Galera Cluster High Ping

Question

I have 3 gameservers connected at the same database. I started using galera cluster to sync, because mysql remote connection gets a delay because of hosts distance, BR, US and FR, and my gameserver use only one main thread for important queries.

This delay (lag) happen because principal thread need receive callback (confirmation) before continue running the aplication.

I thought thatwithn galera cluster, using local database with ping 0 the problem doesnt will happen anymore, but I don't know why, everytime that I get INSERTS and DELET on database the same lag happens. On my application debug, I see that queries are sent local with 0 MS but it still lagging.

My question is, does galera mysql-wsrep needs confirmation of other clusters?

Answer 1

Galera checks with all the other nodes during the COMMIT command. This is when the lag occurs. Of course, COMMIT is explicitly or implicitly (autocommit) part of any transaction, so every transaction has that lag.

This implies that the optimal use of a geographically-dispersed Galera Cluster is to put many actions in a single transaction. (On the other hand, too many things in a single transaction can lead to undoing too much if there is any failure/deadlock/etc.)

The lag between US and Europe is on the order of 100ms; is that what you are seeing?