From: Bob Lunney <bob_lunney@yahoo.com>
To: Havasvölgyi Ottó <havasvolgyi.otto@gmail.com>
To: Marti Raudsepp <marti@juffo.org>
Cc: Aidan Van Dyk <aidan@highrise.ca>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Response time increases over time
Date: Thu, 8 Dec 2011 07:58:30 -0800 (PST)
Message-ID: <1323359910.29568.YahooMailNeo@web39703.mail.mud.yahoo.com> (raw)
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Otto,
Separate the pg_xlog directory onto its own filesystem and retry your tests.
Bob Lunney
________________________________
From: Havasvölgyi Ottó <havasvolgyi.otto@gmail.com>
To: Marti Raudsepp <marti@juffo.org>
Cc: Aidan Van Dyk <aidan@highrise.ca>; pgsql-performance@postgresql.org
Sent: Thursday, December 8, 2011 9:48 AM
Subject: Re: [PERFORM] Response time increases over time
I have moved the data directory (xlog, base, global, and everything) to an ext4 file system. The result hasn't changed unfortuately. With the same load test the average response time: 80ms; from 40ms to 120 ms everything occurs.
This ext4 has default settings in fstab.
Have you got any other idea what is going on here?
Thanks,
Otto
2011/12/8 Marti Raudsepp <marti@juffo.org>
On Thu, Dec 8, 2011 at 06:37, Aidan Van Dyk <aidan@highrise.ca> wrote:
>> Let me guess, debian squeeze, with data and xlog on both on a single
>> ext3 filesystem, and the fsync done by your commit (xlog) is flushing
>> all the dirty data of the entire filesystem (including PG data writes)
>> out before it can return...
>
>This is fixed with the data=writeback mount option, right?
>(If it's the root file system, you need to add
>rootfsflags=data=writeback to your kernel boot flags)
>
>While this setting is safe and recommended for PostgreSQL and other
>transactional databases, it can cause garbage to appear in recently
>written files after a crash/power loss -- for applications that don't
>correctly fsync data to disk.
>
>Regards,
>Marti
>
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Subject: Re: Response time increases over time
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