etcdserver: separate maybeCompactRaftLog function to compact raft log independently

server/etcdserver/memory_storage_test.go

@@ -0,0 +1,67 @@
+// Copyright 2024 The etcd Authors
+//
+// 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 etcdserver
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.etcd.io/raft/v3"
+	"go.etcd.io/raft/v3/raftpb"
+)
+
+// TestMemoryStorageCompaction tests that after calling raftStorage.Compact(compacti)
+// without errors, the dummy entry becomes {Index: compacti} and
+// raftStorage.FirstIndex() returns (compacti+1, nil).
+func TestMemoryStorageCompaction(t *testing.T) {
+	// entries: [ {Index: 0} ]
+	raftStorage := raft.NewMemoryStorage()
+
+	firstIndex, err := raftStorage.FirstIndex()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(1), firstIndex)
+
+	// after appending, entries should be:
+	// [ {Index: 0}, {Index: 1}, {Index: 2}, {Index: 3}, {Index: 4}, {Index: 5} ]
+	appliedIndex := uint64(1)
+	for ; appliedIndex <= 5; appliedIndex++ {
+		e := raftpb.Entry{
+			Type:  raftpb.EntryNormal,
+			Term:  1,
+			Index: appliedIndex,
+		}
+		err := raftStorage.Append([]raftpb.Entry{e})
+		assert.NoError(t, err)
+	}
+
+	firstIndex, err = raftStorage.FirstIndex()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(1), firstIndex)
+
+	lastIndex, err := raftStorage.LastIndex()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(5), lastIndex)
+
+	// after compacting, entries should be:
+	// [ {Index: 3}, {Index: 4}, {Index: 5} ]
+	err = raftStorage.Compact(3)
+	assert.NoError(t, err)
+
+
+	firstIndex, err = raftStorage.FirstIndex()
+	assert.NoError(t, err)
+	assert.Equal(t, uint64(3+1), firstIndex)
+}

server/etcdserver/server.go

@@ -765,7 +765,7 @@ func (s *EtcdServer) run() {
 	if err != nil {
 		lg.Panic("failed to get snapshot from Raft storage", zap.Error(err))
 	}
-	fi, err := s.r.raftStorage.FirstIndex()
+	firstIndex, err := s.r.raftStorage.FirstIndex()
 	if err != nil {
 		lg.Panic("failed to get first index from Raft storage", zap.Error(err))
 	}
@@ -818,7 +818,13 @@ func (s *EtcdServer) run() {
 		snapi:     sn.Metadata.Index,
 		appliedt:  sn.Metadata.Term,
 		appliedi:  sn.Metadata.Index,
-		compacti:  fi - 1,
+		// compacti is the index from the last time raftStorage.Compact was called
+		// without errors.
+		//
+		// After calling raftStorage.Compact(compacti) without errors, the dummy entry of
+		// raftStorage becomes {Index: compacti}, and raftStorage.FirstIndex() returns
+		// (compacti+1, nil). This is validated by TestMemoryStorageCompaction.
+		compacti:  firstIndex - 1,
 	}
 
 	defer func() {
@@ -2205,7 +2211,6 @@ func (s *EtcdServer) maybeCompactRaftLog(ep *etcdProgress) {
 	}
 
 	err := s.r.raftStorage.Compact(compacti)
-	ep.compacti = compacti
 	if err != nil {
 		// the compaction was done asynchronously with the progress of raft.
 		// raft log might already been compact.
@@ -2214,6 +2219,7 @@ func (s *EtcdServer) maybeCompactRaftLog(ep *etcdProgress) {
 		}
 		lg.Panic("failed to compact", zap.Error(err))
 	}
+	ep.compacti = compacti
 	lg.Info(
 		"compacted Raft logs",
 		zap.Uint64("compact-index", compacti),