diff --git a/lib/storage/index_db.go b/lib/storage/index_db.go
index 415ca76fd..a0fb9d521 100644
--- a/lib/storage/index_db.go
+++ b/lib/storage/index_db.go
@@ -102,6 +102,19 @@ type indexDB struct {
 
 // openIndexDB opens index db from the given path with the given caches.
 func openIndexDB(path string, metricIDCache, metricNameCache *fastcache.Cache, currHourMetricIDs, prevHourMetricIDs *atomic.Value) (*indexDB, error) {
+	if metricIDCache == nil {
+		logger.Panicf("BUG: metricIDCache must be non-nil")
+	}
+	if metricNameCache == nil {
+		logger.Panicf("BUG: metricNameCache must be non-nil")
+	}
+	if currHourMetricIDs == nil {
+		logger.Panicf("BUG: currHourMetricIDs must be non-nil")
+	}
+	if prevHourMetricIDs == nil {
+		logger.Panicf("BUG: prevHourMetricIDs must be non-nil")
+	}
+
 	tb, err := mergeset.OpenTable(path)
 	if err != nil {
 		return nil, fmt.Errorf("cannot open indexDB %q: %s", path, err)
@@ -1251,11 +1264,8 @@ func (is *indexSearch) getTagFilterWithMinMetricIDsCountAdaptive(tfs *TagFilters
 var errTooManyMetrics = errors.New("all the tag filters match too many metrics")
 
 func (is *indexSearch) adjustMaxMetricsAdaptive(maxMetrics int) int {
-	if is.db.prevHourMetricIDs == nil {
-		return maxMetrics
-	}
 	hmPrev := is.db.prevHourMetricIDs.Load().(*hourMetricIDs)
-	if hmPrev == nil || !hmPrev.isFull {
+	if !hmPrev.isFull {
 		return maxMetrics
 	}
 	hourMetrics := len(hmPrev.m)
@@ -1678,9 +1688,6 @@ func (is *indexSearch) getMetricIDsForTimeRange(tr TimeRange, maxMetrics int) (m
 func (is *indexSearch) getMetricIDsForRecentHours(tr TimeRange, maxMetrics int) (map[uint64]struct{}, bool) {
 	minHour := uint64(tr.MinTimestamp) / msecPerHour
 	maxHour := uint64(tr.MaxTimestamp) / msecPerHour
-	if is.db.currHourMetricIDs == nil {
-		return nil, false
-	}
 	hmCurr := is.db.currHourMetricIDs.Load().(*hourMetricIDs)
 	if maxHour == hmCurr.hour && minHour == maxHour && hmCurr.isFull {
 		// The tr fits the current hour.
@@ -1691,9 +1698,6 @@ func (is *indexSearch) getMetricIDsForRecentHours(tr TimeRange, maxMetrics int)
 		}
 		return getMetricIDsCopy(hmCurr.m), true
 	}
-	if is.db.prevHourMetricIDs == nil {
-		return nil, false
-	}
 	hmPrev := is.db.prevHourMetricIDs.Load().(*hourMetricIDs)
 	if maxHour == hmPrev.hour && minHour == maxHour && hmPrev.isFull {
 		// The tr fits the previous hour.
diff --git a/lib/storage/index_db_test.go b/lib/storage/index_db_test.go
index 6e35eacbc..fcb3dcf22 100644
--- a/lib/storage/index_db_test.go
+++ b/lib/storage/index_db_test.go
@@ -7,6 +7,7 @@ import (
 	"math/rand"
 	"os"
 	"reflect"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -60,8 +61,14 @@ func TestIndexDBOpenClose(t *testing.T) {
 	metricNameCache := fastcache.New(1234)
 	defer metricIDCache.Reset()
 	defer metricNameCache.Reset()
+
+	var hmCurr atomic.Value
+	hmCurr.Store(&hourMetricIDs{})
+	var hmPrev atomic.Value
+	hmPrev.Store(&hourMetricIDs{})
+
 	for i := 0; i < 5; i++ {
-		db, err := openIndexDB("test-index-db", metricIDCache, metricNameCache, nil, nil)
+		db, err := openIndexDB("test-index-db", metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 		if err != nil {
 			t.Fatalf("cannot open indexDB: %s", err)
 		}
@@ -82,8 +89,14 @@ func TestIndexDB(t *testing.T) {
 		metricNameCache := fastcache.New(1234)
 		defer metricIDCache.Reset()
 		defer metricNameCache.Reset()
+
+		var hmCurr atomic.Value
+		hmCurr.Store(&hourMetricIDs{})
+		var hmPrev atomic.Value
+		hmPrev.Store(&hourMetricIDs{})
+
 		dbName := "test-index-db-serial"
-		db, err := openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+		db, err := openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 		if err != nil {
 			t.Fatalf("cannot open indexDB: %s", err)
 		}
@@ -113,7 +126,7 @@ func TestIndexDB(t *testing.T) {
 
