diff --git a/lib/mergeset/table.go b/lib/mergeset/table.go
index e646b9c87..4df0b82d1 100644
--- a/lib/mergeset/table.go
+++ b/lib/mergeset/table.go
@@ -59,6 +59,8 @@ const rawItemsFlushInterval = time.Second
 type Table struct {
 	path string
 
+	flushCallback func()
+
 	partsLock sync.Mutex
 	parts     []*partWrapper
 
@@ -121,8 +123,11 @@ func (pw *partWrapper) decRef() {
 
 // OpenTable opens a table on the given path.
 //
+// Optional flushCallback is called every time new data batch is flushed
+// to the underlying storage and becomes visible to search.
+//
 // The table is created if it doesn't exist yet.
-func OpenTable(path string) (*Table, error) {
+func OpenTable(path string, flushCallback func()) (*Table, error) {
 	path = filepath.Clean(path)
 	logger.Infof("opening table %q...", path)
 	startTime := time.Now()
@@ -145,11 +150,12 @@ func OpenTable(path string) (*Table, error) {
 	}
 
 	tb := &Table{
-		path:     path,
-		parts:    pws,
-		mergeIdx: uint64(time.Now().UnixNano()),
-		flockF:   flockF,
-		stopCh:   make(chan struct{}),
+		path:          path,
+		flushCallback: flushCallback,
+		parts:         pws,
+		mergeIdx:      uint64(time.Now().UnixNano()),
+		flockF:        flockF,
+		stopCh:        make(chan struct{}),
 	}
 	tb.startPartMergers()
 	tb.startRawItemsFlusher()
@@ -444,6 +450,9 @@ func (tb *Table) mergeRawItemsBlocks(blocksToMerge []*inmemoryBlock) {
 		if err := tb.mergeParts(pws, nil, true); err != nil {
 			logger.Panicf("FATAL: cannot merge raw parts: %s", err)
 		}
+		if tb.flushCallback != nil {
+			tb.flushCallback()
+		}
 	}
 
 	for {
diff --git a/lib/mergeset/table_search_test.go b/lib/mergeset/table_search_test.go
index fb09d5f2b..cfb721bb9 100644
--- a/lib/mergeset/table_search_test.go
+++ b/lib/mergeset/table_search_test.go
@@ -5,6 +5,7 @@ import (
 	"math/rand"
 	"os"
 	"sort"
+	"sync/atomic"
 	"testing"
 	"time"
 )
@@ -39,7 +40,7 @@ func TestTableSearchSerial(t *testing.T) {
 
 	func() {
 		// Re-open the table and verify the search works.
-		tb, err := OpenTable(path)
+		tb, err := OpenTable(path, nil)
 		if err != nil {
 			t.Fatalf("cannot open table: %s", err)
 		}
@@ -74,7 +75,7 @@ func TestTableSearchConcurrent(t *testing.T) {
 
 	// Re-open the table and verify the search works.
 	func() {
-		tb, err := OpenTable(path)
+		tb, err := OpenTable(path, nil)
 		if err != nil {
 			t.Fatalf("cannot open table: %s", err)
 		}
@@ -146,7 +147,11 @@ func testTableSearchSerial(tb *Table, items []string) error {
 }
 
 func newTestTable(path string, itemsCount int) (*Table, []string, error) {
-	tb, err := OpenTable(path)
+	var flushes uint64
+	flushCallback := func() {
+		atomic.AddUint64(&flushes, 1)
+	}
+	tb, err := OpenTable(path, flushCallback)
 	if err != nil {
 		return nil, nil, fmt.Errorf("cannot open table: %s", err)
 	}
@@ -159,6 +164,9 @@ func newTestTable(path string, itemsCount int) (*Table, []string, error) {
 		items[i] = item
 	}
 	tb.DebugFlush()
+	if itemsCount > 0 && atomic.LoadUint64(&flushes) == 0 {
+		return nil, nil, fmt.Errorf("unexpeted zero flushes for itemsCount=%d", itemsCount)
+	}
 
 	sort.Strings(items)
 	return tb, items, nil
diff --git a/lib/mergeset/table_search_timing_test.go b/lib/mergeset/table_search_timing_test.go
index ddafc9728..16c2f6035 100644
--- a/lib/mergeset/table_search_timing_test.go
+++ b/lib/mergeset/table_search_timing_test.go
@@ -32,7 +32,7 @@ func benchmarkTableSearch(b *testing.B, itemsCount int) {
 
