metrics(dm): ignore binlog gap for non-running tasks

dm/metrics/alertmanager/dm_worker.rules.yml

@@ -125,12 +125,12 @@ groups:
       summary: dm relay binlog file not catch up master server exceed 10 min
 
   - alert: DM_binlog_file_gap_between_master_syncer
-    expr: dm_syncer_binlog_file{node="master"} - ON(instance, task, job) dm_syncer_binlog_file{node="syncer"} > 1
+    expr: (dm_syncer_binlog_file{node="master"} - ON(instance, task, job) dm_syncer_binlog_file{node="syncer"} > 1) and ON(instance, task, job) (dm_worker_task_state == 2)
     for: 10m
     labels:
       env: ENV_LABELS_ENV
       level: critical
-      expr: dm_syncer_binlog_file{node="master"} - ON(instance, task, job) dm_syncer_binlog_file{node="syncer"} > 1
+      expr: (dm_syncer_binlog_file{node="master"} - ON(instance, task, job) dm_syncer_binlog_file{node="syncer"} > 1) and ON(instance, task, job) (dm_worker_task_state == 2)
     annotations:
       description: 'cluster: ENV_LABELS_ENV, instance: {{ $labels.instance }}, task: {{ $labels.task }}, values: {{ $value }}'
       value: '{{ $value }}'

dm/metrics/alertmanager/dm_worker_rules_test.go

@@ -0,0 +1,72 @@
+// Copyright 2026 PingCAP, Inc.
+//
+// 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,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package alertmanager
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"gopkg.in/yaml.v2"
+)
+
+const (
+	binlogFileGapAlertName = "DM_binlog_file_gap_between_master_syncer"
+	binlogFileGapAlertExpr = `(dm_syncer_binlog_file{node="master"} - ON(instance, task, job) dm_syncer_binlog_file{node="syncer"} > 1) and ON(instance, task, job) (dm_worker_task_state == 2)`
+)
+
+type alertRule struct {
+	Alert       string            `yaml:"alert"`
+	Expr        string            `yaml:"expr"`
+	For         string            `yaml:"for"`
+	Labels      map[string]string `yaml:"labels"`
+	Annotations map[string]string `yaml:"annotations"`
+}
+
+type alertRulesFile struct {
+	Groups []struct {
+		Name  string      `yaml:"name"`
+		Rules []alertRule `yaml:"rules"`
+	} `yaml:"groups"`
+}
+
+func TestBinlogFileGapAlertRuleRequiresRunningTask(t *testing.T) {
+	rule := loadAlertRule(t, "dm_worker.rules.yml", binlogFileGapAlertName)
+
+	require.Equal(t, binlogFileGapAlertExpr, rule.Expr)
+	require.Equal(t, binlogFileGapAlertExpr, rule.Labels["expr"])
+	require.Equal(t, "10m", rule.For)
+}
+
+func loadAlertRule(t *testing.T, filename, alertName string) alertRule {
+	t.Helper()
+
+	content, err := os.ReadFile(filename)
+	require.NoError(t, err)
+
+	var ruleFile alertRulesFile
+	require.NoError(t, yaml.Unmarshal(content, &ruleFile))
+
+	for _, group := range ruleFile.Groups {
+		for _, rule := range group.Rules {
+			if rule.Alert == alertName {
+				require.NotEmpty(t, rule.Expr)
+				return rule
+			}
+		}
+	}
+
+	t.Fatalf("alert rule %q not found in %s", alertName, filename)
+	return alertRule{}
+}