Global transaction IDs
PECL/mysqlnd_ms can do client-side transparent global transaction ID injection. In its most basic form, a global transaction identifier is a counter which is incremented for every transaction executed on the master. The counter is held in a table on the master. Slaves replicate the counter table. In case of a master failure a database administrator can easily identify the most recent slave for promiting it as a new master. The most recent slave has the highest transaction identifier. Application developers can ask the plugin for the global transaction identifier (GTID) for their last successful write operation. The plugin will return an identifier that refers to an transaction no older than that of the clients last write operation. Then, the GTID can be passed as a parameter to the quality of service (QoS) filter as an option for session consistency. Session consistency ensures read your writes. The filter ensures that all reads are either directed to a master or a slave which has replicated the write referenced by the GTID. When injection is done The plugin transparently maintains the GTID table on the master. In autocommit mode the plugin injects an UPDATE statement before executing the users statement for every master use. In manual transaction mode, the injection is done before the application calls commit() to close a transaction. The configuration option report_error of the GTID section in the plugins configuration file is used to control whether a failed injection shall abort the current operation or be ignored silently (default). Please note, the PHP version requirements for transaction boundary monitoring and their limits. Limitations Client-side global transaction ID injection has shortcomings. The potential issues are not specific to PECL/mysqlnd_ms but are rather of general nature.
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