Re: ZFS-FreeBSD + postgresql performance

> I would also recommend to use 4K sector size using
gnop and zpool export/import.

Agree, in my small setup, 4K sectors and aligned partition can be seven or eight times faster than 512kb sectors when the harddisk is in advance format (4kb per sectors)

Also suggest to have two separte fast SSD (in mirror mode) for the ZIL.
This is to avoid ZFS file system fragmentation when the ZIL is stored intent with the ZFS.

Patrick

On Thursday, October 24, 2013 10:18 PM, "Ivailo(dot)TANUSHEFF(at)raiffeisen(dot)bg" <Ivailo(dot)TANUSHEFF(at)raiffeisen(dot)bg> wrote:

owner-freebsd-fs(at)freebsd(dot)org wrote on 23.10.2013 23:57:57:

> From:
>
> Michael Schmiedgen <schmiedgen(at)gmx(dot)net>
>
> To:
>
> Mark Felder <feld(at)FreeBSD(dot)org>, Albert Shih <Albert(dot)Shih(at)obspm(dot)fr>,
> pgsql-admin(at)postgresql(dot)org, freebsd-fs(at)freebsd(dot)org, freebsd-jail(at)freebsd(dot)org,
>
> Date:
>
> 23.10.2013 23:58
>
> Subject:
>
> Re: ZFS-FreeBSD + postgresql performance
>
> Sent by:
>
> owner-freebsd-fs(at)freebsd(dot)org
>
> On 10/23/13 19:14, Mark Felder wrote:
> > On Wed, Oct 23, 2013, at 11:25, Albert Shih wrote:
> >> My question is about the performance, I known ZFS eat all
memory he can
> >> have (or almost), so what append when we run database like
postgresql and
> >> jail ? (it's also the reason of 96 Go ram).
> >>
> >> Sorry for cross-posting but it's about 3 differents things....
> >>
> >
> > To my understanding the solution is to change the primarycache
to
> > "metadata" for any ZFS filesystem that you do not want
ZFS to heavily
> > cache in memory.
> >
> > Example:
> >
> > # zfs set primarycache=metadata tank/usr/local/pgsql
>
> In addition to this it is recommended to set the recordsize
> to the fixed value of 8k on dataset creation.
>
> Michael
>

I would also recommend to use 4K sector size using
gnop and zpool export/import.
I agree that using fixed recordsize is a must when
you have databases and you have DB on each jail.
Also there are a bunch of sysctl parameters you may
want to play with, mostly about tuning the memory usage.

Also it might be an idea to use partitions on disks
and:
1. Use first 1-2G on each disk for swap (just in case).
2. Use the rest of the disk for 4K aligned and 4K
sector size partition, labelled in some way (I use disk ID as label, for
easy identification).

Best regards,
Ivailo Tanusheff

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