etcdserver: keep raft log entries up to snapshot index

Signed-off-by: Clement <[email protected]>

Author: clement2026

server/config/config.go

@@ -58,6 +58,10 @@ type ServerConfig struct {
 	// follower to catch up.
 	SnapshotCatchUpEntries uint64
 
+	// CompactRaftLogEveryNApplies compact raft log once every N applies.
+	// Minimum value is 1, which means compacting raft log every apply.
+	CompactRaftLogEveryNApplies uint64
+
 	MaxSnapFiles uint
 	MaxWALFiles  uint
 

server/etcdserver/server.go

@@ -84,6 +84,10 @@ const (
 	// follower to catch up.
 	DefaultSnapshotCatchUpEntries uint64 = 5000
 
+	// DefaultCompactRaftLogEveryNApplies compact raft log once every N applies.
+	// Minimum value is 1, which means compacting raft log every apply.
+	DefaultCompactRaftLogEveryNApplies uint64 = 10
+
 	StoreClusterPrefix = "/0"
 	StoreKeysPrefix    = "/1"
 
@@ -569,6 +573,14 @@ func (s *EtcdServer) start() {
 		)
 		s.Cfg.SnapshotCatchUpEntries = DefaultSnapshotCatchUpEntries
 	}
+	if s.Cfg.CompactRaftLogEveryNApplies == 0 {
+		lg.Info(
+			"updating compact raft log every N applies to default",
+			zap.Uint64("given-compact-raft-log-every-n-applies", s.Cfg.CompactRaftLogEveryNApplies),
+			zap.Uint64("updated-compact-raft-log-every-n-applies", DefaultCompactRaftLogEveryNApplies),
+		)
+		s.Cfg.CompactRaftLogEveryNApplies = DefaultCompactRaftLogEveryNApplies
+	}
 
 	s.w = wait.New()
 	s.applyWait = wait.NewTimeList()
@@ -980,6 +992,7 @@ func (s *EtcdServer) applyAll(ep *etcdProgress, apply *toApply) {
 	<-apply.notifyc
 
 	s.triggerSnapshot(ep)
+	s.maybeCompactRaftLog(ep)
 	select {
 	// snapshot requested via send()
 	case m := <-s.r.msgSnapC:
@@ -2170,6 +2183,18 @@ func (s *EtcdServer) snapshot(snapi uint64, confState raftpb.ConfState) {
 		"saved snapshot",
 		zap.Uint64("snapshot-index", snap.Metadata.Index),
 	)
+}
+
+func (s *EtcdServer) maybeCompactRaftLog(ep *etcdProgress) {
+	lg := s.Logger()
+
+	// Keep some in memory log entries for slow followers, while keeping the entries up to snapshot index.
+	// Only compact raft log once every N applies
+	if ep.appliedi <= ep.snapi+s.Cfg.SnapshotCatchUpEntries || ep.appliedi%s.Cfg.CompactRaftLogEveryNApplies != 0 {
+		return
+	}
+
+	compacti := ep.appliedi - s.Cfg.SnapshotCatchUpEntries
 
 	// When sending a snapshot, etcd will pause compaction.
 	// After receives a snapshot, the slow follower needs to get all the entries right after
@@ -2181,13 +2206,7 @@ func (s *EtcdServer) snapshot(snapi uint64, confState raftpb.ConfState) {
 		return
 	}
 
-	// keep some in memory log entries for slow followers.
-	compacti := uint64(1)
-	if snapi > s.Cfg.SnapshotCatchUpEntries {
-		compacti = snapi - s.Cfg.SnapshotCatchUpEntries
-	}
-
-	err = s.r.raftStorage.Compact(compacti)
+	err := s.r.raftStorage.Compact(compacti)
 	if err != nil {
 		// the compaction was done asynchronously with the progress of raft.
 		// raft log might already been compact.

tests/framework/integration/cluster.go

@@ -148,8 +148,9 @@ type ClusterConfig struct {
 	MaxTxnOps       uint
 	MaxRequestBytes uint
 
