MySQL 5.0 Reference Manual  /  ...  /  Replication and Transactions Replication and Transactions

Mixing transactional and nontransactional statements within the same transaction. In general, you should avoid transactions that update both transactional and nontransactional tables in a replication environment. You should also avoid using any statement that accesses both transactional and nontransactional tables and writes to any of them.

In MySQL 5.0 the server uses this rule for binary logging: If the initial statements in a transaction are nontransactional, they are written to the binary log immediately. The remaining statements in the transaction are cached and not written to the binary log until the transaction is committed. (If the transaction is rolled back, the cached statements are written to the binary log only if they make nontransactional changes that cannot be rolled back. Otherwise, they are discarded.)

To apply this rule, the server considers a statement nontransactional if the first changes it makes change nontransactional tables, transactional if the first changes it makes change transactional tables. First applies in the sense that a statement may have several effects if it involves such things as triggers, stored functions, or multiple-table updates.

In situations where transactions mix updates to transactional and nontransactional tables, the order of statements in the binary log is correct, and all needed statements are written to the binary log even in case of a ROLLBACK. However, when a second connection updates the nontransactional table before the first connection transaction is complete, statements can be logged out of order because the second connection update is written immediately after it is performed, regardless of the state of the transaction being performed by the first connection.

Using different storage engines on master and slave. It is possible to replicate transactional tables on the master using nontransactional tables on the slave. For example, you can replicate an InnoDB master table as a MyISAM slave table. However, if you do this, there are problems if the slave is stopped in the middle of a BEGIN ... COMMIT block because the slave restarts at the beginning of the BEGIN block.

When the storage engine type of the slave is nontransactional, transactions on the master that mix updates of transactional and nontransactional tables should be avoided because they can cause inconsistency of the data between the master transactional table and the slave nontransactional table. That is, such transactions can lead to master storage engine-specific behavior with the possible effect of replication going out of synchrony. MySQL does not issue a warning about this currently, so extra care should be taken when replicating transactional tables from the master to nontransactional tables on the slaves.

Beginning with MySQL 5.0.56, every transaction (including autocommit transactions) is recorded in the binary log as though it starts with a BEGIN statement, and ends with either a COMMIT or a ROLLBACK statement. However, this does not apply to nontransactional changes; any statements affecting tables using a nontransactional storage engine such as MyISAM are regarded for this purpose as nontransactional, even when autocommit is enabled. (Bug #26395)

Download this Manual
User Comments
Sign Up Login You must be logged in to post a comment.