Re: Disk latency goes up during certaing pediods

Luis, The disk only has the WAL (pg_xlog ) directory. Brett, Here are the
mount options:

/dev/sdb1 on /storage/sdb1 type ext3
(rw,noatime,data=writeback,errors=remount-ro)

BTW The original fs was ext4, now I am trying with ext3, with the exact
same results. No noticeable changes using diferent journal modes.

I also tried disabling the journal altogether, which dramatically reduced
the disk usage, but nevertheless there was this latency spikes.

On Mon, Jul 29, 2013 at 3:01 PM, Brett Stauner <brett(at)mightybs(dot)net> wrote:

> Okay, so it's not happening at the same time of day or anything. What are
> your mount options for the WAL disk?
>
>
> On Mon, Jul 29, 2013 at 12:58 PM, German Becker <german(dot)becker(at)gmail(dot)com>wrote:
>
>>
>> Brett,
>>
>> Yes I'm not impying it is postgres related, perhaps is even a normal
>> thing of ext3 /ext4 filesystem, but, this behavioiur is only notable when
>> using postgres and in particular the wal files, as it is very hard disk
>> intensive, soy maybe somenone has seen this befores. The server only task
>> is the database. It has 4 disks one for the os, one for the wal and the
>> other 2 for data. All disks show different access times. The WAL disk is
>> the only one on which the with constant latency, and in certain ocasions it
>> goes up.
>> Plus the ocasions are absolutely random.
>>
>> On Mon, Jul 29, 2013 at 1:15 PM, Brett Stauner <brett(at)mightybs(dot)net>wrote:
>>
>>> "...like if the disk/filesystem gets slower during one hour or so"
>>>
>>> What about a different scheduled task on the system, not necessarily
>>> Postgres related?
>>>
>>>
>>> On Mon, Jul 29, 2013 at 9:17 AM, German Becker <german(dot)becker(at)gmail(dot)com>wrote:
>>>
>>>> Alvaro,
>>>>
>>>> Thanks for your reply. I believe that the only possibility is autovacum
>>>> activity I will check that. Anyway what puzzles me is that
>>>> the throughput does not increase like i might expect if there where high
>>>> VACUUM activity, only the WAIT TIME and thus the UTILIZATION. Is like if
>>>> the disk/filesystem gets slower during one hour or so...
>>>>
>>>>
>>>> On Fri, Jul 26, 2013 at 5:27 PM, Alvaro Herrera <
>>>> alvherre(at)2ndquadrant(dot)com> wrote:
>>>>
>>>>> German Becker escribió:
>>>>> > Hi list,
>>>>> >
>>>>> > I am running Postgres 9.1 on Ubuntu 12.04. I have a dedicated disk
>>>>> for
>>>>> > pg_xlog, using ext4 filesystem with journaling in writeback mode
>>>>> > During high load times, the disk usage is arround 40%. The IO write
>>>>> time is
>>>>> > constant at about 3ms. On certain occasions roughly once in 15
>>>>> days, the
>>>>> > IO write time goes up to about 10ms. This makes the disk usage go up
>>>>> to
>>>>> > almost 100%, probably saturation, and the INSERTS DELETES UPDATES run
>>>>> > considerable slower than normal.This lasts for about 2 hours and
>>>>> then the
>>>>> > latency goes back to 3ms and everything is normal again.
>>>>> > Has anyone seen this behavior? What could be causing the increase in
>>>>> > latency?
>>>>>
>>>>> Can you correlate these episodes with autovacuum activity? Or perhaps
>>>>> backups are being taken (maybe a new base backup is taken every 15
>>>>> days)?
>>>>>
>>>>> --
>>>>> Álvaro Herrera http://www.2ndQuadrant.com/
>>>>> PostgreSQL Development, 24x7 Support, Training & Services
>>>>>
>>>>
>>>>
>>>
>>
>