8.15. Making Online Schema Changes
Similar to the maintenance procedure, schema changes to an underlying
dataserver may need to be performed on dataservers that are not part of an
active dataservice. Although many inline schema changes, such as the
addition, removal or modification of an existing table definition will be
correctly replicated to slaves, other operations, such as creating new
indexes, or migrating table data between table definitions, is best
performed individually on each dataserver while it has been temporarily
taken out of the dataservice.
If you are attempting an Online schema change and running in a MSMM
environment, then you should follow the steps in
Performing Schema Changes.
The basic process is to temporarily put each slave offline, perform the
schema update, and then put the slave online and monitor it and catch up.
Operations supported by these online schema changes must be backwards
compatible. Changes to the schema on slaves that would otherwise break the
replication cannot be performed using the online method.
The following method assumes a schema update on the entire dataservice by
modifying the schema on the slaves first. The schema shows three
datasources being updated in sequence, slaves first, then the master.
With any schema change to a database, the database performance should be
monitored to ensure that the change is not affecting the overall