MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4

15.3.8.2 XA Transaction States

An XA transaction progresses through the following states:

  1. Use XA START to start an XA transaction and put it in the ACTIVE state.

  2. For an ACTIVE XA transaction, issue the SQL statements that make up the transaction, and then issue an XA END statement. XA END puts the transaction in the IDLE state.

  3. For an IDLE XA transaction, you can issue either an XA PREPARE statement or an XA COMMIT ... ONE PHASE statement:

    • XA PREPARE puts the transaction in the PREPARED state. An XA RECOVER statement at this point includes the transaction's xid value in its output, because XA RECOVER lists all XA transactions that are in the PREPARED state.

    • XA COMMIT ... ONE PHASE prepares and commits the transaction. The xid value is not listed by XA RECOVER because the transaction terminates.

  4. For a PREPARED XA transaction, you can issue an XA COMMIT statement to commit and terminate the transaction, or XA ROLLBACK to roll back and terminate the transaction.

Here is a simple XA transaction that inserts a row into a table as part of a global transaction: 

mysql> XA START 'xatest';
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO mytable (i) VALUES(10);
Query OK, 1 row affected (0.04 sec)

mysql> XA END 'xatest';
Query OK, 0 rows affected (0.00 sec)

mysql> XA PREPARE 'xatest';
Query OK, 0 rows affected (0.00 sec)

mysql> XA COMMIT 'xatest';
Query OK, 0 rows affected (0.00 sec)

MySQL 8.4 supports detached XA transactions, enabled by the xa_detach_on_prepare system variable (ON by default). Detached transactions are disconnected from the current session following execution of XA PREPARE (and can be committed or rolled back by another connection). This means that the current session is free to start a new local transaction or XA transaction without having to wait for the prepared XA transaction to be committed or rolled back.

When XA transactions are detached, a connection has no special knowledge of any XA transaction that it has prepared. If the current session tries to commit or roll back a given XA transaction (even one which it prepared) after another connection has already done so, the attempt is rejected with an invalid XID error (ER_XAER_NOTA) since the requested xid no longer exists.

Note

Detached XA transactions cannot use temporary tables.

When detached XA transactions are disabled (xa_detach_on_prepare set to OFF), an XA transaction remains connected until it is committed or rolled back by the originating connection. Disabling detached XA transactions is not recommended for a MySQL server instance used in group replication; see Server Instance Configuration, for more information.

If an XA transaction is in the ACTIVE state, you cannot issue any statements that cause an implicit commit. That would violate the XA contract because you could not roll back the XA transaction. Trying to execute such a statement raises the following error: 

ERROR 1399 (XAE07): XAER_RMFAIL: The command cannot be executed
when global transaction is in the ACTIVE state

Statements to which the preceding remark applies are listed at Section 15.3.3, “Statements That Cause an Implicit Commit”.

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