dendrite/federationsender/types/statistics.go

123 lines
4.0 KiB
Go

package types
import (
"math"
"sync"
"time"
"github.com/matrix-org/gomatrixserverlib"
"go.uber.org/atomic"
)
const (
// How many times should we tolerate consecutive failures before we
// just blacklist the host altogether? Bear in mind that the backoff
// is exponential, so the max time here to attempt is 2**failures.
FailuresUntilBlacklist = 16 // 16 equates to roughly 18 hours.
)
// Statistics contains information about all of the remote federated
// hosts that we have interacted with. It is basically a threadsafe
// wrapper.
type Statistics struct {
servers map[gomatrixserverlib.ServerName]*ServerStatistics
mutex sync.RWMutex
}
// 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{}
s.servers[serverName] = server
s.mutex.Unlock()
}
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 {
blacklisted atomic.Bool // is the remote side dead?
backoffUntil atomic.Value // time.Time to wait until before sending requests
failCounter atomic.Uint32 // how many times have we failed?
successCounter atomic.Uint32 // how many times have we succeeded?
}
// 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.successCounter.Add(1)
s.failCounter.Store(0)
s.blacklisted.Store(false)
}
// Failure marks a failure and works out when to backoff until. It
// returns true if the worker should give up altogether because of
// too many consecutive failures. At this point the host is marked
// as blacklisted.
func (s *ServerStatistics) Failure() bool {
// Increase the fail counter.
failCounter := s.failCounter.Add(1)
// Check that we haven't failed more times than is acceptable.
if failCounter >= FailuresUntilBlacklist {
// We've exceeded the maximum amount of times we're willing
// to back off, which is probably in the region of hours by
// now. Mark the host as blacklisted and tell the caller to
// give up.
s.blacklisted.Store(true)
return true
}
// We're still under the threshold so work out the exponential
// backoff based on how many times we have failed already. The
// worker goroutine will wait until this time before processing
// anything from the queue.
backoffSeconds := time.Second * time.Duration(math.Exp2(float64(failCounter)))
s.backoffUntil.Store(
time.Now().Add(backoffSeconds),
)
return false
}
// BackoffDuration returns both a bool stating whether to wait,
// and then if true, a duration to wait for.
func (s *ServerStatistics) BackoffDuration() (bool, time.Duration) {
backoff, until := false, time.Second
if b, ok := s.backoffUntil.Load().(time.Time); ok {
if b.After(time.Now()) {
backoff, until = true, time.Until(b)
}
}
return backoff, until
}
// Blacklisted returns true if the server is blacklisted and false
// otherwise.
func (s *ServerStatistics) Blacklisted() bool {
return s.blacklisted.Load()
}
// SuccessCount returns the number of successful requests. This is
// usually useful in constructing transaction IDs.
func (s *ServerStatistics) SuccessCount() uint32 {
return s.successCounter.Load()
}