diff --git a/server/storage/mvcc/watchable_store.go b/server/storage/mvcc/watchable_store.go
index 22d46e5048d..ee47c2c6d72 100644
--- a/server/storage/mvcc/watchable_store.go
+++ b/server/storage/mvcc/watchable_store.go
@@ -221,6 +221,7 @@ func (s *watchableStore) syncWatchersLoop() {
 	waitDuration := 100 * time.Millisecond
 	delayTicker := time.NewTicker(waitDuration)
 	defer delayTicker.Stop()
+	var evs []mvccpb.Event
 
 	for {
 		s.mu.RLock()
@@ -230,7 +231,7 @@ func (s *watchableStore) syncWatchersLoop() {
 
 		unsyncedWatchers := 0
 		if lastUnsyncedWatchers > 0 {
-			unsyncedWatchers = s.syncWatchers()
+			unsyncedWatchers, evs = s.syncWatchers(evs)
 		}
 		syncDuration := time.Since(st)
 
@@ -339,12 +340,12 @@ func (s *watchableStore) moveVictims() (moved int) {
 //  2. iterate over the set to get the minimum revision and remove compacted watchers
 //  3. use minimum revision to get all key-value pairs and send those events to watchers
 //  4. remove synced watchers in set from unsynced group and move to synced group
-func (s *watchableStore) syncWatchers() int {
+func (s *watchableStore) syncWatchers(evs []mvccpb.Event) (int, []mvccpb.Event) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
 	if s.unsynced.size() == 0 {
-		return 0
+		return 0, []mvccpb.Event{}
 	}
 
 	s.store.revMu.RLock()
@@ -357,20 +358,7 @@ func (s *watchableStore) syncWatchers() int {
 	compactionRev := s.store.compactMainRev
 
 	wg, minRev := s.unsynced.choose(maxWatchersPerSync, curRev, compactionRev)
-	minBytes, maxBytes := NewRevBytes(), NewRevBytes()
-	minBytes = RevToBytes(Revision{Main: minRev}, minBytes)
-	maxBytes = RevToBytes(Revision{Main: curRev + 1}, maxBytes)
-
-	// UnsafeRange returns keys and values. And in boltdb, keys are revisions.
-	// values are actual key-value pairs in backend.
-	tx := s.store.b.ReadTx()
-	tx.RLock()
-	revs, vs := tx.UnsafeRange(schema.Key, minBytes, maxBytes, 0)
-	evs := kvsToEvents(s.store.lg, wg, revs, vs)
-	// Must unlock after kvsToEvents, because vs (come from boltdb memory) is not deep copy.
-	// We can only unlock after Unmarshal, which will do deep copy.
-	// Otherwise we will trigger SIGSEGV during boltdb re-mmap.
-	tx.RUnlock()
+	evs = rangeEventsWithReuse(s.store.lg, s.store.b, evs, minRev, curRev+1)
 
 	victims := make(watcherBatch)
 	wb := newWatcherBatch(wg, evs)
@@ -419,21 +407,68 @@ func (s *watchableStore) syncWatchers() int {
 	}
 	slowWatcherGauge.Set(float64(s.unsynced.size() + vsz))
 
-	return s.unsynced.size()
+	return s.unsynced.size(), evs
+}
+
+// rangeEventsWithReuse returns events in range [minRev, maxRev), while reusing already provided events.
+func rangeEventsWithReuse(lg *zap.Logger, b backend.Backend, evs []mvccpb.Event, minRev, maxRev int64) []mvccpb.Event {
+	if len(evs) == 0 {
+		return rangeEvents(lg, b, minRev, maxRev)
+	}
+	// append from left
+	if evs[0].Kv.ModRevision > minRev {
+		evs = append(rangeEvents(lg, b, minRev, evs[0].Kv.ModRevision), evs...)
+	}
+	// cut from left
+	prefixIndex := 0
+	for prefixIndex < len(evs) && evs[prefixIndex].Kv.ModRevision < minRev {
+		prefixIndex++
+	}
+	evs = evs[prefixIndex:]
+
+	if len(evs) == 0 {
+		return rangeEvents(lg, b, minRev, maxRev)
+	}
+	// append from right
+	if evs[len(evs)-1].Kv.ModRevision+1 < maxRev {
+		evs = append(evs, rangeEvents(lg, b, evs[len(evs)-1].Kv.ModRevision+1, maxRev)...)
+	}
+	// cut from right
+	suffixIndex := len(evs) - 1
+	for suffixIndex >= 0 && evs[suffixIndex].Kv.ModRevision >= maxRev {
+		suffixIndex--
+	}
+	evs = evs[:suffixIndex+1]
+	return evs
+}
+
+// rangeEvents returns events in range [minRev, maxRev).
+func rangeEvents(lg *zap.Logger, b backend.Backend, minRev, maxRev int64) []mvccpb.Event {
+	minBytes, maxBytes := NewRevBytes(), NewRevBytes()
+	minBytes = RevToBytes(Revision{Main: minRev}, minBytes)
+	maxBytes = RevToBytes(Revision{Main: maxRev}, maxBytes)
+
+	// UnsafeRange returns keys and values. And in boltdb, keys are revisions.
+	// values are actual key-value pairs in backend.
+	tx := b.ReadTx()
+	tx.RLock()
+	revs, vs := tx.UnsafeRange(schema.Key, minBytes, maxBytes, 0)
+	evs := kvsToEvents(lg, revs, vs)
+	// Must unlock after kvsToEvents, because vs (come from boltdb memory) is not deep copy.
+	// We can only unlock after Unmarshal, which will do deep copy.
+	// Otherwise we will trigger SIGSEGV during boltdb re-mmap.
+	tx.RUnlock()
+	return evs
 }
 
