From: Scott Carey <scott@richrelevance.com>
To: ml@bortal.de <ml@bortal.de>
To: Greg Smith <gsmith@gregsmith.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Postgres benchmarking with pgbench
Date: Thu, 19 Mar 2009 14:59:10 -0700
Message-ID: <C5E80E3E.3886%scott@richrelevance.com> (raw)
In-Reply-To: <49C2B854.4080303@bortal.de>
On 3/19/09 2:25 PM, "ml@bortal.de" <ml@bortal.de> wrote:
>
> Here is my config (maybe with some odd setting):
> http://pastebin.com/m5d7f5717
>
> I played around with:
> - max_connections
> - shared_buffers
> - work_mem
> - maintenance_work_mem
> - checkpoint_segments
> - effective_cache_size
>
> ..but whatever i do, the graph looks the same. Any hints or tips what my
> config should look like? Or are these results even okay? Maybe i am
> driving myself crazy for nothing?
>
> Cheers,
> Mario
>
I'm assuming this is linux: What linux version? What is your kernel's
dirty_ratio and background_dirty_ratio?
The default for a long time was 40 and 10, respectively. This is far too
large for most uses on today's servers, you would not want 40% of your RAM
to have pages not yet flushed to disk except perhaps on a small workstation.
See
Current kernels default to 10 and 5, which is better.
What is best for your real life workload will differ from pg_bench here.
I don't know if this is the cause for any of your problems, but it is
related closely to the checkpoint_segments and checkpoint size/time
configuration.
Is your xlog on the same device as the data? I have found that for most
real world workloads, having the xlog on a separate device helps
tremendously. Even more so for 'poor' RAID controllers like the PERC5 --
your sync writes in xlog will be interfering with the RAID controller cache
of your data due to bad design.
But my pg_bench knowledge with respect to this is limited.
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To: pgsql-performance@postgresql.org
Cc: scott@richrelevance.com, ml@bortal.de, gsmith@gregsmith.com
Subject: Re: Postgres benchmarking with pgbench
In-Reply-To: <C5E80E3E.3886%scott@richrelevance.com>
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