value.
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log.Infof("Blacklisting %q due to errors", oq.destination)
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return
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}
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// We failed to send the transaction. Mark it as a failure.
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oq.statistics.Failure()
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} else if sent > 0 {
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// If we successfully sent the invites then clear out
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// the pending invites.
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@ -65,8 +65,8 @@ type ServerStatistics struct {
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statistics *Statistics //
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serverName gomatrixserverlib.ServerName //
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blacklisted atomic.Bool // is the node blacklisted
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backoffUntil atomic.Value // time.Time to wait until before sending requests
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failCounter atomic.Uint32 // how many times have we failed?
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backoffStarted atomic.Bool // is the backoff started
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backoffCount atomic.Uint32 // number of times BackoffDuration has been called
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successCounter atomic.Uint32 // how many times have we succeeded?
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}
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@ -76,55 +76,67 @@ type ServerStatistics struct {
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// we will unblacklist it.
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func (s *ServerStatistics) Success() {
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s.successCounter.Add(1)
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s.failCounter.Store(0)
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s.backoffStarted.Store(false)
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s.backoffCount.Store(0)
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s.blacklisted.Store(false)
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if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil {
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logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName)
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if s.statistics.DB != nil {
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if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil {
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logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName)
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}
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}
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}
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// Failure marks a failure and works out when to backoff until. It
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// returns true if the worker should give up altogether because of
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// too many consecutive failures. At this point the host is marked
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// as blacklisted.
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func (s *ServerStatistics) Failure() bool {
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// Increase the fail counter.
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failCounter := s.failCounter.Add(1)
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// Failure marks a failure and starts backing off if needed.
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// The next call to BackoffIfRequired will do the right thing
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// after this.
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func (s *ServerStatistics) Failure() {
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if s.backoffStarted.CAS(false, true) {
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s.backoffCount.Store(0)
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}
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}
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// Check that we haven't failed more times than is acceptable.
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if failCounter >= s.statistics.FailuresUntilBlacklist {
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// BackoffIfRequired will block for as long as the current
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// backoff requires, if needed. Otherwise it will do nothing.
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func (s *ServerStatistics) BackoffIfRequired(backingOff atomic.Bool, interrupt <-chan bool) (time.Duration, bool) {
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if started := s.backoffStarted.Load(); !started {
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return 0, false
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}
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// Work out how many times we've backed off so far.
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count := s.backoffCount.Inc()
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duration := time.Second * time.Duration(math.Exp2(float64(count)))
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// Work out if we should be blacklisting at this point.
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if count >= s.statistics.FailuresUntilBlacklist {
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// We've exceeded the maximum amount of times we're willing
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// to back off, which is probably in the region of hours by
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// now. Mark the host as blacklisted and tell the caller to
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// give up.
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s.blacklisted.Store(true)
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if err := s.statistics.DB.AddServerToBlacklist(s.serverName); err != nil {
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logrus.WithError(err).Errorf("Failed to add %q to blacklist", s.serverName)
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if s.statistics.DB != nil {
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if err := s.statistics.DB.AddServerToBlacklist(s.serverName); err != nil {
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logrus.WithError(err).Errorf("Failed to add %q to blacklist", s.serverName)
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}
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}
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return true
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return duration, true
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}
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// We're still under the threshold so work out the exponential
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// backoff based on how many times we have failed already. The
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// worker goroutine will wait until this time before processing
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// anything from the queue.
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backoffSeconds := time.Second * time.Duration(math.Exp2(float64(failCounter)))
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s.backoffUntil.Store(
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time.Now().Add(backoffSeconds),
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)
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return false
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}
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// Notify the destination queue that we're backing off now.
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backingOff.Store(true)
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defer backingOff.Store(false)
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// BackoffDuration returns both a bool stating whether to wait,
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// and then if true, a duration to wait for.
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func (s *ServerStatistics) BackoffDuration() (bool, time.Duration) {
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backoff, until := false, time.Second
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if b, ok := s.backoffUntil.Load().(time.Time); ok {
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if b.After(time.Now()) {
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backoff, until = true, time.Until(b)
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}
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// Work out how long we should be backing off for.
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logrus.Warnf("Backing off %q for %s", s.serverName, duration)
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// Wait for either an interruption or for the backoff to
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// complete.
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select {
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case <-interrupt:
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logrus.Debugf("Interrupting backoff for %q", s.serverName)
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case <-time.After(duration):
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}
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return backoff, until
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return duration, false
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}
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// Blacklisted returns true if the server is blacklisted and false
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60
federationsender/statistics/statistics_test.go
Normal file
60
federationsender/statistics/statistics_test.go
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@ -0,0 +1,60 @@
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package statistics
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import (
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"math"
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"testing"
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"time"
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"go.uber.org/atomic"
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)
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func TestBackoff(t *testing.T) {
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stats := Statistics{
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FailuresUntilBlacklist: 5,
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}
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server := ServerStatistics{
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statistics: &stats,
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serverName: "test.com",
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}
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// Start by checking that counting successes works.
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server.Success()
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if successes := server.SuccessCount(); successes != 1 {
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t.Fatalf("Expected success count 1, got %d", successes)
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}
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// Register a failure.
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server.Failure()
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t.Logf("Backoff counter: %d", server.backoffCount.Load())
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backingOff := atomic.Bool{}
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// Now we're going to simulate backing off a few times to see
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// what happens.
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for i := uint32(1); i <= 10; i++ {
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// Interrupt the backoff - it doesn't really matter if it
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// completes but we will find out how long the backoff should
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// have been.
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interrupt := make(chan bool, 1)
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close(interrupt)
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// Get the duration.
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duration, blacklist := server.BackoffIfRequired(backingOff, interrupt)
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// Check if we should be blacklisted by now.
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if i > stats.FailuresUntilBlacklist {
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if !blacklist {
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t.Fatalf("Backoff %d should have resulted in blacklist but didn't", i)
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} else {
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t.Logf("Backoff %d is blacklisted as expected", i)
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continue
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}
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}
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// Check if the duration is what we expect.
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t.Logf("Backoff %d is for %s", i, duration)
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if wanted := time.Second * time.Duration(math.Exp2(float64(i))); !blacklist && duration != wanted {
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t.Fatalf("Backoff %d should have been %s but was %s", i, wanted, duration)
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}
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}
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}
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