WSREP Binlog Transaction Coordinator

The commit ordering between the binary log and storage engines should be consistent. This is done by implementing the TC_LOG interface functions (particularly log_and_order). The MYSQL_BIN_LOG class implements these functions to decide this commit ordering. This however, creates a problem for servers running with Galera. This is because Galera also decides its own commit ordering independently from the TC_LOG logic. In other words, when a server is configured with both the binary log and Galera enabled, both components try to decide their own commit ordering separately.

For consistency in such setups, Galera should implement TC_LOG::log_and_order to force the binary log ordering to be consistent with its own ordering.