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dendrite/federationapi/statistics/statistics.go
devonh 241d5c47df
Refactor Federation Destination Queues (#2807)
This is a refactor of the federation destination queues.
It fixes a few things, namely:
- actually retry outgoing events with backoff behaviour
- obtain enough events from the database to fill messages as much as
possible
- minimize the amount of running goroutines
  - use pure timers for backoff
  - don't restart queue unless necessary
  - close the background task when backing off
- increase max edus in a transaction to match the spec
- cleanup timers more aggresively to reduce memory usage
- add jitter to backoff timers to reduce resource spikes
- add a bunch of tests (with real and fake databases) to ensure
everything is working
2022-10-19 11:03:16 +01:00

224 lines
7.5 KiB
Go

package statistics
import (
"math"
"math/rand"
"sync"
"time"
"github.com/matrix-org/gomatrixserverlib"
"github.com/sirupsen/logrus"
"go.uber.org/atomic"
"github.com/matrix-org/dendrite/federationapi/storage"
)
// Statistics contains information about all of the remote federated
// hosts that we have interacted with. It is basically a threadsafe
// wrapper.
type Statistics struct {
DB storage.Database
servers map[gomatrixserverlib.ServerName]*ServerStatistics
mutex sync.RWMutex
backoffTimers map[gomatrixserverlib.ServerName]*time.Timer
backoffMutex sync.RWMutex
// How many times should we tolerate consecutive failures before we
// just blacklist the host altogether? The backoff is exponential,
// so the max time here to attempt is 2**failures seconds.
FailuresUntilBlacklist uint32
}
func NewStatistics(db storage.Database, failuresUntilBlacklist uint32) Statistics {
return Statistics{
DB: db,
FailuresUntilBlacklist: failuresUntilBlacklist,
backoffTimers: make(map[gomatrixserverlib.ServerName]*time.Timer),
}
}
// ForServer returns server statistics for the given server name. If it
// does not exist, it will create empty statistics and return those.
func (s *Statistics) ForServer(serverName gomatrixserverlib.ServerName) *ServerStatistics {
// If the map hasn't been initialised yet then do that.
if s.servers == nil {
s.mutex.Lock()
s.servers = make(map[gomatrixserverlib.ServerName]*ServerStatistics)
s.mutex.Unlock()
}
// Look up if we have statistics for this server already.
s.mutex.RLock()
server, found := s.servers[serverName]
s.mutex.RUnlock()
// If we don't, then make one.
if !found {
s.mutex.Lock()
server = &ServerStatistics{
statistics: s,
serverName: serverName,
}
s.servers[serverName] = server
s.mutex.Unlock()
blacklisted, err := s.DB.IsServerBlacklisted(serverName)
if err != nil {
logrus.WithError(err).Errorf("Failed to get blacklist entry %q", serverName)
} else {
server.blacklisted.Store(blacklisted)
}
}
return server
}
// ServerStatistics contains information about our interactions with a
// remote federated host, e.g. how many times we were successful, how
// many times we failed etc. It also manages the backoff time and black-
// listing a remote host if it remains uncooperative.
type ServerStatistics struct {
statistics *Statistics //
serverName gomatrixserverlib.ServerName //
blacklisted atomic.Bool // is the node blacklisted
backoffStarted atomic.Bool // is the backoff started
backoffUntil atomic.Value // time.Time until this backoff interval ends
backoffCount atomic.Uint32 // number of times BackoffDuration has been called
successCounter atomic.Uint32 // how many times have we succeeded?
backoffNotifier func() // notifies destination queue when backoff completes
notifierMutex sync.Mutex
}
const maxJitterMultiplier = 1.4
const minJitterMultiplier = 0.8
// duration returns how long the next backoff interval should be.
func (s *ServerStatistics) duration(count uint32) time.Duration {
// Add some jitter to minimise the chance of having multiple backoffs
// ending at the same time.
jitter := rand.Float64()*(maxJitterMultiplier-minJitterMultiplier) + minJitterMultiplier
duration := time.Millisecond * time.Duration(math.Exp2(float64(count))*jitter*1000)
return duration
}
// cancel will interrupt the currently active backoff.