 	// Force finishing pending merges
 	tb.MustClose()
-	tb, err = OpenTable(path)
+	tb, err = OpenTable(path, nil)
 	if err != nil {
 		b.Fatalf("unexpected error when re-opening table %q: %s", path, err)
 	}
diff --git a/lib/mergeset/table_test.go b/lib/mergeset/table_test.go
index aeb658c77..db063f1eb 100644
--- a/lib/mergeset/table_test.go
+++ b/lib/mergeset/table_test.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"sync"
+	"sync/atomic"
 	"testing"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
@@ -20,7 +21,7 @@ func TestTableOpenClose(t *testing.T) {
 	}()
 
 	// Create a new table
-	tb, err := OpenTable(path)
+	tb, err := OpenTable(path, nil)
 	if err != nil {
 		t.Fatalf("cannot create new table: %s", err)
 	}
@@ -30,7 +31,7 @@ func TestTableOpenClose(t *testing.T) {
 
 	// Re-open created table multiple times.
 	for i := 0; i < 10; i++ {
-		tb, err := OpenTable(path)
+		tb, err := OpenTable(path, nil)
 		if err != nil {
 			t.Fatalf("cannot open created table: %s", err)
 		}
@@ -44,14 +45,14 @@ func TestTableOpenMultipleTimes(t *testing.T) {
 		_ = os.RemoveAll(path)
 	}()
 
-	tb1, err := OpenTable(path)
+	tb1, err := OpenTable(path, nil)
 	if err != nil {
 		t.Fatalf("cannot open table: %s", err)
 	}
 	defer tb1.MustClose()
 
 	for i := 0; i < 10; i++ {
-		tb2, err := OpenTable(path)
+		tb2, err := OpenTable(path, nil)
 		if err == nil {
 			tb2.MustClose()
 			t.Fatalf("expecting non-nil error when opening already opened table")
@@ -68,7 +69,11 @@ func TestTableAddItemSerial(t *testing.T) {
 		_ = os.RemoveAll(path)
 	}()
 
-	tb, err := OpenTable(path)
+	var flushes uint64
+	flushCallback := func() {
+		atomic.AddUint64(&flushes, 1)
+	}
+	tb, err := OpenTable(path, flushCallback)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -78,6 +83,9 @@ func TestTableAddItemSerial(t *testing.T) {
 
 	// Verify items count after pending items flush.
 	tb.DebugFlush()
+	if atomic.LoadUint64(&flushes) == 0 {
+		t.Fatalf("unexpected zero flushes")
+	}
 
 	var m TableMetrics
 	tb.UpdateMetrics(&m)
@@ -91,7 +99,7 @@ func TestTableAddItemSerial(t *testing.T) {
 	testReopenTable(t, path, itemsCount)
 
 	// Add more items in order to verify merge between inmemory parts and file-based parts.
-	tb, err = OpenTable(path)
+	tb, err = OpenTable(path, nil)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -124,7 +132,7 @@ func TestTableCreateSnapshotAt(t *testing.T) {
 		_ = os.RemoveAll(path)
 	}()
 
-	tb, err := OpenTable(path)
+	tb, err := OpenTable(path, nil)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -155,13 +163,13 @@ func TestTableCreateSnapshotAt(t *testing.T) {
 	}()
 
 	// Verify snapshots contain all the data.
-	tb1, err := OpenTable(snapshot1)
+	tb1, err := OpenTable(snapshot1, nil)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
 	defer tb1.MustClose()
 
-	tb2, err := OpenTable(snapshot2)
+	tb2, err := OpenTable(snapshot2, nil)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -205,7 +213,11 @@ func TestTableAddItemsConcurrent(t *testing.T) {
 		_ = os.RemoveAll(path)
 	}()
 
-	tb, err := OpenTable(path)
+	var flushes uint64
+	flushCallback := func() {
+		atomic.AddUint64(&flushes, 1)
+	}
+	tb, err := OpenTable(path, flushCallback)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -215,6 +227,10 @@ func TestTableAddItemsConcurrent(t *testing.T) {
 
 	// Verify items count after pending items flush.
 	tb.DebugFlush()
+	if atomic.LoadUint64(&flushes) == 0 {
+		t.Fatalf("unexpected zero flushes")
+	}
+
 	var m TableMetrics
 	tb.UpdateMetrics(&m)
 	if m.ItemsCount != itemsCount {
@@ -227,7 +243,7 @@ func TestTableAddItemsConcurrent(t *testing.T) {
 	testReopenTable(t, path, itemsCount)
 
