Working as MySQL DBA, you will often have to deal with schema changes. Changes to production databases are not popular among DBAs, but they are necessary when applications add new requirements on the databases. If you manage a Galera Cluster, this is even more challenging than usual - the default method of doing schema changes (Total Order Isolation) locks the whole cluster for the duration of the alter. There are two more ways to go, though - online schema change and Rolling Schema Upgrade.
A popular method of performing schema changes, using pt-online-schema-change, has its own limitations. It can be tricky if your workload consists of long running transactions, or the workload is highly concurrent and the …[Read more]