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[release-3.5] backport fix watch event loss after compaction #17612

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5 changes: 5 additions & 0 deletions server/mvcc/watchable_store.go
Original file line number Diff line number Diff line change
Expand Up @@ -366,6 +366,11 @@ func (s *watchableStore) syncWatchers() int {
var victims watcherBatch
wb := newWatcherBatch(wg, evs)
for w := range wg.watchers {
if w.minRev < compactionRev {
// Skip the watcher that failed to send compacted watch response due to w.ch is full.
// Next retry of syncWatchers would try to resend the compacted watch response to w.ch
continue
}
w.minRev = curRev + 1

eb, ok := wb[w]
Expand Down
61 changes: 60 additions & 1 deletion server/mvcc/watchable_store_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -23,11 +23,14 @@ import (
"testing"
"time"

"github.com/stretchr/testify/require"
"go.uber.org/zap"
"go.uber.org/zap/zaptest"

"go.etcd.io/etcd/api/v3/mvccpb"
"go.etcd.io/etcd/pkg/v3/traceutil"
"go.etcd.io/etcd/server/v3/lease"
betesting "go.etcd.io/etcd/server/v3/mvcc/backend/testing"
"go.uber.org/zap"
)

func TestWatch(t *testing.T) {
Expand Down Expand Up @@ -259,6 +262,62 @@ func TestWatchCompacted(t *testing.T) {
}
}

func TestWatchNoEventLossOnCompact(t *testing.T) {
oldChanBufLen, oldMaxWatchersPerSync := chanBufLen, maxWatchersPerSync
b, tmpPath := betesting.NewDefaultTmpBackend(t)
lg := zaptest.NewLogger(t)
s := newWatchableStore(lg, b, &lease.FakeLessor{}, StoreConfig{})

defer func() {
cleanup(s, b, tmpPath)
chanBufLen, maxWatchersPerSync = oldChanBufLen, oldMaxWatchersPerSync
}()

chanBufLen, maxWatchersPerSync = 1, 4
testKey, testValue := []byte("foo"), []byte("bar")

maxRev := 10
compactRev := int64(5)
for i := 0; i < maxRev; i++ {
s.Put(testKey, testValue, lease.NoLease)
}
_, err := s.Compact(traceutil.TODO(), compactRev)
require.NoErrorf(t, err, "failed to compact kv (%v)", err)

w := s.NewWatchStream()
defer w.Close()

watchers := map[WatchID]int64{
0: 1,
1: 1, // create unsyncd watchers with startRev < compactRev
2: 6, // create unsyncd watchers with compactRev < startRev < currentRev
}
for id, startRev := range watchers {
_, err := w.Watch(id, testKey, nil, startRev)
require.NoError(t, err)
}
// fill up w.Chan() with 1 buf via 2 compacted watch response
s.syncWatchers()

for len(watchers) > 0 {
resp := <-w.Chan()
if resp.CompactRevision != 0 {
require.Equal(t, resp.CompactRevision, compactRev)
require.Contains(t, watchers, resp.WatchID)
delete(watchers, resp.WatchID)
continue
}
nextRev := watchers[resp.WatchID]
for _, ev := range resp.Events {
require.Equalf(t, nextRev, ev.Kv.ModRevision, "got event revision %d but want %d for watcher with watch ID %d", ev.Kv.ModRevision, nextRev, resp.WatchID)
nextRev++
}
if nextRev == s.rev()+1 {
delete(watchers, resp.WatchID)
}
}
}

func TestWatchFutureRev(t *testing.T) {
b, tmpPath := betesting.NewDefaultTmpBackend(t)
s := newWatchableStore(zap.NewExample(), b, &lease.FakeLessor{}, StoreConfig{})
Expand Down