Skip FOR...UPDATE Clause in Warming Reads Queries

go/vt/vtgate/engine/route.go

@@ -508,6 +508,11 @@ func (route *Route) executeWarmingReplicaRead(ctx context.Context, vcursor VCurs
 		return
 	}
 
+	// Skip SELECT ... FOR UPDATE queries that cannot run on read-only replicas
+	if strings.Contains(strings.ToLower(route.Query), "for update") {
+		return
+	}
+
 	if vcursor.GetWarmingReadsPercent() == 0 || rand.IntN(100) > vcursor.GetWarmingReadsPercent() {
 		return
 	}

go/vt/vtgate/engine/route_warming_reads_test.go

@@ -0,0 +1,127 @@
+/*
+Copyright 2024 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package engine
+
+import (
+	"context"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"vitess.io/vitess/go/sqltypes"
+	"vitess.io/vitess/go/vt/srvtopo"
+	"vitess.io/vitess/go/vt/vtgate/evalengine"
+	"vitess.io/vitess/go/vt/vtgate/vindexes"
+
+	querypb "vitess.io/vitess/go/vt/proto/query"
+)
+
+type warmingReadsVCursor struct {
+	*loggingVCursor
+	warmingReadsPercent     int
+	warmingReadsChannel     chan bool
+	warmingReadsExecuteFunc func(context.Context, Primitive, []*srvtopo.ResolvedShard, []*querypb.BoundQuery, bool, bool)
+}
+
+func (vc *warmingReadsVCursor) GetWarmingReadsPercent() int {
+	return vc.warmingReadsPercent
+}
+
+func (vc *warmingReadsVCursor) GetWarmingReadsChannel() chan bool {
+	return vc.warmingReadsChannel
+}
+
+func (vc *warmingReadsVCursor) CloneForReplicaWarming(ctx context.Context) VCursor {
+	clone := &warmingReadsVCursor{
+		loggingVCursor:          vc.loggingVCursor,
+		warmingReadsPercent:     vc.warmingReadsPercent,
+		warmingReadsChannel:     vc.warmingReadsChannel,
+		warmingReadsExecuteFunc: vc.warmingReadsExecuteFunc,
+	}
+	clone.onExecuteMultiShardFn = vc.warmingReadsExecuteFunc
+	return clone
+}
+
+func TestWarmingReadsSkipsForUpdate(t *testing.T) {
+	vindex, _ := vindexes.CreateVindex("hash", "", nil)
+	testCases := []struct {
+		name       string
+		query      string
+		shouldSkip bool
+	}{
+		{
+			name:       "SELECT FOR UPDATE",
+			query:      "SELECT * FROM users WHERE id = 1 FOR UPDATE",
+			shouldSkip: true,
+		},
+		{
+			name:       "SELECT FOR UPDATE mixed case",
+			query:      "SELECT * FROM users WHERE id = 1 FoR UpDaTe",
+			shouldSkip: true,
+		},
+		{
+			name:       "Regular SELECT",
+			query:      "SELECT * FROM users WHERE id = 1",
+			shouldSkip: false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			route := NewRoute(
+				EqualUnique,
+				&vindexes.Keyspace{
+					Name:    "ks",
+					Sharded: true,
+				},
+				tc.query,
+				"dummy_select_field",
+			)
+			route.Vindex = vindex.(vindexes.SingleColumn)
+			route.Values = []evalengine.Expr{
+				evalengine.NewLiteralInt(1),
+			}
+
+			var warmingReadExecuted atomic.Bool
+			vc := &warmingReadsVCursor{
+				loggingVCursor: &loggingVCursor{
+					shards:  []string{"-20", "20-"},
+					results: []*sqltypes.Result{defaultSelectResult},
+				},
+				warmingReadsPercent: 100,
+				warmingReadsChannel: make(chan bool, 1),
+			}
+			vc.warmingReadsExecuteFunc = func(ctx context.Context, primitive Primitive, rss []*srvtopo.ResolvedShard, queries []*querypb.BoundQuery, rollbackOnError, canAutocommit bool) {
+				warmingReadExecuted.Store(true)
+			}
+
+			_, err := route.TryExecute(context.Background(), vc, map[string]*querypb.BindVariable{}, false)
+			require.NoError(t, err)
+
+			if tc.shouldSkip {
+				time.Sleep(50 * time.Millisecond)
+				require.False(t, warmingReadExecuted.Load(), "warming read should not be executed for FOR UPDATE queries")
+			} else {
+				require.Eventually(t, func() bool {
+					return warmingReadExecuted.Load()
+				}, time.Second, 10*time.Millisecond, "warming read should be executed for regular SELECT queries")
+			}
+		})
+	}
+}