Re: Massive I/O spikes during checkpoint

On Jul 9, 2012, at 10:51 PM, Maxim Boguk wrote:

>
>
> But what appears to be happening is that all of the data is being written out at the end of the checkpoint.
>
> This happens at every checkpoint while the system is under load.
>
> I get the feeling that this isn't the correct behavior and i've done something wrong.
>
>
>
> It's not an actual checkpoints.
> It's is a fsync after checkpoint which create write spikes hurting server.
> You should set sysctl vm.dirty_background_bytes and vm.dirty_bytes to reasonable low values

So use bla_bytes instead of bla_ratio?

> (for 512MB raid controller with cache I would suggest to sometning like
> vm.dirty_background_bytes = 33554432
> vm.dirty_bytes = 268435456
> 32MB and 256MB respectively)

I'll take a look.

>
> If youre server doesn't have raid with BBU cache - then you should tune these values to much lower values.
>
> Please read http://blog.2ndquadrant.com/tuning_linux_for_low_postgresq/
> and related posts.

yeah, I saw that I guess I didn't put 2+2 together. thanks.