diff --git a/dashboard/app/batch_coverage.go b/dashboard/app/batch_coverage.go
index d5dc3b83f3ed..584d33505f56 100644
--- a/dashboard/app/batch_coverage.go
+++ b/dashboard/app/batch_coverage.go
@@ -7,11 +7,13 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"os"
 	"strconv"
 
 	"cloud.google.com/go/batch/apiv1/batchpb"
 	"cloud.google.com/go/bigquery"
 	"cloud.google.com/go/civil"
+	"cloud.google.com/go/spanner"
 	"github.com/google/syzkaller/pkg/coveragedb"
 	"google.golang.org/api/iterator"
 	"google.golang.org/appengine/v2"
@@ -151,3 +153,71 @@ func nsDataAvailable(ctx context.Context, ns string) ([]coveragedb.TimePeriod, [
 	}
 	return periods, recordsCount, nil
 }
+
+// Abandoned DB cleanup is expensive.
+// Every namespace creates min 3 sessions every day (yesterday, today, this month).
+// It means every day we deprecate 3 sessions records.
+// Every session is ~10k file records. Plus some mutations in the index.
+// One transaction allows to delete up to 80k rows.
+// To clean up everything once/week we have to garbage 7 * 3 * count(namespaces) at least.
+func handleBatchCoverageClean(w http.ResponseWriter, r *http.Request) {
+	paramSessions := r.FormValue("sessions")
+	if paramSessions == "" {
+		paramSessions = "3" // one day, one namespace means 3 records
+	}
+	maxSessionsToDel, err := strconv.Atoi(r.FormValue("sessions"))
+	if err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		w.Write([]byte("failed to parse 'sessions', integer expected"))
+		return
+	}
+	ctx := context.Background()
+	for i := 0; i < maxSessionsToDel; i++ {
+		deletedRows, err := deleteGarbageSession(ctx)
+		if err != nil {
+			errMsg := fmt.Sprintf("failed to cleanCoverageDB: %s", err.Error())
+			log.Errorf(ctx, errMsg)
+			w.Write([]byte(errMsg))
+			return
+		}
+		w.Write([]byte(fmt.Sprintf("deleteGarbageSession -> -%d rows\n", deletedRows)))
+	}
+}
+
+// deleteGarbageSession generates approximately 20k mutations (10k in files and 10k in index)
+// Spanner limit for every transaction is 80k mutations.
+// It means we can delete up to 4 sessions data at once.
+// Let's keep it simple and delete only 1 session at once.
+//
+// deleteGarbageSession returns the deleted rows count.
+// (0, nil) means there is no data to delete.
+func deleteGarbageSession(ctx context.Context) (int64, error) {
+	client, err := coveragedb.NewClient(ctx, os.Getenv("GOOGLE_CLOUD_PROJECT"))
+	if err != nil {
+		return 0, fmt.Errorf("failed to coveragedb.NewClient: %w", err)
+	}
+	defer client.Close()
+	var rowCount int64
+
+	_, err = client.ReadWriteTransaction(ctx, func(ctx context.Context, txn *spanner.ReadWriteTransaction) error {
+		stmt := spanner.Statement{
+			SQL: `	delete from files
+								where files.session in (
+									select
+										distinct(files.session)
+									from files
+									left join merge_history
+										on files.session = merge_history.session
+									where merge_history.session is NULL
+									limit 1
+								);`,
+		}
+		var err error
+		rowCount, err = txn.Update(ctx, stmt)
+		if err != nil {
+			return fmt.Errorf("txn.Update: %w", err)
+		}
+		return nil
+	})
+	return rowCount, err
+}
diff --git a/dashboard/app/batch_main.go b/dashboard/app/batch_main.go
index e1b514a26346..596f50e502f0 100644
--- a/dashboard/app/batch_main.go
+++ b/dashboard/app/batch_main.go
@@ -18,6 +18,7 @@ import (
 func initBatchProcessors() {
 	http.HandleFunc("/cron/batch_coverage", handleBatchCoverage)
 	http.HandleFunc("/cron/batch_db_export", handleBatchDBExport)
+	http.HandleFunc("/cron/batch_coverage_clean", handleBatchCoverageClean)
 }
 
 // from https://cloud.google.com/batch/docs/samples/batch-create-script-job
diff --git a/dashboard/app/cron.yaml b/dashboard/app/cron.yaml
index a0acdf7d2f02..31a57974ef75 100644
--- a/dashboard/app/cron.yaml
+++ b/dashboard/app/cron.yaml
@@ -24,7 +24,13 @@ cron:
   schedule: every sunday 00:00
 # Update other coverage numbers every day.
 - url: /cron/batch_coverage?days=true&months=true&steps=10
-  schedule: every 24 hours
+  schedule: every day 00:00
+# Clean up coverage db every week.
+# We're adding data w/o transactions.
+# It is important to run clean operation when there are no batch_coverage in progress.
+# Let's delete max 7 days * 3 namespaces * 3 new_sessions/day * 2 to_remove old too
+- url: /cron/batch_coverage_clean?sessions=126
+  schedule: every saturday 12:00
 # Export reproducers every week.
 - url: /cron/batch_db_export
   schedule: every saturday 00:00
diff --git a/tools/syz-covermerger/init_db.sh b/tools/syz-covermerger/init_db.sh
index d31f68e9ae8f..2af9a8aed23e 100755
--- a/tools/syz-covermerger/init_db.sh
+++ b/tools/syz-covermerger/init_db.sh
@@ -23,6 +23,9 @@ CREATE TABLE
     (session, filepath) );')
 gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \
  --ddl="$create_table"
+echo "creating 'files' index"
+gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \
+ --ddl="CREATE INDEX files_session ON files (session);"
 
 echo "drop table 'merge_history' if exists"
 gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \
@@ -43,6 +46,9 @@ CREATE TABLE
     (namespace, repo, duration, dateto) );')
 gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \
  --ddl="$create_table"
+ echo "creating 'merge_history' index"
+ gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \
+  --ddl="CREATE INDEX merge_history_session ON merge_history (session);"
 
 echo "drop table 'file_subsystems' if exists"
 gcloud spanner databases ddl update $db --instance=syzbot --project=syzkaller \