 	// Add more items in order to verify merge between inmemory parts and file-based parts.
-	tb, err = OpenTable(path)
+	tb, err = OpenTable(path, nil)
 	if err != nil {
 		t.Fatalf("cannot open %q: %s", path, err)
 	}
@@ -269,7 +285,7 @@ func testReopenTable(t *testing.T, path string, itemsCount int) {
 	t.Helper()
 
 	for i := 0; i < 10; i++ {
-		tb, err := OpenTable(path)
+		tb, err := OpenTable(path, nil)
 		if err != nil {
 			t.Fatalf("cannot re-open %q: %s", path, err)
 		}
diff --git a/lib/storage/index_db.go b/lib/storage/index_db.go
index 86b0bf41c..73af080b7 100644
--- a/lib/storage/index_db.go
+++ b/lib/storage/index_db.go
@@ -65,9 +65,6 @@ type indexDB struct {
 	// matching low number of metrics.
 	uselessTagFiltersCache *workingsetcache.Cache
 
-	tagCachePrefixes     map[accountProjectKey]uint64
-	tagCachePrefixesLock sync.RWMutex
-
 	indexSearchPool sync.Pool
 
 	// An inmemory map[uint64]struct{} of deleted metricIDs.
@@ -104,12 +101,6 @@ type indexDB struct {
 	mustDrop uint64
 }
 
-// accountProjectKey is used for maps keyed by (AccountID, ProjectID).
-type accountProjectKey struct {
-	AccountID uint32
-	ProjectID uint32
-}
-
 // openIndexDB opens index db from the given path with the given caches.
 func openIndexDB(path string, metricIDCache, metricNameCache *workingsetcache.Cache, currHourMetricIDs, prevHourMetricIDs *atomic.Value) (*indexDB, error) {
 	if metricIDCache == nil {
@@ -125,7 +116,7 @@ func openIndexDB(path string, metricIDCache, metricNameCache *workingsetcache.Ca
 		logger.Panicf("BUG: prevHourMetricIDs must be non-nil")
 	}
 
-	tb, err := mergeset.OpenTable(path)
+	tb, err := mergeset.OpenTable(path, invalidateTagCache)
 	if err != nil {
 		return nil, fmt.Errorf("cannot open indexDB %q: %s", path, err)
 	}
@@ -145,8 +136,6 @@ func openIndexDB(path string, metricIDCache, metricNameCache *workingsetcache.Ca
 		metricNameCache:        metricNameCache,
 		uselessTagFiltersCache: workingsetcache.New(mem/128, time.Hour),
 
-		tagCachePrefixes: make(map[accountProjectKey]uint64),
-
 		currHourMetricIDs: currHourMetricIDs,
 		prevHourMetricIDs: prevHourMetricIDs,
 	}
@@ -377,27 +366,17 @@ func (db *indexDB) putMetricNameToCache(metricID uint64, metricName []byte) {
 	db.metricNameCache.Set(key[:], metricName)
 }
 
-func (db *indexDB) marshalTagFiltersKey(dst []byte, tfss []*TagFilters, versioned bool) []byte {
-	if len(tfss) == 0 {
-		return nil
-	}
+func marshalTagFiltersKey(dst []byte, tfss []*TagFilters, versioned bool) []byte {
 	prefix := ^uint64(0)
 	if versioned {
-		k := accountProjectKey{
-			AccountID: tfss[0].accountID,
-			ProjectID: tfss[0].projectID,
-		}
-		db.tagCachePrefixesLock.RLock()
-		prefix = db.tagCachePrefixes[k]
-		db.tagCachePrefixesLock.RUnlock()
-		if prefix == 0 {
-			// Create missing prefix.
-			// It is OK if multiple concurrent goroutines call invalidateTagCache
-			// for the same (accountID, projectID).
-			prefix = db.invalidateTagCache(k.AccountID, k.ProjectID)
-		}
+		prefix = atomic.LoadUint64(&tagFiltersKeyGen)
 	}
 	dst = encoding.MarshalUint64(dst, prefix)
+	if len(tfss) == 0 {
+		return dst
+	}
+	dst = encoding.MarshalUint32(dst, tfss[0].accountID)
+	dst = encoding.MarshalUint32(dst, tfss[0].projectID)
 	for _, tfs := range tfss {
 		dst = append(dst, 0) // separator between tfs groups.
 		for i := range tfs.tfs {
@@ -439,21 +418,13 @@ func unmarshalTSIDs(dst []TSID, src []byte) ([]TSID, error) {
 	return dst, nil
 }
 
