Jonas, > > Hi Noah > > I'm not sure where you have your information from, but it's wrong. I do not > even know what Galera is, nor do I have 3 servers.
Then you should go research Galera http://codership.com/content/using-galera-cluster and http://www.percona.com/software/percona-xtradb-cluster because it's has "mostly-true" synchronous replication for MySQL. In this mode, you are "semi-garuanteed" that your write has been completed on all servers. > MySQL master-master replication have worked fine out of the box at least > since 5.x Yes, there is a replication mode in MySQL that allows for a two-server Master/Master configuration. However it's NOT synchronous. Therefore you have no guarantee that the write has happened on the other server. There are other HA configurations for MySQL: Master/Slave with asynchronous replication, and Master/Slave with DRBD, but they both have their own issues. That being said, you either have replication lag with a two server MySQL setup, or you can have lock contention in Galera if you're hitting the same table, which is probably what would happen with Baruwa. > > The reason why you need more than 1 master is to be able to still write to > the DB when the primary master goes down, as it would in a normal standalone > setup or master-slave setup. With a plethora of HA setups, you can automatically switch your slave to master to be able to write within a very small window (transparent to the end client). Especially with PostgreSQL synchronous replication, when you can be assured that your DB will stay consistent and up to date during a failure scenario. Most applications (including Baruwa, since it uses SQLAlchemy) should have no problem reconnecting to your DB layer after a failure scenario. I'm not sure why you think that a 30-60 second failover scenario would not be appropriate for an application like Baruwa? I would always prefer 30-60 seconds of failover time and DB consistency. > > Not to mention its better performance to write on many, and on top of that > introducing anything with a failover is a risk in itself, since you never > know if it works when you need it. Here your information is just plainly incorrect. There is not "better performance" by writing to many. First of all you can lose consistency very quickly. Secondly, you're doubling your writes on each server in a two-server scenario. > With true master-master replication you know everything works, because you > use both masters everyday, unlike a passive/cold/slave server. This again is where you are incorrect. I urge you to look into consulting from experts in this field, such as: http://www.hastexo.com and http://www.percona.com > Hope that explains it :) You're not explaining anything. And you're giving incorrect information to the list. Thanks. ~Noah _______________________________________________ http://pledgie.com/campaigns/12056
