From: Greg Smith <greg@2ndquadrant.com>
To: Jon Schewe <jpschewe@mtu.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: How filesystems matter with PostgreSQL
Date: Sat, 05 Jun 2010 18:52:55 -0400
Message-ID: <4C0AD547.2040308@2ndquadrant.com> (raw)
In-Reply-To: <4C0AD280.5020105@mtu.net>
References: <4C08EEDF.7090403@mtu.net>
<4C0AD180.90607@2ndquadrant.com>
<4C0AD280.5020105@mtu.net>
Jon Schewe wrote:
>> If that's the case, what you've measured is which filesystems are
>> safe because they default to flushing drive cache (the ones that take
>> around 15 minutes) and which do not (the ones that take >=around 2
>> hours). You can't make ext3 flush the cache correctly no matter what
>> you do with barriers, they just don't work on ext3 the way PostgreSQL
>> needs them to.
>>
>>
> So the 15 minute runs are doing it correctly and safely, but the slow
> ones are doing the wrong thing? That would imply that ext3 is the safe
> one. But your last statement suggests that ext3 is doing the wrong thing.
>
I goofed and reversed the two times when writing that. As is always the
case with this sort of thing, the unsafe runs are the fast ones. ext3
does not ever do the right thing no matter how you configure it, you
have to compensate for its limitations with correct hardware setup to
make database writes reliable.
--
Greg Smith 2ndQuadrant US Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com www.2ndQuadrant.us
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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, jpschewe@mtu.net
Subject: Re: How filesystems matter with PostgreSQL
In-Reply-To: <4C0AD547.2040308@2ndquadrant.com>
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