16.3.3 Using Replication with Different Source and Replica Storage Engines
It does not matter for the replication process whether the source table on the source and the replicated table on the replica use different engine types. In fact, the
storage_engine system variables are not replicated.
This provides a number of benefits in the replication process in that you can take advantage of different engine types for different replication scenarios. For example, in a typical scale-out scenario (see Section 16.3.4, “Using Replication for Scale-Out”), you want to use
InnoDB tables on the source to take advantage of the transactional functionality, but use
MyISAM on the replicas where transaction support is not required because the data is only read. When using replication in a data-logging environment you may want to use the
Archive storage engine on the replica.
Configuring different engines on the source and replica depends on how you set up the initial replication process:
If you used mysqldump to create the database snapshot on your source, you could edit the dump file text to change the engine type used on each table.
Another alternative for mysqldump is to disable engine types that you do not want to use on the replica before using the dump to build the data on the replica. For example, you can add the
--skip-federatedoption on your replica to disable the
FEDERATEDengine. If a specific engine does not exist for a table to be created, MySQL will use the default engine type, usually
MyISAM. (This requires that the
NO_ENGINE_SUBSTITUTIONSQL mode is not enabled.) If you want to disable additional engines in this way, you may want to consider building a special binary to be used on the replica that only supports the engines you want.
If you are using raw data files (a binary backup) to set up the replica, you will be unable to change the initial table format. Instead, use
ALTER TABLEto change the table types after the replica has been started.
For new source/replica replication setups where there are currently no tables on the source, avoid specifying the engine type when creating new tables.
If you are already running a replication solution and want to convert your existing tables to another engine type, follow these steps:
Stop the replica from running replication updates:
mysql> STOP SLAVE;
This will enable you to change engine types without interruptions.
ALTER TABLE ... ENGINE='for each table to be changed.
Start the replication process again:
mysql> START SLAVE;
default_storage_engine variable is not replicated, be aware that
CREATE TABLE and
ALTER TABLE statements that include the engine specification will be correctly replicated to the replica. For example, if you have a CSV table and you execute:
mysql> ALTER TABLE csvtable Engine='MyISAM';
The above statement will be replicated to the replica and the engine type on the replica will be converted to
MyISAM, even if you have previously changed the table type on the replica to an engine other than CSV. If you want to retain engine differences on the source and replica, you should be careful to use the
default_storage_engine variable on the source when creating a new table. For example, instead of:
mysql> CREATE TABLE tablea (columna int) Engine=MyISAM;
Use this format:
mysql> SET default_storage_engine=MyISAM; mysql> CREATE TABLE tablea (columna int);