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Comment by SoftwareMaven | Hacker News Reader

The answer to that is simple, even with the little information given: Flikr used MySQL, the CTO driving the changes at Etsy came from Flikr, therefore, Etsy now uses Flikr.

Given their existing investment in Postgresql, I can't imagine they suddenly had more experience internally with MySQL, though the CTO may have been the only person with any horizontal DB scaling experience since Etsy didn't scale before.

I've seen the pattern of "CTO changes tech to something he/she is familiar with" many times. Sometimes that's good; mostly, it annoys the teams who are now less efficient. We certainly don't have enough info here to know. The scaling argument (his knowledge thereof, not Postgresql's "inability") is pretty compelling.

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If you read the comments that preceded yours in responding to my question, you'll see that there are perfectly apolitical reasons for them to have done this move; they wanted a scale-out less DBA-controlled database, and at the time there wasn't a built-in Postgres way to do that.

Also, knowing how to scale DB X and not knowing how to scale DB Y often means scaling DB Y is a science project.

I feel bad for baiting people into psychoanalyzing Etsy's team.

There still isn't a built-in way in postgres to do master-master replication.

Neither is master-master built into MySQL.

You can apparently do that with Galera, but I haven't seen that in production.

What they're referring to is most likely MySQL's half-baked "circular replication". Some people claim it works for them. Personally I tried it once and the usual MySQL replication issues (desync, InnoDB deadlock) would create much more uncomfortable situations than in a Master/Slave setup.

With master/slave you at least stand a chance of having one half of the pair survive through a problem. With circular replication the cluster would lock up hard almost every time for us, and - to add insult to injury - leave the pair inconsistent after recovery.

Whatever your opinion of MySQL's replication, the MySQL community calls it master-master.

I think the confusion here is based on the difference between "multi-master" replication and "master-master" replication. MySQL doesn't support the former, where a machine can be a slave of more than one master, but it does support (like you eluded to) having two masters (usually one writable, one read-only) in a loop, which MySQL folks call "master-master" replication.

http://postgres-xc.sourceforge.net/ does not count?

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