Date: Wed, 1 Apr 2015 23:19:38 -0300 (ART)
From: Gerardo Herzig <gherzig@fmed.uba.ar>
To: Pietro Pugni <pietro.pugni@gmail.com>
Cc: pgsql-performance@postgresql.org
Message-ID: <87131335.225702.1427941178942.JavaMail.root@fmed.uba.ar>
In-Reply-To: <732B95A3-FEC8-4623-9AC5-98FD30F00863@gmail.com>
Subject: Re: Can't get Dell PE T420 (Perc H710) perform better
 than a MacMini with PostgreSQL
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Ok, a quick view on the system, and some things that may be important to note:

> Our deployment machine is a Dell PowerEdge T420 with a Perc H710 RAID
> controller configured in this way:
> 
>     * VD0: two 15k SAS disks (ext4, OS partition, WAL partition,
>     RAID1)
>     * VD1: ten 10k SAS disks (XFS, Postgres data partition, RAID5)
> 

Well...usually RAID5 have the worst performance in writing...EVER!!! Have you tested this in another raid configuration? RAID10 is usually the best bet.

> 
> 
> This system has the following configuration:
> 
>     * Ubuntu 14.04.2 LTS (GNU/Linux 3.13.0-48-generic x86_64)
>     * 128GB RAM (DDR3, 8x16GB @1600Mhz)
>     * two Intel Xeon E5-2640 v2 @2Ghz
>     * Dell Perc H710 with 512MB RAM (Write cache: "WriteBack", Read
>     cache: "ReadAhead", Disk cache: "disabled"):
>         * VD0 (OS and WAL partition): two 15k SAS disks (ext4, RAID1)
>         * VD1 (Postgres data partition): ten 10k SAS disks (XFS,
>         RAID5)
>     * PostgreSQL 9.4 (updated to the latest available version)
>     * moved pg_stat_tmp to RAM disk
> 
> 
[...]> versions.
> 
You did not mention any "postgres" configuration at all. If you let the default checkpoint_segments=3, that would be an IO hell for your disk controler...and the RAID5 making things worst...Can you show us the values of:

checkpoint_segments
shared_buffers
work_mem
maintenance_work_mem
effective_io_concurrency

I would start from there, few changes, and check again. I would change the RAID first of all things, and try those tests again.

Cheers.
Gerardo


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