Re: Several optimization options (config/hardware)

From: Albe Laurenz
Subject: Re: Several optimization options (config/hardware)
Date: ,
Msg-id: D960CB61B694CF459DCFB4B0128514C207D5012C@exadv11.host.magwien.gv.at
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In response to: Re: Several optimization options (config/hardware)  (Martin Grotzke)
Responses: Re: Several optimization options (config/hardware)  (Martin Grotzke)
List: pgsql-performance

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Several optimization options (config/hardware)  (Martin Grotzke, )
 Re: Several optimization options (config/hardware)  ("Tomas Vondra", )
 Re: Several optimization options (config/hardware)  ("Albe Laurenz", )
  Re: Several optimization options (config/hardware)  (Martin Grotzke, )
   Re: Several optimization options (config/hardware)  ("Albe Laurenz", )
    Re: Several optimization options (config/hardware)  (Martin Grotzke, )

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.

> 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?

> 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.

Yours,
Laurenz Albe


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