[3.5] fix revision loss issue caused by compaction - 17780

server/mvcc/kvstore.go

@@ -380,6 +380,17 @@ func (s *store) restore() error {
 		if s.currentRev < s.compactMainRev {
 			s.currentRev = s.compactMainRev
 		}
+
+		// If the latest revision was a tombstone revision and etcd just compacted
+		// it, but crashed right before persisting the FinishedCompactRevision,
+		// then it would lead to revision decreasing in bbolt db file. In such
+		// a scenario, we should adjust the current revision using the scheduled
+		// compact revision on bootstrap when etcd gets started again.
+		//
+		// See https://github.com/etcd-io/etcd/issues/17780#issuecomment-2061900231
+		if s.currentRev < scheduledCompact {
+			s.currentRev = scheduledCompact
+		}
 		s.revMu.Unlock()
 	}
 

server/mvcc/kvstore_compaction.go

@@ -59,6 +59,7 @@ func (s *store) scheduleCompaction(compactMainRev, prevCompactRev int64) (KeyVal
 		}
 
 		if len(keys) < s.cfg.CompactionBatchLimit {
+			// gofail: var compactBeforeSetFinishedCompact struct{}
 			rbytes := make([]byte, 8+1+8)
 			revToBytes(revision{main: compactMainRev}, rbytes)
 			tx.UnsafePut(buckets.Meta, finishedCompactKeyName, rbytes)

tests/e2e/reproduce_17780_test.go

@@ -0,0 +1,115 @@
+// 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 e2e
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	clientv3 "go.etcd.io/etcd/client/v3"
+	"go.etcd.io/etcd/pkg/v3/stringutil"
+	"go.etcd.io/etcd/tests/v3/framework/e2e"
+)
+
+// TestReproduce17780 reproduces the issue: https://github.com/etcd-io/etcd/issues/17780.
+func TestReproduce17780(t *testing.T) {
+	e2e.BeforeTest(t)
+
+	compactionBatchLimit := 10
+
+	ctx := context.TODO()
+	clus, cerr := e2e.NewEtcdProcessCluster(t,
+		&e2e.EtcdProcessClusterConfig{
+			ClusterSize:                3,
+			GoFailEnabled:              true,
+			SnapshotCount:              1000,
+			CompactionBatchLimit:       compactionBatchLimit,
+			WatchProcessNotifyInterval: 100 * time.Millisecond,
+		},
+	)
+	require.NoError(t, cerr)
+
+	t.Cleanup(func() { require.NoError(t, clus.Stop()) })
+
+	leaderIdx := clus.WaitLeader(t)
+	targetIdx := (leaderIdx + 1) % clus.Cfg.ClusterSize
+
+	cli := newClient(t, clus.Procs[targetIdx].EndpointsGRPC(), e2e.ClientNonTLS, false)
+
+	// Revision: 2 -> 8 for new keys
+	n := compactionBatchLimit - 2
+	valueSize := 16
+	for i := 2; i <= n; i++ {
+		_, err := cli.Put(ctx, fmt.Sprintf("%d", i), stringutil.RandString(uint(valueSize)))
+		require.NoError(t, err)
+	}
+
+	// Revision: 9 -> 11 for delete keys with compared revision
+	//
+	// We need last compaction batch is no-op and all the tombstones should
+	// be deleted in previous compaction batch. So that we just lost the
+	// finishedCompactRev after panic.
+	for i := 9; i <= compactionBatchLimit+1; i++ {
+		rev := i - 5
+		key := fmt.Sprintf("%d", rev)
+
+		_, err := cli.Delete(ctx, key)
+		require.NoError(t, err)
+	}
+
+	require.NoError(t, clus.Procs[targetIdx].Failpoints().SetupHTTP(ctx, "compactBeforeSetFinishedCompact", `panic`))
+
+	_, err := cli.Compact(ctx, 11, clientv3.WithCompactPhysical())
+	require.Error(t, err)
+
+	require.Error(t, clus.Procs[targetIdx].Stop())
+	// NOTE: The proc panics and exit code is 2. It's impossible to restart
+	// that etcd proc because last exit code is 2 and Restart() refuses to
+	// start new one. Using IsRunning() function is to cleanup status.
+	require.False(t, clus.Procs[targetIdx].IsRunning())
+	require.NoError(t, clus.Procs[targetIdx].Restart())
+
+	// NOTE: We should not decrease the revision if there is no record
+	// about finished compact operation.
+	resp, err := cli.Get(ctx, fmt.Sprintf("%d", n))
+	require.NoError(t, err)
+	assert.GreaterOrEqual(t, resp.Header.Revision, int64(11))
+
+	// Revision 4 should be deleted by compaction.
+	resp, err = cli.Get(ctx, fmt.Sprintf("%d", 4))
+	require.NoError(t, err)
+	require.True(t, resp.Count == 0)
+
+	next := 20
+	for i := 12; i <= next; i++ {
+		_, err := cli.Put(ctx, fmt.Sprintf("%d", i), stringutil.RandString(uint(valueSize)))
+		require.NoError(t, err)
+	}
+
+	expectedRevision := next
+	for procIdx, proc := range clus.Procs {
+		cli = newClient(t, proc.EndpointsGRPC(), e2e.ClientNonTLS, false)
+		resp, err := cli.Get(ctx, fmt.Sprintf("%d", next))
+		require.NoError(t, err)
+
+		assert.GreaterOrEqual(t, resp.Header.Revision, int64(expectedRevision),
+			fmt.Sprintf("LeaderIdx: %d, Current: %d", leaderIdx, procIdx))
+	}
+}