Re: [PATCHES] O_DIRECT for WAL writes

Takahiro,

> scale| DBsize | open_sync | fsync=false | O_DIRECT only| fsync_direct |
> open_direct
> -----+--------+-----------+--------------+--------------+--------------+
>--------------- 10 | 150MB | 252.6 tps | 263.5(+ 4.3%)| 253.4(+ 0.3%)|
> 253.6(+ 0.4%)| 253.3(+ 0.3%) 100 | 1.5GB | 102.7 tps | 117.8(+14.7%)|
> 147.6(+43.7%)| 148.9(+45.0%)| 150.8(+46.8%) 60runs * pgbench -c 10 -t
> 1000
> on one Pentium4, 1GB mem, 2 ATA disks, Linux 2.6.8

This looks pretty good. I'd like to try it out on some of our tests.
Will get back to you on this, but it looks to me like the O_DIRECT
results are good enough to consider accepting the patch.

What filesystem and mount options did you use for this test?

> - Are both fsync_direct and open_direct necessary?
> MySQL seems to use only O_DIRECT+fsync() combination.

MySQL doesn't support as many operating systems as we do. What OSes and
versions will support O_DIRECT?

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco