I confess I am a Galera fanboy. This post is going to present two slogans about Galera reminding you about Galera “limitations”. This is for the sake of user experience:)
- One Cluster
Think about Galera as One Cluster. As every transaction is committed virtually synchronously, the slowest node determines the (DML) speed of the cluster. This is true regarding the network too.
Galera is still some kind of replication. So keep in mind to provide PK as for (ROW based) Replication. There is a Featurerequest of mine to have a PK option to enforce creating of Tables with a PK. Please vote for it:)
With traditional MySQL Replication the slave might lag. This is not hurting the performance of the master. With Galera there is no lag. So if applying takes time it stalls the cluster (flow control). DDL statements run in Total Order Isolation (TOI) as a default. This will not only block the table. The whole cluster stalls till the DDL finishes.
Of course there is much more to tell. This two slogans are just a result of my experience with customers etc.