With statement-based replication, triggers executed on the master also execute on the slave. With row-based replication, triggers executed on the master do not execute on the slave. Instead, the row changes on the master resulting from trigger execution are replicated and applied on the slave.
This behavior is by design. If under row-based replication the slave applied the triggers as well as the row changes caused by them, the changes would in effect be applied twice on the slave, leading to different data on the master and the slave.
If you want triggers to execute on both the master and the slave—perhaps because you have different triggers on the master and slave—you must use statement-based replication. However, to enable slave-side triggers, it is not necessary to use statement-based replication exclusively. It is sufficient to switch to statement-based replication only for those statements where you want this effect, and to use row-based replication the rest of the time.
Before MySQL 5.1.31, a trigger that was defined on a transactional table but that updated a nontransactional table could cause updates on the transactional table to be replicated before they were actually committed on the master, and not be rolled back correctly on the slave if they were rolled back on the master. (Bug #40116) See also Section 22.214.171.124, “Replication and Transactions”.
A statement invoking a trigger (or function) that causes an
update to an
AUTO_INCREMENT column is not
replicated correctly using statement-based replication.
Beginning with MySQL 5.1.40, such statements are marked as
unsafe. (Bug #45677)