func (s *ServerStatistics) cancel() {
s.blacklisted.Store(false)
s.backoffUntil.Store(time.Time{})
s.ClearBackoff()
}
// AssignBackoffNotifier configures the channel to send to when
// a backoff completes.
func (s *ServerStatistics) AssignBackoffNotifier(notifier func()) {
s.notifierMutex.Lock()
defer s.notifierMutex.Unlock()
s.backoffNotifier = notifier
}
// Success updates the server statistics with a new successful
// attempt, which increases the sent counter and resets the idle and
// failure counters. If a host was blacklisted at this point then
// we will unblacklist it.
func (s *ServerStatistics) Success() {
s.cancel()
s.backoffCount.Store(0)
s.successCounter.Inc()
if s.statistics.DB != nil {
if err := s.statistics.DB.RemoveServerFromBlacklist(s.serverName); err != nil {
logrus.WithError(err).Errorf("Failed to remove %q from blacklist", s.serverName)
}
}
}
// Failure marks a failure and starts backing off if needed.
// It will return the time that the current failure
// will result in backoff waiting until, and a bool signalling
// whether we have blacklisted and therefore to give up.
func (s *ServerStatistics) Failure() (time.Time, bool) {
// Return immediately if we have blacklisted this node.
if s.blacklisted.Load() {
return time.Time{}, true
}
// If we aren't already backing off, this call will start
// a new backoff period, increase the failure counter and
// start a goroutine which will wait out the backoff and
// unset the backoffStarted flag when done.
if s.backoffStarted.CompareAndSwap(false, true) {
if s.backoffCount.Inc() >= s.statistics.FailuresUntilBlacklist {
s.blacklisted.Store(true)
if s.statistics.DB != nil {
if err := s.statistics.DB.AddServerToBlacklist(s.serverName); err != nil {
logrus.WithError(err).Errorf("Failed to add %q to blacklist", s.serverName)
}
}
s.ClearBackoff()
return time.Time{}, true
}
// We're starting a new back off so work out what the next interval
// will be.
count := s.backoffCount.Load()
until := time.Now().Add(s.duration(count))
s.backoffUntil.Store(until)
s.statistics.backoffMutex.Lock()
defer s.statistics.backoffMutex.Unlock()
s.statistics.backoffTimers[s.serverName] = time.AfterFunc(time.Until(until), s.backoffFinished)
}
return s.backoffUntil.Load().(time.Time), false
}
// ClearBackoff stops the backoff timer for this destination if it is running
// and removes the timer from the backoffTimers map.
func (s *ServerStatistics) ClearBackoff() {
// If the timer is still running then stop it so it's memory is cleaned up sooner.
s.statistics.backoffMutex.Lock()
defer s.statistics.backoffMutex.Unlock()
if timer, ok := s.statistics.backoffTimers[s.serverName]; ok {
timer.Stop()
}
delete(s.statistics.backoffTimers, s.serverName)
s.backoffStarted.Store(false)
}
// backoffFinished will clear the previous backoff and notify the destination queue.
func (s *ServerStatistics) backoffFinished() {
s.ClearBackoff()
// Notify the destinationQueue if one is currently running.
s.notifierMutex.Lock()
defer s.notifierMutex.Unlock()
if s.backoffNotifier != nil {
s.backoffNotifier()
}
}
// BackoffInfo returns information about the current or previous backoff.
// Returns the last backoffUntil time and whether the server is currently blacklisted or not.
func (s *ServerStatistics) BackoffInfo() (*time.Time, bool) {
until, ok := s.backoffUntil.Load().(time.Time)
if ok {
return &until, s.blacklisted.Load()
}
return nil, s.blacklisted.Load()
}
// Blacklisted returns true if the server is blacklisted and false
// otherwise.
func (s *ServerStatistics) Blacklisted() bool {
return s.blacklisted.Load()
}
// RemoveBlacklist removes the blacklisted status from the server.
func (s *ServerStatistics) RemoveBlacklist() {
s.cancel()
s.backoffCount.Store(0)
}
// SuccessCount returns the number of successful requests. This is
// usually useful in constructing transaction IDs.
func (s *ServerStatistics) SuccessCount() uint32 {
return s.successCounter.Load()
}