Обсуждение: Neat trick

I figured out how to speed up the sequential scans using "blockdev"
command. Essentially, this increases the read-ahead on the underlying
block device for the file system. It will change the read-ahead value
for the entire disk, even if there are several partitions on the disk.
The results are very promising. Unfortunately, I didn't take baseline
numbers and measure the effect with precision, but the look of it is
that things are much faster with the read-ahead set to 2048 instead of
the default 256. The read-ahead is measured in sectors read ahead by the
OS. The OS is Red Hat Linux, EL 5.5.

--

Mladen Gogala
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
http://www.vmsinfo.com
The Leader in Integrated Media Intelligence Solutions

blockdev is a Linux utility for examining block devices (such as
/dev/sda) and for configuring certain aspects of how I/O is performed
on those devices.  See http://man.he.net/man8/blockdev.

Will

On 15 September 2010 15:33, Arvind Sharma <arvind321@yahoo.com> wrote:
> Hi Mladen,
>
> Which attribute in the postgresql.conf file this is set ?
>
> I am running CentOS Linux, PG 8.4
>
> Thanks!
> Arvind
>
>
> ________________________________
> From: Mladen Gogala <mgogala@vmsinfo.com>
> To: "pgsql-novice@postgresql.org" <pgsql-novice@postgresql.org>
> Sent: Tue, September 14, 2010 2:30:28 PM
> Subject: [NOVICE] Neat trick
>
> I figured out how to speed up the sequential scans using "blockdev" command.
> Essentially, this increases the read-ahead on the underlying block device
> for the file system. It will change the read-ahead value for the entire
> disk, even if there are several partitions on the disk.  The results are
> very promising. Unfortunately, I didn't take baseline numbers and measure
> the effect with precision, but the look of it is that things are much faster
> with the read-ahead set to 2048 instead of the default 256. The read-ahead
> is measured in sectors read ahead by the OS. The OS is Red Hat Linux, EL
> 5.5.
>
> --
> Mladen Gogala Sr. Oracle DBA
> 1500 Broadway
> New York, NY 10036
> (212) 329-5251
> http://www.vmsinfo.com The Leader in Integrated Media Intelligence Solutions
>
>
>
>
> -- Sent via pgsql-novice mailing list (pgsql-novice@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-novice
>
>

Arvind, this is not a postgresql.conf, this is an OS trick. Your linux
has "blockdev" command.

Arvind Sharma wrote:
> Hi Mladen,
>
> Which attribute in the postgresql.conf file this is set ?
>
> I am running CentOS Linux, PG 8.4
>
> Thanks!
> Arvind
>
>
> ------------------------------------------------------------------------
> *From:* Mladen Gogala <mgogala@vmsinfo.com>
> *To:* "pgsql-novice@postgresql.org" <pgsql-novice@postgresql.org>
> *Sent:* Tue, September 14, 2010 2:30:28 PM
> *Subject:* [NOVICE] Neat trick
>
> I figured out how to speed up the sequential scans using "blockdev"
> command. Essentially, this increases the read-ahead on the underlying
> block device for the file system. It will change the read-ahead value
> for the entire disk, even if there are several partitions on the
> disk.  The results are very promising. Unfortunately, I didn't take
> baseline numbers and measure the effect with precision, but the look
> of it is that things are much faster with the read-ahead set to 2048
> instead of the default 256. The read-ahead is measured in sectors read
> ahead by the OS. The OS is Red Hat Linux, EL 5.5.
>
> --
> Mladen Gogala Sr. Oracle DBA
> 1500 Broadway
> New York, NY 10036
> (212) 329-5251
> http://www.vmsinfo.com The Leader in Integrated Media Intelligence
> Solutions
>
>
>
>
> -- Sent via pgsql-novice mailing list (pgsql-novice@postgresql.org
> <mailto:pgsql-novice@postgresql.org>)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-novice
>


--

Mladen Gogala
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
http://www.vmsinfo.com
The Leader in Integrated Media Intelligence Solutions