mysqlnd_ms_xa_begin

설명

Starts a XA transaction among MySQL servers. PECL/mysqlnd_ms acts as a transaction coordinator the distributed transaction.

Once a global transaction has been started, the plugin injects appropriate XA BEGIN SQL statements on all MySQL servers used in the following. The global transaction is either ended by calling mysqlnd_ms_xa_commit(), mysqlnd_ms_xa_rollback() or by an implicit rollback in case of an error.

During a global transaction, the plugin tracks all server switches, for example, when switching from one MySQL shard to another MySQL shard. Immediately before a query is run on a server that has not been participating in the global transaction yet, XA BEGIN is executed on the server. From a users perspective the injection happens during a call to a query execution function such as mysqli_query(). Should the injection fail an error is reported to the caller of the query execution function. The failing server does not become a participant in the global transaction. The user may retry executing a query on the server and hereby retry injecting XA BEGIN, abort the global transaction because not all required servers can participate, or ignore and continue the global without the failed server.

Reasons to fail executing XA BEGIN include but are not limited to a server being unreachable or the server having an open, concurrent XA transaction using the same xid.

Please note, global and local transactions are mutually exclusive. You cannot start a XA transaction when you have a local transaction open. The local transaction must be ended first. The plugin tries to detect this conflict as early as possible. It monitors API calls for controlling local transactions to learn about the current state. However, if using SQL statements for local transactions such as BEGIN, the plugin may not know the current state and the conflict is not detected before XA BEGIN is injected and executed.

The use of other XA resources but MySQL servers is not supported by the function. To carry out a global transaction among, for example, a MySQL server and another vendors database system, you should issue the systems SQL commands yourself.

Note: Experimental

The feature is currently under development. There may be issues and/or feature limitations. Do not use in production environments.