Thread: symlinking pg_xlog

symlinking pg_xlog

From
KÖPFERL Robert
Date:
Hi,

due to I/O-bottle necks I think of making a symlink from pg_xlog to another
physical disk.
This is a modification inside the cluster dir. What kind of idea is that?
bad one?

Re: symlinking pg_xlog

From
Michael Fuhr
Date:
On Fri, Jun 24, 2005 at 03:18:12PM +0200, KÖPFERL Robert wrote:
>
> due to I/O-bottle necks I think of making a symlink from pg_xlog to another
> physical disk.
> This is a modification inside the cluster dir. What kind of idea is that?
> bad one?

See the "Write-Ahead Logging (WAL)" chapter in the documentation:

http://www.postgresql.org/docs/8.0/static/wal-internals.html

"It is of advantage if the log is located on another disk than the
main database files.  This may be achieved by moving the directory
pg_xlog to another location (while the server is shut down, of
course) and creating a symbolic link from the original location in
the main data directory to the new location."

Several third-party performance-tuning documents make the same
recommendation.

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/

Re: symlinking pg_xlog

From
Tom Lane
Date:
=?iso-8859-1?Q?K=D6PFERL_Robert?= <robert.koepferl@sonorys.at> writes:
> due to I/O-bottle necks I think of making a symlink from pg_xlog to another
> physical disk.
> This is a modification inside the cluster dir. What kind of idea is that?
> bad one?

That's exactly the recommended way to put xlog on a separate disk.

Don't forget to shut down the postmaster while moving xlog around ;-)

            regards, tom lane

Re: symlinking pg_xlog

From
"Jason Minion"
Date:
Go for it, it's suggested:

http://www.postgresql.org/docs/8.0/interactive/wal-internals.html

Jason Minion
IT Developer
Sigler Printing & Publishing
413 Northwestern Ave
Ames, IA 50010
515-232-6997
jason.minion@sigler.com


-----Original Message-----
From: pgsql-admin-owner@postgresql.org
[mailto:pgsql-admin-owner@postgresql.org]On Behalf Of KÖPFERL Robert
Sent: Friday, June 24, 2005 8:18 AM
To: [ADMIN]
Subject: [ADMIN] symlinking pg_xlog


Hi,

due to I/O-bottle necks I think of making a symlink from pg_xlog to another
physical disk.
This is a modification inside the cluster dir. What kind of idea is that?
bad one?

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Re: symlinking pg_xlog

From
Tim.Shenton@corp.terralycos.com
Date:
Last week I was testing PG under different RAID configurations and I moved
pg_xlog to other drives and set up the symlink in the data directory
(pg_xlog -> /home/test/pg-log).  PG worked fine and there were no problems

Tim

----------------------
Timothy Shenton
Lycos, Inc.
(781) 370-2876


|---------+-------------------------------->
|         |           Michael Fuhr         |
|         |           <mike@fuhr.org>      |
|         |           Sent by:             |
|         |           pgsql-admin-owner@pos|
|         |           tgresql.org          |
|         |                                |
|         |                                |
|         |           06/24/2005 09:40 AM  |
|         |                                |
|---------+-------------------------------->
  >----------------------------------------------------------------------------------------------------------|
  |                                                                                                          |
  |        To:      KÖPFERL Robert <robert.koepferl@sonorys.at>                                              |
  |        cc:      "[ADMIN]" <pgsql-admin@postgresql.org>                                                   |
  |        Subject: Re: [ADMIN] symlinking pg_xlog                                                           |
  >----------------------------------------------------------------------------------------------------------|




On Fri, Jun 24, 2005 at 03:18:12PM +0200, KÖPFERL Robert wrote:
>
> due to I/O-bottle necks I think of making a symlink from pg_xlog to
another
> physical disk.
> This is a modification inside the cluster dir. What kind of idea is that?
> bad one?

See the "Write-Ahead Logging (WAL)" chapter in the documentation:

http://www.postgresql.org/docs/8.0/static/wal-internals.html

"It is of advantage if the log is located on another disk than the
main database files.  This may be achieved by moving the directory
pg_xlog to another location (while the server is shut down, of
course) and creating a symbolic link from the original location in
the main data directory to the new location."

Several third-party performance-tuning documents make the same
recommendation.

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/

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    (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)






Re: symlinking pg_xlog

From
KÖPFERL Robert
Date:
Thanks to all of you.

I actually read the chapter but I just remembered to not touch pg's own area
pg_*
So ...  I'll go for it

|-----Original Message-----
|From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
|Sent: Freitag, 24. Juni 2005 15:50
|To: KÖPFERL Robert
|Cc: [ADMIN]
|Subject: Re: [ADMIN] symlinking pg_xlog
|
|
|=?iso-8859-1?Q?K=D6PFERL_Robert?= <robert.koepferl@sonorys.at> writes:
|> due to I/O-bottle necks I think of making a symlink from
|pg_xlog to another
|> physical disk.
|> This is a modification inside the cluster dir. What kind of
|idea is that?
|> bad one?
|
|That's exactly the recommended way to put xlog on a separate disk.
|
|Don't forget to shut down the postmaster while moving xlog around ;-)
|
|            regards, tom lane
|