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eventstore: fix checkpoint update race #4987

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181555f
eventstore: fix potential race
lidezhu May 3, 2026
aa4f202
fix
lidezhu May 5, 2026
926bb42
f
lidezhu May 5, 2026
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100 changes: 50 additions & 50 deletions logservice/eventstore/event_store.go
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Original file line number Diff line number Diff line change
Expand Up @@ -115,7 +115,7 @@ type dispatcherStat struct {

resolvedTs atomic.Uint64
// the max ts of events which is not needed by this dispatcher
checkpointTs uint64
checkpointTs atomic.Uint64
// the difference between `subStat`, `pendingSubStat` and `removingSubStat`:
// 1) if there is no existing subscriptions which can be reused,
// or there is a existing subscription with exact span match,
Expand Down Expand Up @@ -498,8 +498,8 @@ func (e *eventStore) RegisterDispatcher(
stat := &dispatcherStat{
dispatcherID: dispatcherID,
tableSpan: dispatcherSpan,
checkpointTs: startTs,
}
stat.checkpointTs.Store(startTs)
stat.resolvedTs.Store(startTs)

wrappedNotifier := func(resolvedTs uint64, latestCommitTs uint64) {
Expand Down Expand Up @@ -710,7 +710,7 @@ func (e *eventStore) UpdateDispatcherCheckpointTs(
if !ok {
return
}
dispatcherStat.checkpointTs = checkpointTs
dispatcherStat.checkpointTs.Store(checkpointTs)
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@gemini-code-assist gemini-code-assist Bot May 3, 2026

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medium

To ensure that the dispatcher's checkpoint timestamp only moves forward and to handle potential concurrent updates safely, it is better to use util.CompareAndMonotonicIncrease instead of a direct Store. This prevents a stale update from regressing the checkpoint, which could incorrectly affect the minimum checkpoint calculation for the shared subscription.

Suggested change
dispatcherStat.checkpointTs.Store(checkpointTs)
util.CompareAndMonotonicIncrease(&dispatcherStat.checkpointTs, checkpointTs)


updateSubStatCheckpoint := func(subStat *subscriptionStat) {
if subStat == nil {
Expand All @@ -730,8 +730,9 @@ func (e *eventStore) UpdateDispatcherCheckpointTs(
continue
}

if newCheckpointTs == 0 || dispatcherStat.checkpointTs < newCheckpointTs {
newCheckpointTs = dispatcherStat.checkpointTs
dispatcherCheckpointTs := dispatcherStat.checkpointTs.Load()
if newCheckpointTs == 0 || dispatcherCheckpointTs < newCheckpointTs {
newCheckpointTs = dispatcherCheckpointTs
}
}

