On MySQL-5.7.2, we released a new type of multi-threaded slave (MTS). It is called logical clock based MTS. Because it can parallel apply transactions in the same schema, it has the potential to improve slave throughput on almost any application, regardless of the schema layout. After it was released, we continued to work on the framework to improve it further. Therefore, 5.7.5 includes a few enhancements, in addition to those released as part of previous DMRs. This blog post introduces one of the new features in the latest DMR.

slave_preserve_commit_order

It is a system global variable and can be set dynamically.

• SET GLOBAL slave_perserve_commit_order = {ON|OFF};

Enabling this variable ensures that the order which transactions were committed on the master is preserved on the slave. The replication threads must be stopped before enabling this variable and this variable only affects logical clock based …

 I am happy to announce that slave_transaction_retries is available on multi-threaded slave now. You will no longer see the warning that slave_transaction_retries is not supported by multi-threaded slave since MySQL-5.7.5.

Multi-threaded slave and single-threaded slave share the system variable slave_transaction_retries and they have similar transaction retry logic. So this blog just brings you a little new knowledge and then refresh you with the transaction retry logic.

Transaction Retry In Worker Threads

For multi-threaded slave, Transaction retry is done in worker threads when they are applying their transactions. When a worker thread encounters a temporary error, it needs to read the transaction’s events from relay log by itself and then apply them again.

The only new thing is that worker threads need to read events from relay log by themselves. To support it, coordinator stores relay log position of …