INSERT speed, paramy, auto-inc

One of first things I noticed, when I tried to run some 5.0 tests, was that INSERT speed was much slower (no benchmarking at that time, purely subjective speed that loading the dump was somewhat too slow).

After discussing at evening, and some coding in the morning I built paramy – a simple C++ utility, that reads .sql stream, and spreads execution of statements over multiple worker threads.

For benchmarking I took a simple 13m row, 1.6G data, 1.7G index table. Loading it with standard mysql client took 30min (7200r/s). Paramy unfortunately hit auto-inc lock, and didn’t provide too much of performance – data load took 25min (8700r/s). The win here was mostly because everything until InnoDB being parallel, as instead of 100% core use, mysqld went up to ~130%, so it obviously managed to get additional cycles from SMP.

Dropping AUTO-INC from the field description changed everything. Standard mysql load wasn’t much faster, but under paramy load mysqld managed to use ~320% of CPU core, and did the load in 10min (~21500r/s).

The interesting part – no INSERT asks for AUTO-INC values, so in theory one can just disable the locking during the load, and re-enable it same way as unique or foreign key constraint checks are re-enabled after import of data – that way loading of data into InnoDB would be much much faster, especially with many more cores – though then contention moves away to transaction log mutex.

Additional way to reduce contention inside InnoDB may be removing both reading and writing checksums- they have quite big CPU load share. Disabling this at least during bulk imports can be quite useful.

Oh, I mentioned the subjective feeling that 5.0 was slower. I finally benchmarked – 4.0 did the data load in five minutes, and went over 40000 rows/s. I hope this is the last test where 4.0 is twice faster than 5.0.

Trainwreck: external MySQL replication agent

I wanted to work more on the actual project before writing about it, but I’m lazy, and dear community may be not.

At Wikimedia we have one database server which replicates from multiple (like 15!) masters. It even splits replication streams by database, and applying changes in parallel.

All this stuff is done by external replication agent, Trainwreck. It is public-domain software, which was written by River, doesn’t have much documentation, works only on Solaris (River likes Solaris), unless you comment out all process management blocks, which use doors and other Solaris specific API.

It lives in Wikimedia SVN, and can be checked out using:

svn co

It sits there, maintained just for needs of that specific single server (ok, there might be two or three), so if anyone wants to make it available for broader audience, feel free to fork a project to some community-oriented place, add all nice features you need. :)