PostgreSQL 3.3 on gjournaled fs

[Axel Rau]

Hi,

I'm starting migration of my PostgreSQL tablespaces to gjournaled fs
on 7-stable.
Dedicated box is Opteron with Areca.
Any experiences or hints?
4GB journal provider?

Axel
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[Ivan Voras]

The question is - why do you need gjournal? PostgreSQL (and other decent
databases) does its own journaling (search for WAL), so using it on a
journaled file system doesn't do much.

If you really want it, it won't hurt you. Journal size needs to be
scaled based on your load. If you have constant writes you need a larger
journal. You need it to hold 20*(write_rate in MB/s) megabytes. E.g. if
your array does 100 MB/s, you need a 2000 MB journal. This calculation
is for default gjournal settings.

You could put the journal on another drive or array for best
performance. (Of course, you could skip gjournal and put the WAL on the
other drive).

[Axel Rau]

Am 09.08.2008 um 11:03 schrieb Ivan Voras:

> The question is - why do you need gjournal? PostgreSQL (and other
> decent databases) does its own journaling (search for WAL), so using
> it on a journaled file system doesn't do much.

I want to prevent from fsck on large filesystems after outage.

>
>
> If you really want it, it won't hurt you. Journal size needs to be
> scaled based on your load. If you have constant writes you need a
> larger journal. You need it to hold 20*(write_rate in MB/s)
> megabytes. E.g. if your array does 100 MB/s, you need a 2000 MB
> journal. This calculation is for default gjournal settings.

This is usefull info.

>
>
> You could put the journal on another drive or array for best
> performance. (Of course, you could skip gjournal and put the WAL on
> the other drive).

I have the latter, but intent to put this on gjournal too.

Axel
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