mysql(ticdc): remove returned error and modify the log in `CheckIsTiD…

…B ` (#11506)

close #11505

cdc/sink/ddlsink/mysql/mysql_ddl_sink.go

@@ -91,10 +91,7 @@ func NewDDLSink(
 		return nil, err
 	}
 
-	cfg.IsTiDB, err = pmysql.CheckIsTiDB(ctx, db)
-	if err != nil {
-		return nil, err
-	}
+	cfg.IsTiDB = pmysql.CheckIsTiDB(ctx, db)
 
 	cfg.IsWriteSourceExisted, err = pmysql.CheckIfBDRModeIsSupported(ctx, db)
 	if err != nil {

cdc/sink/dmlsink/txn/mysql/mysql.go

@@ -107,10 +107,7 @@ func NewMySQLBackends(
 		return nil, err
 	}
 
-	cfg.IsTiDB, err = pmysql.CheckIsTiDB(ctx, db)
-	if err != nil {
-		return nil, err
-	}
+	cfg.IsTiDB = pmysql.CheckIsTiDB(ctx, db)
 
 	cfg.IsWriteSourceExisted, err = pmysql.CheckIfBDRModeIsSupported(ctx, db)
 	if err != nil {

cdc/syncpointstore/mysql_syncpoint_store.go

@@ -64,10 +64,7 @@ func newMySQLSyncPointStore(
 		return nil, err
 	}
 
-	cfg.IsTiDB, err = pmysql.CheckIsTiDB(ctx, syncDB)
-	if err != nil {
-		return nil, err
-	}
+	cfg.IsTiDB = pmysql.CheckIsTiDB(ctx, syncDB)
 
 	cfg.IsWriteSourceExisted, err = pmysql.CheckIfBDRModeIsSupported(ctx, syncDB)
 	if err != nil {

pkg/sink/mysql/db_helper.go

@@ -263,16 +263,16 @@ func GenBasicDSN(sinkURI *url.URL, cfg *Config) (*dmysql.Config, error) {
 
 // CheckIfBDRModeIsSupported checks if the downstream supports BDR mode.
 func CheckIfBDRModeIsSupported(ctx context.Context, db *sql.DB) (bool, error) {
-	isTiDB, err := CheckIsTiDB(ctx, db)
-	if err != nil || !isTiDB {
-		return false, err
+	isTiDB := CheckIsTiDB(ctx, db)
+	if !isTiDB {
+		return false, nil
 	}
 	testSourceID := 1
 	// downstream is TiDB, set system variables.
 	// We should always try to set this variable, and ignore the error if
 	// downstream does not support this variable, it is by design.
 	query := fmt.Sprintf("SET SESSION %s = %d", "tidb_cdc_write_source", testSourceID)
-	_, err = db.ExecContext(ctx, query)
+	_, err := db.ExecContext(ctx, query)
 	if err != nil {
 		if mysqlErr, ok := errors.Cause(err).(*dmysql.MySQLError); ok &&
 			mysqlErr.Number == tmysql.ErrUnknownSystemVariable {
@@ -284,16 +284,30 @@ func CheckIfBDRModeIsSupported(ctx context.Context, db *sql.DB) (bool, error) {
 }
 
 // CheckIsTiDB checks if the downstream is TiDB.
-func CheckIsTiDB(ctx context.Context, db *sql.DB) (bool, error) {
+func CheckIsTiDB(ctx context.Context, db *sql.DB) bool {
 	var tidbVer string
 	// check if downstream is TiDB
 	row := db.QueryRowContext(ctx, "select tidb_version()")
 	err := row.Scan(&tidbVer)
 	if err != nil {
-		log.Error("check tidb version error", zap.Error(err))
-		return false, nil
-	}
-	return true, nil
+		log.Warn("check tidb version error, the downstream db is not tidb?", zap.Error(err))
+		// In earlier versions, this function returned an `error` along with a boolean value,
+		// which allowed callers to differentiate between network-related issues and
+		// the absence of TiDB. However, since the specific error content wasn't critical to
+		// the logic—external callers only needed to know whether the downstream was TiDB—the
+		// decision was made to simplify the function. External callers should not handle the
+		// error returned here because even if the downstream is not TiDB, TiCDC should still
+		// function properly, for more details: https://github.com/pingcap/tiflow/pull/11214
+		//
+		// So instead of returning an `error`, we now log a warning if the
+		// query fails. This keeps the external interface clean while still
+		// providing observability into network or query issues through logs.
+		//
+		// Note: The function returns `false` and logs a warning if the
+		// query to retrieve the TiDB version fails.
+		return false
+	}
+	return true
 }
 
 // QueryMaxPreparedStmtCount gets the value of max_prepared_stmt_count

pkg/sink/observer/observer.go

@@ -92,10 +92,7 @@ func NewObserver(
 		db.SetMaxIdleConns(2)
 		db.SetMaxOpenConns(2)
 
-		isTiDB, err := pmysql.CheckIsTiDB(ctx, db)
-		if err != nil {
-			return nil, err
-		}
+		isTiDB := pmysql.CheckIsTiDB(ctx, db)
 		if isTiDB {
 			return NewTiDBObserver(db), nil
 		}