Galera

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Galera disk bound workload revisited

Update 2012-01-09: I have now been able to understand the poor(ish) results in this benchmark. They are very likely due to a bad hardware setup and neither Galera nor InnoDB is to blame. See http://openlife.cc/blogs/2012/january/re-doing-galera-disk-bound-benchmark

People commenting on my results for benchmarking Galera on a disk bound workload seemed to be confused by the performance degrading when writing to more than one master, and not convinced at my speculations on the reasons. Since sysbench 0.5 has the benchmarks in the form of LUA scripts, it was temptingly easy to tweak those a little to see if my speculations were correct. So yesterday I did run tests again with a slightly modified sysbench workload. (Everything else is identical, so see previous article for details on the setup.)

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More Galera lessons: parallel slave, out of order commits and deadlocks

2 concepts I've been an active advocate of during the past few years are both supported by Galera: Multi-threaded (aka parallel) slave, and allowing out-of-order commits on such a parallel slave. In trying to optimize Galera settings for the disk bound workload I just reported on, I also came to test these alternatives.

Single threaded vs Multi threaded slave

All of my previously reported tests have been run with wsrep_slave_threads=32. For the memory-bound workload there was no difference using one thread or more, but I left it at 32 "just in case". For the disk bound workload there is a clear benefit in having a multi-threaded slave:

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Benchmarking Galera on a disk bound workload

Update 2012-01-09: I have now been able to understand the poor(ish) results in this benchmark. They are very likely due to a bad hardware setup and neither Galera nor InnoDB is to blame. See http://openlife.cc/blogs/2012/january/re-doing-galera-disk-bound-benchmark

After getting very good results with Galera with using a memory bound workload, I was eager to then also test a disk bound workload. Also this time I learned a lot about how Galera behaves and will try to share those findings here.

Setup

The setup for these tests is exactly the same as in last weeks benchmarks, except that I've now loaded the database with 10 tables containing 40 million rows each. This sums up to about 90GB database:

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Running sysbench tests against a Galera cluster

So, vacation is over and I was in luck: Already during first week I had ample time to finally put Galera replication to the test. It was a great experience: I learned a lot, and eventually got the great results I was hoping to see.

Again I've started by just running the standard Sysbench oltp read-write test. Since this is a commonly used benchmark, it produces numbers that are comparable with others running the same benchmarks. Including, as it happens, Galera developers themselves.

These tests were run on an 8 core server with 32 GB of RAM and the disk on some EMC device with a 2,5GB write cache.

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The ultimate MySQL high availability solution

A while ago Baron blogged about his utter dislike for MMM, a framework supposedly used as a MySQL high-availability solution. While I have no personal experience with this framework, reading the comments to that blog I'm indeed convinced that Baron is right. For one thing, it includes the creator of MMM agreeing.

Baron's post still suggests - and having spoken with him I know that's what he has in mind - that a better solution could be built, it's just MMM that has a poor design. I'm going to go further than that: Personally, I've come to think that this family of so called clustering suites is just categorically the wrong approach to database high-availability. I will now explain why they fail, and what the right way is instead.

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First touch: Galera clustering for MySQL

I've been following the Galera project for years now, but this week I finally had some time to spend hands on time on it. I'm sure you noticed Vadim from Percona is also looking at it, it will be interesting to compare results. In this post I will just share the experience of installing and configuring Galera.

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