-func (db *indexDB) invalidateTagCache(accountID, projectID uint32) uint64 {
+func invalidateTagCache() {
 	// This function must be fast, since it is called each
 	// time new timeseries is added.
-	prefix := atomic.AddUint64(&tagCacheKeyPrefix, 1)
-	k := accountProjectKey{
-		AccountID: accountID,
-		ProjectID: projectID,
-	}
-	db.tagCachePrefixesLock.Lock()
-	db.tagCachePrefixes[k] = prefix
-	db.tagCachePrefixesLock.Unlock()
-	return prefix
+	atomic.AddUint64(&tagFiltersKeyGen, 1)
 }
 
-var tagCacheKeyPrefix uint64
+var tagFiltersKeyGen uint64
 
 // getTSIDByNameNoCreate fills the dst with TSID for the given metricName.
 //
@@ -555,9 +526,8 @@ func (db *indexDB) createTSIDByName(dst *TSID, metricName []byte) error {
 		return fmt.Errorf("cannot create indexes: %s", err)
 	}
 
-	// Invalidate tag cache for the given (AccountID, ProjectID), since
-	// it doesn't contain tags for the created mn -> TSID mapping.
-	_ = db.invalidateTagCache(mn.AccountID, mn.ProjectID)
+	// There is no need in invalidating tag cache, since it is invalidated
+	// on db.tb flush via invalidateTagCache flushCallback passed to OpenTable.
 
 	return nil
 }
@@ -904,8 +874,6 @@ func (db *indexDB) DeleteTSIDs(tfss []*TagFilters) (int, error) {
 	if len(tfss) == 0 {
 		return 0, nil
 	}
-	accountID := tfss[0].accountID
-	projectID := tfss[0].projectID
 
 	// Obtain metricIDs to delete.
 	is := db.getIndexSearch()
@@ -937,7 +905,7 @@ func (db *indexDB) DeleteTSIDs(tfss []*TagFilters) (int, error) {
 	db.updateDeletedMetricIDs(metricIDs)
 
 	// Reset TagFilters -> TSIDS cache, since it may contain deleted TSIDs.
-	_ = db.invalidateTagCache(accountID, projectID)
+	invalidateTagCache()
 
 	// Do not reset uselessTagFiltersCache, since the found metricIDs
 	// on cache miss are filtered out later with deletedMetricIDs.
@@ -1010,7 +978,7 @@ func (db *indexDB) searchTSIDs(tfss []*TagFilters, tr TimeRange, maxMetrics int)
 	tfKeyBuf := tagFiltersKeyBufPool.Get()
 	defer tagFiltersKeyBufPool.Put(tfKeyBuf)
 
-	tfKeyBuf.B = db.marshalTagFiltersKey(tfKeyBuf.B[:0], tfss, true)
+	tfKeyBuf.B = marshalTagFiltersKey(tfKeyBuf.B[:0], tfss, true)
 	tsids, ok := db.getFromTagCache(tfKeyBuf.B)
 	if ok {
 		// Fast path - tsids found in the cache.
@@ -1031,7 +999,7 @@ func (db *indexDB) searchTSIDs(tfss []*TagFilters, tr TimeRange, maxMetrics int)
 		defer tagFiltersKeyBufPool.Put(tfKeyExtBuf)
 
 		// Data in extDB cannot be changed, so use unversioned keys for tag cache.
-		tfKeyExtBuf.B = extDB.marshalTagFiltersKey(tfKeyExtBuf.B[:0], tfss, false)
+		tfKeyExtBuf.B = marshalTagFiltersKey(tfKeyExtBuf.B[:0], tfss, false)
 		tsids, ok := extDB.getFromTagCache(tfKeyExtBuf.B)
 		if ok {
 			extTSIDs = tsids
diff --git a/lib/storage/index_db_test.go b/lib/storage/index_db_test.go
index a87fce975..4c7a2880e 100644
--- a/lib/storage/index_db_test.go
+++ b/lib/storage/index_db_test.go
@@ -339,6 +339,10 @@ func testIndexDBCheckTSIDByName(db *indexDB, mns []MetricName, tsids []TSID, isC
 		return false
 	}
 
+	type accountProjectKey struct {
+		AccountID uint32
+		ProjectID uint32
+	}
 	allKeys := make(map[accountProjectKey]map[string]bool)
 	timeseriesCounters := make(map[accountProjectKey]map[uint64]bool)
 	var tsidCopy TSID