Re: WAL in RAM

Marcus Engene <mengpg2@engene.se> wrote:

> Every now and then I have write peaks which causes annoying delay
> on my website

> Does anyone here have any recommendations here?

For our largest machines we put WAL on a RAID1 drive pair dedicated
to that task, on its own controller with battery-backed cache
configured for write-back.  It does make a big difference, because
when a DBA accidentally got this wrong once, we saw the problem you
describe, and moving WAL to the dedicated drives/controller caused
the problem to go away.

If problems remain, look for posts by Greg Smith on how to tune
this.  You may want to extend your checkpoint completion target,
make the background writer more aggressive, reduce shared buffers,
or tune the OS.  But if you can afford to put WAL on a dedicated
file system something like the above, that would be a better place
to start, IMO.

-Kevin