 		// Re-open the db and verify it works as expected.
 		db.MustClose()
-		db, err = openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+		db, err = openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 		if err != nil {
 			t.Fatalf("cannot open indexDB: %s", err)
 		}
@@ -133,8 +146,14 @@ func TestIndexDB(t *testing.T) {
 		metricNameCache := fastcache.New(1234)
 		defer metricIDCache.Reset()
 		defer metricNameCache.Reset()
+
+		var hmCurr atomic.Value
+		hmCurr.Store(&hourMetricIDs{})
+		var hmPrev atomic.Value
+		hmPrev.Store(&hourMetricIDs{})
+
 		dbName := "test-index-db-concurrent"
-		db, err := openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+		db, err := openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 		if err != nil {
 			t.Fatalf("cannot open indexDB: %s", err)
 		}
diff --git a/lib/storage/index_db_timing_test.go b/lib/storage/index_db_timing_test.go
index 4f03d925d..36f9e518d 100644
--- a/lib/storage/index_db_timing_test.go
+++ b/lib/storage/index_db_timing_test.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strconv"
+	"sync/atomic"
 	"testing"
 
 	"github.com/VictoriaMetrics/fastcache"
@@ -16,8 +17,14 @@ func BenchmarkIndexDBAddTSIDs(b *testing.B) {
 	metricNameCache := fastcache.New(1234)
 	defer metricIDCache.Reset()
 	defer metricNameCache.Reset()
+
+	var hmCurr atomic.Value
+	hmCurr.Store(&hourMetricIDs{})
+	var hmPrev atomic.Value
+	hmPrev.Store(&hourMetricIDs{})
+
 	const dbName = "bench-index-db-add-tsids"
-	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 	if err != nil {
 		b.Fatalf("cannot open indexDB: %s", err)
 	}
@@ -76,8 +83,14 @@ func BenchmarkIndexDBSearchTSIDs(b *testing.B) {
 	metricNameCache := fastcache.New(1234)
 	defer metricIDCache.Reset()
 	defer metricNameCache.Reset()
+
+	var hmCurr atomic.Value
+	hmCurr.Store(&hourMetricIDs{})
+	var hmPrev atomic.Value
+	hmPrev.Store(&hourMetricIDs{})
+
 	const dbName = "bench-index-db-search-tsids"
-	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 	if err != nil {
 		b.Fatalf("cannot open indexDB: %s", err)
 	}
@@ -145,8 +158,14 @@ func BenchmarkIndexDBGetTSIDs(b *testing.B) {
 	metricNameCache := fastcache.New(1234)
 	defer metricIDCache.Reset()
 	defer metricNameCache.Reset()
+
+	var hmCurr atomic.Value
+	hmCurr.Store(&hourMetricIDs{})
+	var hmPrev atomic.Value
+	hmPrev.Store(&hourMetricIDs{})
+
 	const dbName = "bench-index-db-get-tsids"
-	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, nil, nil)
+	db, err := openIndexDB(dbName, metricIDCache, metricNameCache, &hmCurr, &hmPrev)
 	if err != nil {
 		b.Fatalf("cannot open indexDB: %s", err)
 	}