From: Martin Grotzke <martin.grotzke@googlemail.com>
To: Albe Laurenz <laurenz.albe@wien.gv.at>
Cc: pgsql-performance@postgresql.org
Subject: Re: Several optimization options (config/hardware)
Date: Mon, 07 May 2012 11:37:05 +0200
Message-ID: <4FA797C1.7040603@googlemail.com> (raw)
In-Reply-To: <D960CB61B694CF459DCFB4B0128514C207D5012C@exadv11.host.magwien.gv.at>
References: <4FA13444.4050501@googlemail.com>
<D960CB61B694CF459DCFB4B0128514C207D4FCC1@exadv11.host.magwien.gv.at>
<4FA281C4.6040104@googlemail.com>
<D960CB61B694CF459DCFB4B0128514C207D5012C@exadv11.host.magwien.gv.at>
On 05/04/2012 09:57 AM, Albe Laurenz wrote:
> Martin Grotzke wrote:
>>> You could try different kernel I/O elevators and see if that
>>> improves something.
>>>
>>> I have made good experiences with elevator=deadline and
>>> elevator=noop.
>
>> Ok, great info.
>>
>> I'm not sure at which device to look honestly to check the current
>> configuration.
>>
>> mount/fstab shows the device /dev/mapper/VG01-www for the relevant
>> partition. When I check iostat high utilization is reported for
>> the devices dm-4 and sda (showing nearly the same numbers for util
>> always),
>> so I suspect that dm-4 is mapped on sda.
>
> Use the option -N of "iostat" to see long device names. You can use
> "lvm" to figure out the mapping.
iostat with -N shows VG01-www for dm-4. For lvm/lvdisplay/dmsetup I get
"Permission denied" as I have no root/sudo permissions. I need to check
this with our hosting provider (hopefully we have a call today).
>> This is the current config: $ cat /sys/block/sda/queue/scheduler
>> noop anticipatory deadline [cfq] $ cat
>> /sys/block/dm-4/queue/scheduler none
>
> Do you mean literal "none" or do you mean that the file is empty?
"none" was the output of `cat /sys/block/dm-4/queue/scheduler`.
>> Which of them should be changed? I'll discuss this also with our
>> hosting provider next week, he'll know what has to be done.
>
> I'd just add "elevator=deadline" to the kernel line in
> /etc/grub.conf and reboot. At least if it is a dedicated database
> machine.
>
> But of course you want to change it on the fly first to test - not
> knowing the answer to your question, I would change it in both
> devices if I can.
Ok, makes sense.
Cheers,
Martin
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To: pgsql-performance@postgresql.org
Cc: martin.grotzke@googlemail.com, laurenz.albe@wien.gv.at
Subject: Re: Several optimization options (config/hardware)
In-Reply-To: <4FA797C1.7040603@googlemail.com>
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