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Chapter 19 Replication

Status of this section: up to date 2009-10-21

This chapter describes MySQL replication principles, rules, and code, as it is supposed to work in version 5.1.

The MySQL replication feature allows a server - the master - to send all changes to another server - the slave - and the slave tries to apply all changes to keep up-to-date with the master. Replication works as follows:

  • Whenever the master's database is modified, the change is written to a file, the so-called binary log, or binlog. This is done by the client thread that executed the query that modified the database.

  • The master has a thread, called the dump thread, that continuously reads the master's binlog and sends it to the slave.

  • The slave has a thread, called the IO thread, that receives the binlog that the master's dump thread sent, and writes it to a file: the relay log.

  • The slave has another thread, called the SQL thread, that continuously reads the relay log and applies the changes to the slave server.