Mysqlnd_ms Functions
PHP Manual

mysqlnd_ms_xa_gc

Garbage collects unfinished XA transactions after severe errors

Description

int mysqlnd_ms_xa_gc ( mixed $connection [, string $gtrid [, boolean $ignore_max_retries ]] )

Garbage collects unfinished XA transactions.

The XA protocol is a blocking protocol. There exist cases when servers participating in a global transaction cannot make progress when the transaction coordinator crashes or disconnects. In such a case, the MySQL servers keep waiting for instructions to finish the XA transaction in question. Because transactions occupy resources, transactions should always be terminated properly.

Garbage collection requires configuring a state store to track global transactions. Should a PHP client crash in the middle of a transaction and a new PHP client be started, then the built-in garbage collection can learn about the aborted global transaction and terminate it. If you do not configure a state store, the garbage collection cannot perform any cleanup tasks.

The state store should be crash-safe and be highly available to survive its own crash. Currently, only MySQL is supported as a state store.

Garbage collection can also be performed automatically in the background. See the plugin configuration directive garbage_collection for details.

Note: Experimental

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

Parameters

connection

A MySQL connection handle obtained from any of the connect functions of the mysqli, mysql or PDO_MYSQL extensions.

gtrid

Global transaction identifier (gtrid). If given, the garbage collection considers the transaction only. Otherwise, the state store is scanned for any unfinished transaction.

ignore_max_retries

Whether to ignore the plugin configuration max_retries setting. If garbage collection continuously fails and the max_retries limit is reached prior to finishing the failed global transaction, you can attempt further runs prior to investigating the cause and solving the issue manually by issuing appropriate SQL statements on the participants. Setting the parameter has the same effect as temporarily setting max_retries = 0.

Return Values

Returns TRUE if garbage collection was successful. Otherwise, returns FALSE