RE: Low FD limit a performance issue?
- From: "Chitale, Hemant Krishnarao" <Hemant.Chitale@xxxxxx>
- To: <Dave.Herring@xxxxxxxxxx>
- Date: Fri, 4 Nov 2011 09:48:11 +0800
Oracle Support article
Open Files/Open File Descriptors [ID 787780.1]
explains the difference between file-descriptors and open files
Hemant K Chitale
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Herring Dave - dherri
Sent: Friday, November 04, 2011 1:48 AM
To: Kurt
Cc: oracle-l List
Subject: RE: Low FD limit a performance issue?
Currently the base is 1024 and we're working with ASM, so in the end we'd only
have to worry if somehow a database process needed to open more than 1024
non-ASM database files, which I can't imagine how that'd ever be the case in
our environment. Maybe this only applies to non-ASM dbs.
DAVID HERRING
DBA
Acxiom Corporation
EML dave.herring@xxxxxxxxxx
TEL 630.944.4762
MBL 630.430.5988
1501 Opus Pl, Downers Grove, IL 60515, USA
WWW.ACXIOM.COM<http://www.acxiom.com/>
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From: Kurt [mailto:kurtengelo@xxxxxxxxx]
Sent: Wednesday, November 02, 2011 6:32 PM
To: Herring Dave - dherri
Cc: oracle-l List
Subject: Re: Low FD limit a performance issue?
Hi Dave,
I didn't have time to actually test this - so take it for what it's worth.
I believe what happens if you don't have a sufficient FD limit is that when the
Oracle database hits the number of open files, it will close a currently open
file and open the file it wanted to read.
In the past, that was a sufficiently great performance hit that someone decided
to put that message out to the alert log. It would be a mildly interesting
exercise to see if it would still be 'severe performance degradation'. Second
interesting test would be if the FD limit were set to a wildly low limit - such
as 4.
I hope this helps.
Kurt
On Wed, Nov 2, 2011 at 6:49 AM, Herring Dave - dherri
<Dave.Herring@xxxxxxxxxx<mailto:Dave.Herring@xxxxxxxxxx>> wrote:
I did a crazy thing the other day - reviewed an alert log from a system I
inherited a while ago. I found that after a recent auto-restart a message was
displayed: "WARNING:Oracle instance running on a system with low open file
descriptor limit. Tune your system to increase this limit to avoid severe
performance degradation.". Sure enough, on this system /etc/init.d/init.crsd
has the line "ulimit -n unlimited" in it, which on RHEL 4 generates an error,
so the FD limit defaults to 1024 (bug 5862719).
The problem is easy to resolve but my question is on Oracle's warning. How
could a low open file descriptor limit be a potential source of "severe
performance degradation"? Isn't it a black-or-white issue, either the limit is
high enough or if not, the db won't open/you can't add more datafiles?
DAVID HERRING
DBA
Acxiom Corporation
EML dave.herring@xxxxxxxxxx<mailto:dave.herring@xxxxxxxxxx>
TEL 630.944.4762<tel:630.944.4762>
MBL 630.430.5988<tel:630.430.5988>
1501 Opus Pl, Downers Grove, IL 60515, USA
WWW.ACXIOM.COM<http://WWW.ACXIOM.COM>
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