 // kvsToEvents gets all events for the watchers from all key-value pairs
-func kvsToEvents(lg *zap.Logger, wg *watcherGroup, revs, vals [][]byte) (evs []mvccpb.Event) {
+func kvsToEvents(lg *zap.Logger, revs, vals [][]byte) (evs []mvccpb.Event) {
 	for i, v := range vals {
 		var kv mvccpb.KeyValue
 		if err := kv.Unmarshal(v); err != nil {
 			lg.Panic("failed to unmarshal mvccpb.KeyValue", zap.Error(err))
 		}
 
-		if !wg.contains(string(kv.Key)) {
-			continue
-		}
-
 		ty := mvccpb.PUT
 		if isTombstone(revs[i]) {
 			ty = mvccpb.DELETE
diff --git a/server/storage/mvcc/watchable_store_test.go b/server/storage/mvcc/watchable_store_test.go
index c15bd12326f..a418c6c78fe 100644
--- a/server/storage/mvcc/watchable_store_test.go
+++ b/server/storage/mvcc/watchable_store_test.go
@@ -141,7 +141,7 @@ func TestSyncWatchers(t *testing.T) {
 
 	assert.Empty(t, s.synced.watcherSetByKey(string(testKey)))
 	assert.Len(t, s.unsynced.watcherSetByKey(string(testKey)), watcherN)
-	s.syncWatchers()
+	s.syncWatchers([]mvccpb.Event{})
 	assert.Len(t, s.synced.watcherSetByKey(string(testKey)), watcherN)
 	assert.Empty(t, s.unsynced.watcherSetByKey(string(testKey)))
 
