COMMIT
This statement commits a transaction inside of the TIDB server.
In the absence of a BEGIN or START TRANSACTION statement, the default behavior of TiDB is that every statement will be its own transaction and autocommit. This behavior ensures MySQL compatibility.
Synopsis
- CommitStmt
- CompletionTypeWithinTransaction
CommitStmt ::=
'COMMIT' CompletionTypeWithinTransaction?
CompletionTypeWithinTransaction ::=
'AND' ( 'CHAIN' ( 'NO' 'RELEASE' )? | 'NO' 'CHAIN' ( 'NO'? 'RELEASE' )? )
| 'NO'? 'RELEASE'
Examples
mysql> CREATE TABLE t1 (a int NOT NULL PRIMARY KEY);
Query OK, 0 rows affected (0.12 sec)
mysql> START TRANSACTION;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO t1 VALUES (1);
Query OK, 1 row affected (0.00 sec)
mysql> COMMIT;
Query OK, 0 rows affected (0.01 sec)
MySQL compatibility
- Currently, TiDB does not use Metadata Locking (MDL) to prevent DDL statements from modifying tables used by transactions. If the definition of a table has changed, committing a transaction will result in an
Information schema is changederror. In this event, the transaction is rolled back automatically. - By default, TiDB 3.0.8 and later versions use Pessimistic Locking. When using Optimistic Locking, it is important to consider that a
COMMITstatement might fail because rows have been modified by another transaction. - When Optimistic Locking is enabled,
UNIQUEandPRIMARY KEYconstraint checks are deferred until statement commit. This results in additional situations where a aCOMMITstatement might fail. This behavior can be changed by settingtidb_constraint_check_in_place=TRUE. - TiDB parses but ignores the syntax
ROLLBACK AND [NO] RELEASE. This functionality is used in MySQL to disconnect the client session immediately after committing the transaction. In TiDB, it is recommended to instead use themysql_close()functionality of your client driver. - TiDB parses but ignores the syntax
ROLLBACK AND [NO] CHAIN. This functionality is used in MySQL to immediately start a new transaction with the same isolation level while the current transaction is being committed. In TiDB, it is recommended to instead start a new transaction.