Comments on: Finding the reasons for excessive logical IOs

By: Dynamic tracing of Oracle logical I/O « Alexander Anokhin

Dynamic tracing of Oracle logical I/O « Alexander Anokhin — Thu, 01 Dec 2011 10:29:29 +0000

[...] The tool can be especially helpful in 11g because x$kcbsw (x$kcbuwhy in 11g) is not populated properly there. Note: Examples of using view x$kcbsw: – Investigating Logical I/O by Jonathan Lewis – Finding the reasons for excessive logical IOs by Tanel Poder [...]

By: JoeG

JoeG — Tue, 08 Nov 2011 14:55:52 +0000

Tanel,

We are experiencing high logical IO intermittently on a table insert. The table has 314 columns. It has 10 indexes, only an update trigger and 1 PK constraint. It is an INSERT tbl1 col1… values(val1….) type of SQL. Most of the time the insert completes in less than 1 second. We have applied patches from Oracle (11.2 BP10 & 10205201) but still face issues intermittently on INSERTS. The SELECT statements have not had any performance issues.

Is there a table or view that shows when the table needs to extent as your site is the first one I have seen that talks about high logical IO.

Any help or insites would be much appreciated.
Regards,
Joe

By: Tanel Poder

Tanel Poder — Fri, 25 Dec 2009 05:19:33 +0000

Jonathan Lewis has also written about this topic:

http://www.jlcomp.demon.co.uk/buffer_usage.html

By: Tanel Poder

Tanel Poder — Fri, 25 Dec 2009 05:09:02 +0000

Well, I guess you have to read through it once more then!

What I have highlighted in the output is section with *BUFG*.

And earlier in the note I have documented that BUFG means “Buffer get reasons”.

If you’re doing too many buffer gets, you want to know WHY. And the reasons section will tell you that. For example this approach has allowed me to diagnose a problem with ASSM space allocation code in kernel, where majority of buffer get reasons started with KTS and for most of these the reason was reported as ktspscan_bmb in BUFG output).

By: willem

willem — Thu, 24 Dec 2009 22:10:56 +0000

Long output, yes. I don’t get the point though. How to know if the output points to a problem?

By: Hans-Peter

Hans-Peter — Thu, 03 Dec 2009 07:34:45 +0000

Hi Tanel,

Nice stuff!
I look forward for the follow up.

Regards Hans-Peter

By: Blogroll Report 13/11/2009-20/11/2009 « Coskan’s Approach to Oracle

Blogroll Report 13/11/2009-20/11/2009 « Coskan’s Approach to Oracle — Mon, 23 Nov 2009 01:59:19 +0000

[...] 17-How to find reasons excessive LIO? Tanel Poder-Finding the reasons for excessive logical IOs [...]

By: Haris

Haris — Fri, 20 Nov 2009 08:44:13 +0000

Hi Tanel

Very informative.

By the way, can you please give some interpretation the important point from the output and where actually the problem which caused the excessive logical IOs.

Thanks in Advance.

Cheers!

By: Tanel Poder

Tanel Poder — Fri, 20 Nov 2009 04:16:43 +0000

Thanks!

By the way I fixed a typo – kill -STOP suspends the process (not kill -SUSP as I wrote earlier)…

By: Dion Cho

Dion Cho — Fri, 20 Nov 2009 03:06:34 +0000

Tanel.

Good stuff as always. This would be a good example on how a simple question turns out to be a big knowledge.