sql: add cluster setting for merge batch size in index merger

Release note: None

pkg/sql/backfill.go

@@ -82,6 +82,17 @@ var indexBackfillBatchSize = settings.RegisterIntSetting(
 	settings.NonNegativeInt, /* validateFn */
 )
 
+// indexBackfillMergeBatchSize is the maximum number of rows we
+// attempt to merge in a single transaction during the merging
+// process.
+var indexBackfillMergeBatchSize = settings.RegisterIntSetting(
+	settings.TenantWritable,
+	"bulkio.index_backfill.merge_batch_size",
+	"the number of rows we merge between temporary and adding indexes in a single batch",
+	1000,
+	settings.NonNegativeInt, /* validateFn */
+)
+
 // columnBackfillBatchSize is the maximum number of rows we update at once when
 // adding or removing columns.
 var columnBackfillBatchSize = settings.RegisterIntSetting(

pkg/sql/mvcc_backfiller.go

@@ -63,7 +63,7 @@ func (im *IndexBackfillerMergePlanner) plan(
 		evalCtx = createSchemaChangeEvalCtx(ctx, im.execCfg, txn.ReadTimestamp(), descriptors)
 		planCtx = im.execCfg.DistSQLPlanner.NewPlanningCtx(ctx, &evalCtx, nil /* planner */, txn,
 			true /* distribute */)
-		chunkSize := indexBackfillBatchSize.Get(&im.execCfg.Settings.SV)
+		chunkSize := indexBackfillMergeBatchSize.Get(&im.execCfg.Settings.SV)
 
 		spec, err := initIndexBackfillMergerSpec(*tableDesc.TableDesc(), chunkSize, addedIndexes, temporaryIndexes)
 		if err != nil {

pkg/sql/mvcc_backfiller_test.go

@@ -268,7 +268,7 @@ func TestRaceWithIndexBackfillMerge(t *testing.T) {
 
 	// TODO(rui): use testing hook instead of cluster setting once this value for
 	// the backfill merge is hooked up to testing hooks.
-	if _, err := sqlDB.Exec(fmt.Sprintf(`SET CLUSTER SETTING bulkio.index_backfill.batch_size = %d`, chunkSize)); err != nil {
+	if _, err := sqlDB.Exec(fmt.Sprintf(`SET CLUSTER SETTING bulkio.index_backfill.merge_batch_size = %d`, chunkSize)); err != nil {
 		t.Fatal(err)
 	}