Remove unused code for old START_GTID logic (vitessio#17265)

Signed-off-by: Dirkjan Bussink <d.bussink@gmail.com>

go/vt/vttablet/tabletserver/tx_pool.go

@@ -40,9 +40,8 @@ import (
 )
 
 const (
-	txLogInterval  = 1 * time.Minute
-	beginWithCSRO  = "start transaction with consistent snapshot, read only"
-	trackGtidQuery = "set session session_track_gtids = START_GTID"
+	txLogInterval = 1 * time.Minute
+	beginWithCSRO = "start transaction with consistent snapshot, read only"
 )
 
 var txIsolations = map[querypb.ExecuteOptions_TransactionIsolation]string{
@@ -394,16 +393,6 @@ func createStartTxStmt(options *querypb.ExecuteOptions, readOnly bool) (string,
 }
 
 func handleConsistentSnapshotCase(ctx context.Context, conn *StatefulConnection) (beginSQL string, sessionStateChanges string, err error) {
-	_, err = conn.execWithRetry(ctx, trackGtidQuery, 1, false)
-	// We allow this to fail since this is a custom MySQL extension, but we return
-	// then if this query was executed or not.
-	//
-	// Callers also can know because the sessionStateChanges will be empty for a snapshot
-	// transaction and get GTID information in another (less efficient) way.
-	if err == nil {
-		beginSQL = trackGtidQuery + "; "
-	}
-
 	isolationLevel := txIsolations[querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY]
 
 	execSQL, err := setIsolationLevel(ctx, conn, isolationLevel)

go/vt/vttablet/tabletserver/tx_pool_test.go

@@ -701,11 +701,11 @@ func TestTxPoolBeginStatements(t *testing.T) {
 		expBeginSQL:      "set transaction isolation level serializable; start transaction read only",
 	}, {
 		txIsolationLevel: querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY,
-		expBeginSQL:      "set session session_track_gtids = START_GTID; set transaction isolation level repeatable read; start transaction with consistent snapshot, read only",
+		expBeginSQL:      "set transaction isolation level repeatable read; start transaction with consistent snapshot, read only",
 	}, {
 		txIsolationLevel: querypb.ExecuteOptions_CONSISTENT_SNAPSHOT_READ_ONLY,
 		readOnly:         true,
-		expBeginSQL:      "set session session_track_gtids = START_GTID; set transaction isolation level repeatable read; start transaction with consistent snapshot, read only",
+		expBeginSQL:      "set transaction isolation level repeatable read; start transaction with consistent snapshot, read only",
 	}, {
 		txIsolationLevel: querypb.ExecuteOptions_AUTOCOMMIT,
 		expBeginSQL:      "",

go/vt/vttablet/tabletserver/vstreamer/snapshot_conn.go

@@ -132,29 +132,6 @@ func (conn *snapshotConn) startSnapshot(ctx context.Context, table string) (gtid
 	return replication.EncodePosition(mpos), nil
 }
 
-// startSnapshotWithConsistentGTID performs the snapshotting without locking tables. This assumes
-// session_track_gtids = START_GTID, which is a contribution to MySQL and is not in vanilla MySQL at the
-// time of this writing.
-func (conn *snapshotConn) startSnapshotWithConsistentGTID(ctx context.Context) (gtid string, err error) {
-	if _, err := conn.ExecuteFetch("set transaction isolation level repeatable read", 1, false); err != nil {
-		return "", err
-	}
-	result, err := conn.ExecuteFetch("start transaction with consistent snapshot, read only", 1, false)
-	if err != nil {
-		return "", err
-	}
-	// The "session_track_gtids = START_GTID" patch is only applicable to MySQL56 GTID, which is
-	// why we hardcode the position as mysql.Mysql56FlavorID
-	mpos, err := replication.ParsePosition(replication.Mysql56FlavorID, result.SessionStateChanges)
-	if err != nil {
-		return "", err
-	}
-	if _, err := conn.ExecuteFetch("set @@session.time_zone = '+00:00'", 1, false); err != nil {
-		return "", err
-	}
-	return replication.EncodePosition(mpos), nil
-}
-
 // Close rolls back any open transactions and closes the connection.
 func (conn *snapshotConn) Close() {
 	_, _ = conn.ExecuteFetch("rollback", 1, false)