mvcc/kvstore:when the number key-value is greater than one million, compact take too long and blocks other requests

mvcc/kvstore.go

@@ -271,15 +271,15 @@ func (s *store) updateCompactRev(rev int64) (<-chan struct{}, error) {
 }
 
 func (s *store) compact(trace *traceutil.Trace, rev int64) (<-chan struct{}, error) {
-	start := time.Now()
-	keep := s.kvindex.Compact(rev)
-	trace.Step("compact in-memory index tree")
 	ch := make(chan struct{})
 	var j = func(ctx context.Context) {
 		if ctx.Err() != nil {
 			s.compactBarrier(ctx, ch)
 			return
 		}
+		start := time.Now()
+		keep := s.kvindex.Compact(rev)
+		indexCompactionPauseMs.Observe(float64(time.Since(start) / time.Millisecond))
 		if !s.scheduleCompaction(rev, keep) {
 			s.compactBarrier(nil, ch)
 			return
@@ -288,8 +288,6 @@ func (s *store) compact(trace *traceutil.Trace, rev int64) (<-chan struct{}, err
 	}
 
 	s.fifoSched.Schedule(j)
-
-	indexCompactionPauseMs.Observe(float64(time.Since(start) / time.Millisecond))
 	trace.Step("schedule compaction")
 	return ch, nil
 }