-	SnapshotCount          uint64
-	SnapshotCatchUpEntries uint64
+	SnapshotCount               uint64
+	SnapshotCatchUpEntries      uint64
+	CompactRaftLogEveryNApplies uint64
 
 	GRPCKeepAliveMinTime        time.Duration
 	GRPCKeepAliveInterval       time.Duration
@@ -276,6 +277,7 @@ func (c *Cluster) mustNewMember(t testutil.TB) *Member {
 			MaxRequestBytes:             c.Cfg.MaxRequestBytes,
 			SnapshotCount:               c.Cfg.SnapshotCount,
 			SnapshotCatchUpEntries:      c.Cfg.SnapshotCatchUpEntries,
+			CompactRaftLogEveryNApplies: c.Cfg.CompactRaftLogEveryNApplies,
 			GRPCKeepAliveMinTime:        c.Cfg.GRPCKeepAliveMinTime,
 			GRPCKeepAliveInterval:       c.Cfg.GRPCKeepAliveInterval,
 			GRPCKeepAliveTimeout:        c.Cfg.GRPCKeepAliveTimeout,
@@ -601,6 +603,7 @@ type MemberConfig struct {
 	MaxRequestBytes             uint
 	SnapshotCount               uint64
 	SnapshotCatchUpEntries      uint64
+	CompactRaftLogEveryNApplies uint64
 	GRPCKeepAliveMinTime        time.Duration
 	GRPCKeepAliveInterval       time.Duration
 	GRPCKeepAliveTimeout        time.Duration
@@ -686,6 +689,10 @@ func MustNewMember(t testutil.TB, mcfg MemberConfig) *Member {
 	if mcfg.SnapshotCatchUpEntries != 0 {
 		m.SnapshotCatchUpEntries = mcfg.SnapshotCatchUpEntries
 	}
+	m.CompactRaftLogEveryNApplies = etcdserver.DefaultCompactRaftLogEveryNApplies
+	if mcfg.CompactRaftLogEveryNApplies != 0 {
+		m.CompactRaftLogEveryNApplies = mcfg.CompactRaftLogEveryNApplies
+	}
 
 	// for the purpose of integration testing, simple token is enough
 	m.AuthToken = "simple"

tests/integration/v3_watch_restore_test.go

@@ -55,9 +55,10 @@ func TestV3WatchRestoreSnapshotUnsync(t *testing.T) {
 	integration.BeforeTest(t)
 
 	clus := integration.NewCluster(t, &integration.ClusterConfig{
-		Size:                   3,
-		SnapshotCount:          10,
-		SnapshotCatchUpEntries: 5,
+		Size:                        3,
+		SnapshotCount:               10,
+		SnapshotCatchUpEntries:      5,
+		CompactRaftLogEveryNApplies: 10,
 	})
 	defer clus.Terminate(t)
 
@@ -102,11 +103,12 @@ func TestV3WatchRestoreSnapshotUnsync(t *testing.T) {
 	// elected. Leader will apply 3 MemberAttrSet and 1 ClusterVersionSet
 	// changes. So member 0 has index 8 in raft log before network
 	// partition. We need to trigger EtcdServer.snapshot() at least twice.
+	// Raft log is only compacted when appliedi%CompactRaftLogEveryNApplies==0
 	//
-	// SnapshotCount: 10, SnapshotCatchUpEntries: 5
+	// SnapshotCount: 10, SnapshotCatchUpEntries: 5, CompactRaftLogEveryNApplies: 10
 	//
-	// T1: L(snapshot-index: 11, compacted-index:  6), F_m0(index:8)
-	// T2: L(snapshot-index: 22, compacted-index: 17), F_m0(index:8, out of date)
+	// T1: L(snapshot-index: 11, compacted-index:  5), F_m0(index:8)
+	// T2: L(snapshot-index: 22, compacted-index: 15), F_m0(index:8, out of date)
 	//
 	// Since there is no way to confirm server has compacted the log, we
 	// use log monitor to watch and expect "compacted Raft logs" content.