pmysql (multi-server mysql client)

To have more visibility of our systems I needed a method to quickly query large sets of MySQL servers. Though there are few methods like ‘xargs -P’ and dsh, they are overkill for the SQL-only job, and simply not fast enough.

So, I hacked pmysql (274 lines of C) – a tool that is able to run queries on multiple servers in parallel. It can run SQL query on 1000 servers in under 0.1s, and scales well with larger sets of servers.

Use cases can be various – from configuration/schema checks (I really enjoyed using information_schema), to ‘global processlist’ analysis.
Ability to crunch hundreds of megabytes of processlist info in few seconds – priceless, so is schema verification of millions of tables.

It is fast enough to use it as backend for some of real-time health check CGI scripts :-)

To get the source:
bzr co lp:mysqlatfacebook/tools/pmysql

P.S. Oh, I know that nearly nobody needs it, but thats not a reason for keeping it closed :)

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.