MySQL crash-safe replication is an old feature (~4 years as of MySQL 5.6), but it’s not consistently understood or applied. The MySQL manual on the topic, 16.3.2 Handling an Unexpected Halt of a Replication Slave, is correct and authoritative, but unless you grok MySQL replication that page doesn’t make it obvious why crash-safe replication works. Other blog posts explain why, but sometimes add other considerations, making it unclear which settings are necessary and sufficient.

MySQL crash-safe replication is an old feature (~4 years as of MySQL 5.6), but it’s not consistently understood or applied. The MySQL manual on the topic, 16.3.2 Handling an Unexpected Halt of a Replication Slave, is correct and authoritative, but unless you grok MySQL replication that page doesn’t make it obvious why crash-safe replication works. Other blog posts explain why, but sometimes add other considerations, making it unclear which settings are necessary and sufficient. The aim of this blog post is total enlightenment, a full crash-safe-spiritual awakening. Light the censers and let us begin at the beginning…

MySQL crash-safe replication is an old feature (~4 years as of MySQL 5.6), but it’s not consistently understood or applied. The MySQL manual on the topic, 16.3.2 Handling an Unexpected Halt of a Replication Slave, is correct and authoritative, but unless you grok MySQL replication that page doesn’t make it obvious why crash-safe replication works. Other blog posts explain why, but sometimes add other considerations, making it unclear which settings are necessary and sufficient.

A common request is to have replication crash-safe in the sense that the replication progress information always is in sync with what has actually been applied to the database, even in the event of a crash. Although transactions are not lost if the server crashes, it could require some tweaking to bring the slaves up again.

In the latest MySQL 5.6 milestone development release, the replication team has implemented crash-safety for the slave by adding the ability of committing the replication information together with the transaction (see Figure 1). This means that replication information will always be consistent with has been applied to the database, even in the event of a server crash. Also, some fixes were done on the master to ensure that it recovers correctly.

If you're familiar with replication, you know that the replication information is stored in two files: master.info and relay-log.info. …