diff --git a/lib/storage/index_db.go b/lib/storage/index_db.go
index de5408d5c4..6751a7f7f5 100644
--- a/lib/storage/index_db.go
+++ b/lib/storage/index_db.go
@@ -925,7 +925,7 @@ func (is *indexSearch) loadDeletedMetricIDs() (map[uint64]struct{}, error) {
 	return dmis, nil
 }
 
-// searchTSIDs returns tsids matching the given tfss over the given tr.
+// searchTSIDs returns sorted tsids matching the given tfss over the given tr.
 func (db *indexDB) searchTSIDs(tfss []*TagFilters, tr TimeRange, maxMetrics int) ([]TSID, error) {
 	if len(tfss) == 0 {
 		return nil, nil
diff --git a/lib/storage/part_search.go b/lib/storage/part_search.go
index 226a9ce9e9..777843842c 100644
--- a/lib/storage/part_search.go
+++ b/lib/storage/part_search.go
@@ -3,7 +3,9 @@ package storage
 import (
 	"fmt"
 	"io"
+	"os"
 	"sort"
+	"strings"
 
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/encoding"
@@ -49,7 +51,7 @@ type partSearch struct {
 func (ps *partSearch) reset() {
 	ps.Block.Reset()
 	ps.p = nil
-	ps.tsids = ps.tsids[:0]
+	ps.tsids = nil
 	ps.tsidIdx = 0
 	ps.fetchData = true
 	ps.metaindex = nil
@@ -64,16 +66,24 @@ func (ps *partSearch) reset() {
 	ps.err = nil
 }
 
+var isInTest = func() bool {
+	return strings.HasSuffix(os.Args[0], ".test")
+}()
+
 // Init initializes the ps with the given p, tsids and tr.
+//
+// tsids must be sorted.
+// tsids cannot be modified after the Init call, since it is owned by ps.
 func (ps *partSearch) Init(p *part, tsids []TSID, tr TimeRange, fetchData bool) {
 	ps.reset()
 	ps.p = p
 
 	if p.ph.MinTimestamp <= tr.MaxTimestamp && p.ph.MaxTimestamp >= tr.MinTimestamp {
-		if !sort.SliceIsSorted(tsids, func(i, j int) bool { return tsids[i].Less(&tsids[j]) }) {
+		if isInTest && !sort.SliceIsSorted(tsids, func(i, j int) bool { return tsids[i].Less(&tsids[j]) }) {
 			logger.Panicf("BUG: tsids must be sorted; got %+v", tsids)
 		}
-		ps.tsids = append(ps.tsids[:0], tsids...)
+		// take ownership of of tsids.
+		ps.tsids = tsids
 	}
 	ps.tr = tr
 	ps.fetchData = fetchData
diff --git a/lib/storage/partition_search.go b/lib/storage/partition_search.go
index 475ffed5ad..3e2ed4020c 100644
--- a/lib/storage/partition_search.go
+++ b/lib/storage/partition_search.go
@@ -55,7 +55,10 @@ func (pts *partitionSearch) reset() {
 
 // Init initializes the search in the given partition for the given tsid and tr.
 //
-// MustClose must be called when partition search is done.
+// tsids must be sorted.
+// tsids cannot be modified after the Init call, since it is owned by pts.
+//
+/// MustClose must be called when partition search is done.
 func (pts *partitionSearch) Init(pt *partition, tsids []TSID, tr TimeRange, fetchData bool) {
 	if pts.needClosing {
 		logger.Panicf("BUG: missing partitionSearch.MustClose call before the next call to Init")
diff --git a/lib/storage/storage.go b/lib/storage/storage.go
index 8a71a351b7..53e7edd1f7 100644
--- a/lib/storage/storage.go
+++ b/lib/storage/storage.go
@@ -579,7 +579,7 @@ func nextRetentionDuration(retentionMonths int) time.Duration {
 	return deadline.Sub(t)
 }
 
-// searchTSIDs returns TSIDs for the given tfss and the given tr.
+// searchTSIDs returns sorted TSIDs for the given tfss and the given tr.
 func (s *Storage) searchTSIDs(tfss []*TagFilters, tr TimeRange, maxMetrics int) ([]TSID, error) {
 	// Do not cache tfss -> tsids here, since the caching is performed
 	// on idb level.
diff --git a/lib/storage/table_search.go b/lib/storage/table_search.go
index aa5b814760..1f4f4ca56c 100644
--- a/lib/storage/table_search.go
+++ b/lib/storage/table_search.go
@@ -54,6 +54,9 @@ func (ts *tableSearch) reset() {
 
 // Init initializes the ts.
 //
+// tsids must be sorted.
+// tsids cannot be modified after the Init call, since it is owned by ts.
+//
 // MustClose must be called then the tableSearch is done.
 func (ts *tableSearch) Init(tb *table, tsids []TSID, tr TimeRange, fetchData bool) {
 	if ts.needClosing {