@@ -164,6 +164,110 @@ func TestSyncWatchers(t *testing.T) {
 	}
 }
 
+func TestRangeEvents(t *testing.T) {
+	b, _ := betesting.NewDefaultTmpBackend(t)
+	lg := zaptest.NewLogger(t)
+	s := NewStore(lg, b, &lease.FakeLessor{}, StoreConfig{})
+
+	defer cleanup(s, b)
+
+	foo1 := []byte("foo1")
+	foo2 := []byte("foo2")
+	foo3 := []byte("foo3")
+	value := []byte("bar")
+	s.Put(foo1, value, lease.NoLease)
+	s.Put(foo2, value, lease.NoLease)
+	s.Put(foo3, value, lease.NoLease)
+	s.DeleteRange(foo1, foo3) // Deletes "foo1" and "foo2" generating 2 events
+
+	expectEvents := []mvccpb.Event{
+		{
+			Type: mvccpb.PUT,
+			Kv: &mvccpb.KeyValue{
+				Key:            foo1,
+				CreateRevision: 2,
+				ModRevision:    2,
+				Version:        1,
+				Value:          value,
+			},
+		},
+		{
+			Type: mvccpb.PUT,
+			Kv: &mvccpb.KeyValue{
+				Key:            foo2,
+				CreateRevision: 3,
+				ModRevision:    3,
+				Version:        1,
+				Value:          value,
+			},
+		},
+		{
+			Type: mvccpb.PUT,
+			Kv: &mvccpb.KeyValue{
+				Key:            foo3,
+				CreateRevision: 4,
+				ModRevision:    4,
+				Version:        1,
+				Value:          value,
+			},
+		},
+		{
+			Type: mvccpb.DELETE,
+			Kv: &mvccpb.KeyValue{
+				Key:         foo1,
+				ModRevision: 5,
+			},
+		},
+		{
+			Type: mvccpb.DELETE,
+			Kv: &mvccpb.KeyValue{
+				Key:         foo2,
+				ModRevision: 5,
+			},
+		},
+	}
+
+	tcs := []struct {
+		minRev       int64
+		maxRev       int64
+		expectEvents []mvccpb.Event
+	}{
+		// maxRev, top to bottom
+		{minRev: 2, maxRev: 6, expectEvents: expectEvents[0:5]},
+		{minRev: 2, maxRev: 5, expectEvents: expectEvents[0:3]},
+		{minRev: 2, maxRev: 4, expectEvents: expectEvents[0:2]},
+		{minRev: 2, maxRev: 3, expectEvents: expectEvents[0:1]},
+		{minRev: 2, maxRev: 2, expectEvents: expectEvents[0:0]},
+
+		// minRev, bottom to top
+		{minRev: 2, maxRev: 6, expectEvents: expectEvents[0:5]},
+		{minRev: 3, maxRev: 6, expectEvents: expectEvents[1:5]},
+		{minRev: 4, maxRev: 6, expectEvents: expectEvents[2:5]},
+		{minRev: 5, maxRev: 6, expectEvents: expectEvents[3:5]},
+		{minRev: 6, maxRev: 6, expectEvents: expectEvents[0:0]},
+
+		// Moving window algorithm, first increase maxRev, then increase minRev, repeat.
+		{minRev: 2, maxRev: 2, expectEvents: expectEvents[0:0]},
+		{minRev: 2, maxRev: 3, expectEvents: expectEvents[0:1]},
+		{minRev: 2, maxRev: 4, expectEvents: expectEvents[0:2]},
+		{minRev: 3, maxRev: 4, expectEvents: expectEvents[1:2]},
+		{minRev: 3, maxRev: 5, expectEvents: expectEvents[1:3]},
+		{minRev: 4, maxRev: 5, expectEvents: expectEvents[2:3]},
+		{minRev: 4, maxRev: 6, expectEvents: expectEvents[2:5]},
+		{minRev: 5, maxRev: 6, expectEvents: expectEvents[3:5]},
+		{minRev: 6, maxRev: 6, expectEvents: expectEvents[5:5]},
+	}
+	// reuse the evs to test rangeEventsWithReuse
+	var evs []mvccpb.Event
+	for i, tc := range tcs {
+		t.Run(fmt.Sprintf("%d rangeEvents(%d, %d)", i, tc.minRev, tc.maxRev), func(t *testing.T) {
+			assert.ElementsMatch(t, tc.expectEvents, rangeEvents(lg, b, tc.minRev, tc.maxRev))
+			evs = rangeEventsWithReuse(lg, b, evs, tc.minRev, tc.maxRev)
+			assert.ElementsMatch(t, tc.expectEvents, evs)
+		})
+	}
+}
+
 // TestWatchCompacted tests a watcher that watches on a compacted revision.
 func TestWatchCompacted(t *testing.T) {
 	b, _ := betesting.NewDefaultTmpBackend(t)
@@ -236,7 +340,7 @@ func TestWatchNoEventLossOnCompact(t *testing.T) {
 		require.NoError(t, err)
 	}
 	// fill up w.Chan() with 1 buf via 2 compacted watch response
-	s.syncWatchers()
+	s.syncWatchers([]mvccpb.Event{})
 
 	for len(watchers) > 0 {
 		resp := <-w.Chan()
diff --git a/server/storage/mvcc/watcher_test.go b/server/storage/mvcc/watcher_test.go
index 0c1fa521267..e774c70cfac 100644
--- a/server/storage/mvcc/watcher_test.go
+++ b/server/storage/mvcc/watcher_test.go
@@ -320,7 +320,7 @@ func TestWatcherRequestProgress(t *testing.T) {
 	default:
 	}
 
-	s.syncWatchers()
+	s.syncWatchers([]mvccpb.Event{})
 
 	w.RequestProgress(id)
 	wrs := WatchResponse{WatchID: id, Revision: 2}
@@ -359,7 +359,7 @@ func TestWatcherRequestProgressAll(t *testing.T) {
 	default:
 	}
 
-	s.syncWatchers()
+	s.syncWatchers([]mvccpb.Event{})
 
 	w.RequestProgressAll()
 	wrs := WatchResponse{WatchID: clientv3.InvalidWatchID, Revision: 2}