syncer(dm): initialize binlog metrics from checkpoint

dm/syncer/syncer.go

@@ -545,11 +545,28 @@ func (s *Syncer) Init(ctx context.Context) (err error) {
 		metricProxies.Init(s.cfg.MetricsFactory)
 	}
 	s.metricsProxies = metricProxies.CacheForOneTask(s.cfg.Name, s.cfg.WorkerName, s.cfg.SourceID)
+	s.initSyncerBinlogMetrics(s.checkpoint.GlobalPoint())
 
 	s.ddlWorker = NewDDLWorker(&s.tctx.Logger, s)
 	return nil
 }
 
+func (s *Syncer) initSyncerBinlogMetrics(checkpoint binlog.Location) {
+	s.metricsProxies.Metrics.BinlogSyncerPosGauge.Set(float64(checkpoint.Position.Pos))
+
+	index, err := utils.GetFilenameIndex(checkpoint.Position.Name)
+	if err != nil {
+		// An empty binlog filename is expected for a fresh or GTID-only checkpoint.
+		// Use NaN so the unknown file number is not exposed as a valid zero value.
+		s.metricsProxies.Metrics.BinlogSyncerFileGauge.Set(math.NaN())
+		if checkpoint.Position.Name != "" {
+			s.tctx.L().Warn("fail to get index number of checkpoint binlog file", log.ShortError(err))
+		}
+		return
+	}
+	s.metricsProxies.Metrics.BinlogSyncerFileGauge.Set(float64(index))
+}
+
 // buildLowerCaseTableNamesMap build a lower case schema map and lower case table map for all tables
 // Input: map of schema --> list of tables
 // Output: schema names map: lower_case_schema_name --> schema_name

dm/syncer/syncer_metrics_test.go

@@ -0,0 +1,92 @@
+// 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 syncer
+
+import (
+	"math"
+	"testing"
+
+	"github.com/go-mysql-org/go-mysql/mysql"
+	"github.com/pingcap/tiflow/dm/pkg/binlog"
+	"github.com/pingcap/tiflow/dm/pkg/gtid"
+	"github.com/pingcap/tiflow/dm/syncer/metrics"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/testutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestInitSyncerBinlogMetrics(t *testing.T) {
+	gtidSet, err := gtid.ParserGTID(
+		mysql.MySQLFlavor,
+		"3ccc475b-2343-11e7-be21-6c0b84d59f30:1-3",
+	)
+	require.NoError(t, err)
+
+	testCases := []struct {
+		name         string
+		checkpoint   binlog.Location
+		expectedFile float64
+		expectedPos  float64
+	}{
+		{
+			name: "file position checkpoint",
+			checkpoint: binlog.NewLocation(mysql.Position{
+				Name: "binary-log.346652",
+				Pos:  560567,
+			}, nil),
+			expectedFile: 346652,
+			expectedPos:  560567,
+		},
+		{
+			name:         "missing position",
+			checkpoint:   binlog.MustZeroLocation(mysql.MySQLFlavor),
+			expectedFile: math.NaN(),
+			expectedPos:  float64(binlog.MinPosition.Pos),
+		},
+		{
+			name: "GTID-only checkpoint",
+			checkpoint: binlog.NewLocation(
+				mysql.Position{},
+				gtidSet,
+			),
+			expectedFile: math.NaN(),
+			expectedPos:  0,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			fileGauge := prometheus.NewGauge(prometheus.GaugeOpts{Name: "syncer_binlog_file"})
+			posGauge := prometheus.NewGauge(prometheus.GaugeOpts{Name: "syncer_binlog_pos"})
+			s := &Syncer{
+				metricsProxies: &metrics.Proxies{
+					Metrics: &metrics.Metrics{
+						BinlogSyncerFileGauge: fileGauge,
+						BinlogSyncerPosGauge:  posGauge,
+					},
+				},
+			}
+
+			s.initSyncerBinlogMetrics(tc.checkpoint)
+
+			actualFile := testutil.ToFloat64(fileGauge)
+			if math.IsNaN(tc.expectedFile) {
+				require.True(t, math.IsNaN(actualFile))
+			} else {
+				require.Equal(t, tc.expectedFile, actualFile)
+			}
+			require.Equal(t, tc.expectedPos, testutil.ToFloat64(posGauge))
+		})
+	}
+}