ZFS-FreeBSD + postgresql performance

[krad]

It is also generally better to allocate the ram to the db rather than zfs.
This reduces context switches, and the db can cache more intelligently that
the file system. However your mileage with this may vary depending on the
db in question. On a system with such a large memory pool limiting zrc to 8
gb, maybe a good thing to do, especially if you can hook up a large l2arc.

You say also say each jail has its own partition, by this i presume you
mean zfs dataset. You may want to consider having separate pools of each
db/jail, as this would limit spindle contention, but could produce a
complicated system.

If your dbs are doing lots of writes, consider implementing raid 10 on the
pools level as its much faster for writes.

As you have a lots of dbs, and potentially a lot of spindles, you could mix
and match the above ideas depending on the dbs profile. Have say a raidz6
pool for you lower traffic mostly read dbs, a raid 10 pool for your heavy
write dbs, and a dedicated pool for you low latency db


On 24 October 2013 09:20, Ronald Klop <ronald-freebsd8 at klop.yi.org> wrote:

> On Wed, 23 Oct 2013 18:25:45 +0200, Albert Shih <Albert.Shih at obspm.fr>
> wrote:
>
>  Hi
>>
>> I would like to known if someone here have in production a FreeBSD server
>> with postgresql and the FS for the data of postgresql is a ZFS pool.
>>
>> I'm going to buy some server with 96Go of Ram and a jbod of 12 disks (4To
>> each)
>>
>> The purpose is to have everything on this zfs pool (except the system who
>> still on classic raid). So to have
>>
>>     many jail (~20-30) running apache/mysql/etc.
>>     one postgresql server with all data on the zfs.
>>
>> each jail use his own zfs partition. So I can use zfs send/received to
>> have
>> a  mirror of everything in a other server.
>>
>> 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....
>>
>> Regards.
>>
>> JAS
>>
>
> Databases do a lot of sync writes, so it might be good to use a fast ZIL
> device (SSD).
>
> Ronald.
>
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