Question

I’ve been experimenting with master-master replication between two MySQL servers but with different database names and I’ve come accross a bit of a stumbling block. It appears that although UPDATEs work correctly as expected, INSERTs do not.

While I would say that this is a bug or at least a problem with my setup, it appears that MySQL says that this is a feature (here and here).

If then, as MySQL say, it only works on the default database, then how can this setting have a practical real world purpose?

Am I missing something ?

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For reference the relevant parts in my.cnf. I’ve been testing this by doing inserts and updates from within phpMyAdmin if that makes any difference.

master

log-bin=mysql-bin
binlog_do_db=db1

slave

replicate-rewrite-db=db1->db2
replicate-wild-do-table=db2.table1

Answer 1

Replication-rewrite-db usage is same as other replication options. Not only Replication-rewrite-db works on the default database, but these also: replicate-do-db, replicate-ignore-db, binlog-do-db and binlog-ignore-db. Refer this and this.

There are real world purpose, else MySQL wouldn’t have implemented this option. And it works only on default database because–

The main reason for this “check just the default database” behavior is
that it is difficult from the statement alone to know whether it
should be replicated (for example, if you are using multiple-table
DELETE statements or multiple-table UPDATE statements that act across
multiple databases). It is also faster to check only the default
database rather than all databases if there is no need.

You should also know the replication rules. From here.

I tested phpmyadmin by issuing INSERT, DELETE and UPDATE and noticed(By enabling general_query_log) that it issues INIT DB 'db_name'(‘Init DB’ is logged for the mysql_select_db() API call).

For example:

Init DB sakila
1 Query INSERT INTO `sakila`.`actor_info` (`actor_id`, `first_name`, `last_name`, `film_info`) VALUES ('1235', 'abc', 'efg', NULL)

So ultimately the replication shouldn’t break as phpmyadmin does it correctly by executing USE db before every query.