Re: Low FD limit a performance issue?
- From: Kurt <kurtengelo@xxxxxxxxx>
- To: Dave.Herring@xxxxxxxxxx
- Date: Wed, 2 Nov 2011 16:31:45 -0700
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> 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
> TEL 630.944.4762
> MBL 630.430.5988
> 1501 Opus Pl, Downers Grove, IL 60515, USA
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