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By default, MySQL binary logging and replication is statement-based: MySQL also supports row-based replication: Row-based replication was introduced to provide perfect replication of data that is non-deterministic: It can also have a performance impact. Short SQL queries that affect a lot of rows would require more bandwidth to transmit as row-based replication. For example, if replicated by row, this statement would have to uniquely identify 10, rows; it would be much more efficiently transmitted as statement-based: But difficult to evaluate queries that change relatively little data would be much faster to apply to slaves if the master told them what to change instead of forcing them to repeat the work.
For example, this statement requires a table scan and a hash calculation on every row; slaves could save considerable processor time if the master just told them the outcome of all those calculations using row-based replication: In Mixed Mode replication, most queries are replicated by statement.
But transactions MySQL knows are non-deterministic are replicated by row. To test, SSH to master. We're going to look at the format of a statement-based binary log. Tell master to end the current log file and start a new one. Exit MySQL and take a look at this statement in the binary log, using the log file you learned from show master status. You can see in this statement-based binary log file that replication carries a lot metadata to make sure that the statement works the same on the slave:.
Now SSH to slave. Now we're going to intentionally use a function that is not compatible with statement-based replication. The UUID function creates a universally unique identifier. By definition, the output of the UUID function should be different every time it is run. Note, RAND doesn't have this problem; MySQL logs the random number generator seed to the binary log; using the same seed, the slave generates the same pseudorandom number.
You can see that the details column for the newest row is different between the two servers. They're similar because UUID is built from timestamp and network address, and the statement replicated quickly between servers with similar network characteristics. The master will have started a new binary log file during the service restart, so let's run two interesting transactions.
First, insert another row on the master containing a UUID, to show that row-based replication solves that problem:. The master will have started a new binary log file during the service restart, these two transactions are the only content in the latest log file. Near the top of the file, you'll see the transaction where you inserted the working row with a UUID. You'll also notice that there's no obvious way to figure out what is going on reading the log file, even with the help of mysqlbinlog.
The huge binlog data block which we've reproduced barely a fraction of here contains the information the slave will need to uniquely identify each of the affected rows. In Mixed Mode, MySQL uses statement-based replication for most queries, switching to row-based replication only when statement-based replication would cause an inconsistency or corruption.
It is a compromise between the two replication types we've already explored. Now verify that the new row, as replicated to the slave , has a details column that matches the master:. Meanwhile, the DELETE used the more efficient statement-based replication because it did not contain any non-deterministic warning signs. Mixed Mode uses row-based replication for any transaction that: Review a Statement-Based Binary Log.
Review a Row-Based Binary Log. Configure Mixed Mode Replication. Review a Mixed Mode Binary Log.