From: Tomas Vondra <tv@fuzzy.cz>
To: pgsql-performance@postgresql.org
Subject: Re: wal_level=archive gives better performance than minimal - why?
Date: Tue, 17 Jan 2012 01:29:53 +0100
Message-ID: <4F14C101.60607@fuzzy.cz> (raw)
In-Reply-To: <4F14A649.5060501@2ndQuadrant.com>
References: <4F0F6A02.3000403@fuzzy.cz>
<4F14A649.5060501@2ndQuadrant.com>
On 16.1.2012 23:35, Greg Smith wrote:
> On 01/12/2012 06:17 PM, Tomas Vondra wrote:
>> I've run a series fo pgbench benchmarks with the aim to see the effect
>> of moving the WAL logs to a separate drive, and one thing that really
>> surprised me is that the archive log level seems to give much better
>> performance than minimal log level.
>
> How repeatable is this? If you always run minimal first and then
> archive, that might be the actual cause of the difference. In this
> situation I would normally run this 12 times, with this sort of pattern:
>
> minimal
> minimal
> minimal
> archive
> archive
> archive
> minimal
> minimal
> minimal
> archive
> archive
> archive
>
> To make sure the difference wasn't some variation on "gets slower after
> each run". pgbench suffers a lot from problems in that class.
AFAIK it's well repeatable - the primary goal of the benchmark was to
see the benefir of moving the WAL to a separate device (with various WAL
levels and device types - SSD and HDD).
I plan to rerun the whole thing this week with a bit more details logged
to rule out basic configuration mistakes etc.
Each run is completely separate (rebuilt from scratch) and takes about 1
hour to complete. Each pgbench run consists of these steps
1) rebuild the data from scratch
2) 10-minute warmup (read-only run)
3) 20-minute read-only run
4) checkpoint
5) 20-minute read-write run
and the results are very stable.
Tomas
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To: pgsql-performance@postgresql.org
Cc: tv@fuzzy.cz
Subject: Re: wal_level=archive gives better performance than minimal - why?
In-Reply-To: <4F14C101.60607@fuzzy.cz>
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