Expand All @@ -744,44 +745,39 @@ func (e *eventStore) UpdateDispatcherCheckpointTs(
if newCheckpointTs == 0 {
return
}
oldCheckpointTs := subStat.checkpointTs.Load()
if newCheckpointTs == oldCheckpointTs {
return
}
if newCheckpointTs < oldCheckpointTs {
log.Panic("should not happen",
zap.Uint64("newCheckpointTs", newCheckpointTs),
zap.Uint64("oldCheckpointTs", oldCheckpointTs))
}
// If there is no dml event after old checkpoint ts, then there is no data to be deleted.
// So we can skip adding gc item.
lastReceiveDMLTime := subStat.lastReceiveDMLTime.Load()
if lastReceiveDMLTime > 0 {
oldCheckpointPhysicalTime := oracle.GetTimeFromTS(oldCheckpointTs)
if lastReceiveDMLTime >= oldCheckpointPhysicalTime.UnixMilli() {
e.gcManager.addGCItem(
subStat.dbIndex,
uint64(subStat.subID),
subStat.tableSpan.TableID,
oldCheckpointTs,
newCheckpointTs,
)
for {
oldCheckpointTs := subStat.checkpointTs.Load()
if newCheckpointTs == oldCheckpointTs {
return
}
}
e.subscriptionChangeCh.In() <- SubscriptionChange{
ChangeType: SubscriptionChangeTypeUpdate,
SubID: uint64(subStat.subID),
Span: subStat.tableSpan,
CheckpointTs: newCheckpointTs,
ResolvedTs: subStat.resolvedTs.Load(),
}
subStat.checkpointTs.Store(newCheckpointTs)
if log.GetLevel() <= zap.DebugLevel {
log.Debug("update checkpoint ts",
zap.Any("dispatcherID", dispatcherID),
zap.Uint64("subscriptionID", uint64(subStat.subID)),
zap.Uint64("newCheckpointTs", newCheckpointTs),
zap.Uint64("oldCheckpointTs", oldCheckpointTs))
if newCheckpointTs < oldCheckpointTs {
return
}
if !subStat.checkpointTs.CompareAndSwap(oldCheckpointTs, newCheckpointTs) {
continue
}
e.gcManager.addGCItem(
subStat.dbIndex,
uint64(subStat.subID),
subStat.tableSpan.TableID,
oldCheckpointTs,
newCheckpointTs,
)
e.subscriptionChangeCh.In() <- SubscriptionChange{
ChangeType: SubscriptionChangeTypeUpdate,
SubID: uint64(subStat.subID),
Span: subStat.tableSpan,
CheckpointTs: newCheckpointTs,
ResolvedTs: subStat.resolvedTs.Load(),
}
if log.GetLevel() <= zap.DebugLevel {
log.Debug("update checkpoint ts",
zap.Any("dispatcherID", dispatcherID),
zap.Uint64("subscriptionID", uint64(subStat.subID)),
zap.Uint64("newCheckpointTs", newCheckpointTs),
zap.Uint64("oldCheckpointTs", oldCheckpointTs))
}
return
}
}
updateSubStatCheckpoint(dispatcherStat.subStat)
Expand Down Expand Up @@ -1501,7 +1497,7 @@ func (iter *eventStoreIter) Next() (*common.RawKVEntry, bool) {
}
comparableKey := common.ToComparableKey(rawKV.Key)
if bytes.Compare(comparableKey, iter.tableSpan.StartKey) >= 0 &&
bytes.Compare(comparableKey, iter.tableSpan.EndKey) <= 0 {
bytes.Compare(comparableKey, iter.tableSpan.EndKey) < 0 {
break
}
log.Debug("event store iter skip kv not in table span",
Expand Down Expand Up @@ -1645,17 +1641,21 @@ func (e *eventStore) uploadStatePeriodically(ctx context.Context) error {
log.Warn("cannot find subscription state", zap.Uint64("subscriptionID", change.SubID))
continue
}
if change.CheckpointTs < tableState.Subscriptions[targetIndex].CheckpointTs ||
change.ResolvedTs < tableState.Subscriptions[targetIndex].ResolvedTs {
log.Panic("should not happen",
subState := tableState.Subscriptions[targetIndex]
if change.CheckpointTs < subState.CheckpointTs || change.ResolvedTs < subState.ResolvedTs {
log.Warn("ignore stale subscription state update",
zap.Uint64("subscriptionID", change.SubID),
zap.Uint64("oldCheckpointTs", tableState.Subscriptions[targetIndex].CheckpointTs),
zap.Uint64("oldResolvedTs", tableState.Subscriptions[targetIndex].ResolvedTs),
zap.Uint64("oldCheckpointTs", subState.CheckpointTs),
zap.Uint64("oldResolvedTs", subState.ResolvedTs),
zap.Uint64("newCheckpointTs", change.CheckpointTs),
zap.Uint64("newResolvedTs", change.ResolvedTs))
}
tableState.Subscriptions[targetIndex].CheckpointTs = change.CheckpointTs
tableState.Subscriptions[targetIndex].ResolvedTs = change.ResolvedTs
if change.CheckpointTs > subState.CheckpointTs {
subState.CheckpointTs = change.CheckpointTs
}
if change.ResolvedTs > subState.ResolvedTs {
subState.ResolvedTs = change.ResolvedTs
}
default:
log.Panic("invalid subscription change type", zap.Int("changeType", int(change.ChangeType)))
}
Expand Down
4 changes: 2 additions & 2 deletions logservice/eventstore/event_store_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1227,8 +1227,8 @@ func TestEventStoreIter_NextWithFiltering(t *testing.T) {
var tableID int64 = 42
iteratorSpan := &heartbeatpb.TableSpan{
TableID: tableID,
StartKey: []byte("keyB"),
EndKey: []byte("keyD"),
StartKey: common.ToComparableKey([]byte("keyB")),
EndKey: common.ToComparableKey([]byte("keyD")),
}

// This test now focuses on a single, more comprehensive scenario.
Expand Down