Chapter 19 Replication

Table of Contents     [+/-]

19.1 Chapter Organization

19.2 Source Code Files

19.3 Principles     [+/-]

19.3.1 Binlog Formats

19.3.2 Differences Between Master and Slave

19.3.3 Crashes

19.3.4 Binlog Files and Indexes

19.4 Rules     [+/-]

19.4.1 Determining the Logging Format

19.4.2 Unsafe Statements

19.4.3 Logging Transactions

19.4.4 Logging Updates to auto_increment Columns

19.4.5 Logging Access to Variables and Functions

19.4.6 Other Unsafe Statements

19.4.7 binlog_row_image

19.4.8 Replication Locks

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.