IDS Forum

RE: Informix I/O performance

Posted By: Art S. Kagel
Date: Tuesday, 23 June 2009, at 7:44 a.m.

In Response To: Informix I/O performance (KAMRAN HAQ)

On my phone so the quoting is not good. Introducing my comments with 'ASK'=
. See below:

Art=20
-----Original Message-----
From: KAMRAN HAQ <khaq@i2cinc.com>
Sent: Tuesday, June 23, 2009 5:24 AM
To: ids@iiug.org
Subject: Informix I/O performance [16129]

Informix version: Informix 11.5FC4=20
Operating system: SunOS 5.10 sun4v sparc (64bit)=20
SAN: ENC connecrted through HBA=20
Raid level: 10=20
File System: Ext3=20

We 've neither using raw-devices nor configured the KAIO.=20
And running about 12 databases of OLTP nature, having a couple of big table=
s=20
with lot of indexes on them.=20
We need to know that for OLTP databases with frequent read & writes what of=
=20
the followings would be better to use and what are hazards:=20
1- KAIO (also the guidlines for change in existing number of AIO VPs)=20

ASK - KAIO is enabled by default, but, you need to enable DIRECT_IO for it =
to work for COOKED filesystem chunks. RAW is better? But not by much (5%).=
If you enable DIRECT_IO then either start with 4 AIO VPs and tune or star=
t with 2 and turn on AUTO_AIO and let the engine tune them for you.

2- Journaling (disabling it is recommended on this forum for performance ga=
in,=20
but it is said that enabling it makes the system more safe)=20

ASK- NO JOURNALED FILESYSTEMS! You should not be using EXT3 even. Perform=
ance isn't as good as a non-joournaled FS and IDS does its own logging whic=
h is far safer than the journaling anyway. IDS's writes are all either und=
er O_SYNC or O_DIRECT to pre-allocated disk space so the journaling gains y=
ou nothing and costs you speed. Also some journaled FSs are unsafe - EXT3 =
with writeback enable and EXT4 always are two such. See the web on the iss=
ues.

Second question is about temp dbspace; how can we distribute more than one=
=20
temp dbspaces, and other dbspaces to reduce I/O contention as their are=20
several databases running on same machine and using same SAN.=20

ASK - Get the database off the shared SAN! Is ounds trite but it is the ON=
LY solution. Database and filesystems have VERY different access patterns.=
Trying to share a database's storage with other apps is a bad idea and a=
dding multiple machines to the mix is deadly. I don't care what the SAN ve=
ndors say on this one.

regards,=20
Kamran=20

***************************************************************************=
****=20
Forum Note: Use "Reply" to post a response in the discussion forum.=20

Messages In This Thread

• Informix I/O performance
  KAMRAN HAQ -- Tuesday, 23 June 2009, at 5:24 a.m.
  • RE: Informix I/O performance
    Art S. Kagel -- Tuesday, 23 June 2009, at 7:44 a.m.

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