Heuristic Recovery with the Transaction Coordinator Log

The transaction coordinator log (tc_log) is used to coordinate transactions that affect multiple XA-capable storage engines. One of the main purposes of this log is in crash recovery.

Modes of Crash Recovery

There are two modes of crash recovery:

• Automatic crash recovery.

• Manual heuristic recovery when is set to some value other than OFF.

Automatic Crash Recovery

Automatic crash recovery occurs during startup when MariaDB needs to recover from a crash and is set to OFF, which is the default value.

Automatic Crash Recovery with the Binary Log-Based Transaction Coordinator Log

If MariaDB needs to perform automatic crash recovery and if the is enabled, then the will contain messages like this:

Automatic Crash Recovery with the Memory-Mapped File-Based Transaction Coordinator Log

If MariaDB needs to perform automatic crash recovery and if the is not enabled, then the will contain messages like this:

Manual Heuristic Recovery

Manual heuristic recovery occurs when is set to some value other than OFF. This might be needed if the server finds prepared transactions during crash recovery that are not in the transaction coordinator log. For example, the might contain an error like this:

When manual heuristic recovery is initiated, MariaDB will ignore information about transactions in the transaction coordinator log during the recovery process. Prepared transactions that are encountered during the recovery process will either be rolled back or committed, depending on the value of --tc-heuristic-recover.

When manual heuristic recovery is initiated, the will contain a message like this:

Manual Heuristic Recovery with the Binary Log-Based Transaction Coordinator Log

If is set to some value other than OFF and if the is enabled, then MariaDB will ignore information about transactions in the during the recovery process. Prepared transactions that are encountered during the recovery process will either be rolled back or committed, depending on the value of --tc-heuristic-recover.

After the recovery process is complete, MariaDB will create a new empty file, so that the old corrupt ones can be ignored.

Manual Heuristic Recovery with the Memory-Mapped File-Based Transaction Coordinator Log

If is set to some value other than OFF and if the is not enabled, then MariaDB will ignore information about transactions in the memory-mapped file defined by the option during the recovery process. Prepared transactions that are encountered during the recovery process will either be rolled back or committed, depending on the value of --tc-heuristic-recover.

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