Re: Oracle Linux IO Tunning - filesystemio_options- disk_asynch_io - PAGECACHE - aio-max-size - O_DIRECT

From: Chris Marquez <marquezemail_at_gmail.com>
Date: 2005-12-20 03:17:04
Message-id: d494e9760512191817h411ec0a2pd7e183e2c6625182@mail.gmail.com

Answered some of my own questions...more RIF. ;o)

>>but *why* is asynch-IO not the default

This note explains it all...I think I have been confusing and expecting what I got from UNIX world in the Linux world.

Doc ID:     Note:225751.1
Subject:     Asynchronous I/O (aio) on RedHat Advanced Server
Type:     FAQ
Creation Date:     13-JAN-2003
Last Revision Date:     20-OCT-2004

Frequently Asked Questions (FAQ) Asynchronous I/O (aio) on RedHat Advanced Server Version 2.1 - 3.0

>>OS directio mounts

http://www.redhat.com/magazine/013nov05/features/oracle/ I am really confused it this is even available for Linux "mount" options. I see reference to Solaris and "forcedirectio" option but not Linux? This doc seems to indicate it is possible, but no specifics?

Chris Marquez
Oracle DBA

On 12/19/05, Chris Marquez wrote:
>
>
> ENV:
> Oracle 9205 -on- RHEL3 -on- EXT3
>
> All,
>
> I have been reading previous post, my own notes and some info on the
> internet.
> I'm primarily interested in Oracle and using
> "filesystemio_options=asynch", but
> feel all/many of these OS parameters / options are related, but not
> required?
>
> I would like any and all opinions on these (below), but again I'm 99% sure
> I'm going with "filesystemio_options=asynch" ASAP.
>
>
> ---Oracle
> =========
> - filesystemio_options=asynch|directio|setall|none
> =========
> 1.) I know when, since 9iR2 and 10g...but *why* is asynch-IO not the
> default with Oracle RDBMS anymore?
> Wasn't it a monumental moment when in Oracle7?, Oracle Corp. made
> available Oracle RDBMS asynch-IO?...what we all wanted and
>
> needed? I was a little surprised and caught off guard to find I had to
> re-implement and learn this stuff again?
>
> I have a poor memory, but keep good notes...it seems I did implement this
> on my 9iRAC-RHEL3-OCFS system, but promptly un-did
>
> it after obvious problems...it was recommended we use asynch-IO with OCFS.
> :o| Again for this thread I'm on *EXT3* now.
>
>
> =========
> - disk_asynch_io=TRUE
> =========
> 2.) I guess this is obvious...if I use filesystemio_options=asynch, would
> leave the default "disk_asynch_io=TRUE" setting.
>
>
>
> ---OS/Linux
> =========
> - PAGECACHE
> =========
> 3.) Never used it. These seems to controls my/the OS IO cache that Oracle
> filesystemio_options=asynch would use?
> I have the OS default and scared to make changes with know the true
> impact.
>
> [oracle_at_db08 bdump]$ more /proc/sys/vm/pagecache
> 1 15 100
>
> max=100(%)...I think I like knowing that OS will not "move process pages
> to swap"?
>
> http://www.redhat.com/magazine/001nov04/features/vm/
> pagecache
> The pagecache file adjusts the amount of RAM which can be used by the page
> cache.
>
>
>
> =========
> - aio-max-size
> =========
> 4.) Never used it. This seems like good info...I have 2 OLTP db's and 1
> OLAP db.
> Anyone have experience with these (when using Oracle asynch I/O)?
>
> http://www.puschitz.com/TuningLinuxForOracle.shtml
>
> Increasing I/O Throughput at the Linux OS Level
>
> The /proc/sys/fs/aio-max-size parameter can be changed if asynchronous I/O
>
> is used for Oracle datafiles residing on filesystems (e.g. "ext2").
> ...
> For Online Transaction Processing (OLTP) workloads, the default size of
> 131072 would suffice.
>
>
> =========
> - O_DIRECT
> =========
> 5.) This seems obvious and only at the OS level...this is covered (in
> Oracle) by the filesystemio_options parameter.
>
>
> I await your input...Thanks!
>
> --
> Chris Marquez
> Oracle DBA

--
Chris Marquez
Oracle DBA

Received on Tue Dec 20 2005 - 03:17:04 CST