RE: Is my Oracle Server issuing more IO than it can handle
Date: Tue, 7 Dec 2010 11:04:48 -0600
If you're going to post to the list, I'd personally rather address someone with a name. (From my own skeptical mind I want to question the motive behind not giving a real name, or semi-real name)
You're questions show a pretty good understanding of some underlying principles - so I'm a little concerned what your angle is. Again, it may just be my skepticism, or you may in fact be angling for some information to use in a manner inconsistent with the principles of this list.
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
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From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Oracle Dba Wannabe
Sent: Tuesday, December 07, 2010 10:36 AM
Subject: Is my Oracle Server issuing more IO than it can handle
Hi All, this is a 10.2.0.4 single instance database (non asm). I see the following events from awr (1 hour snapshot - however hourly snapshots after this show the same trend with respect to wait events): Event
% Total Call Time
free buffer waits
log file switch (private strand flush incomplete)
log file sync
buffer busy waits
db file parallel write
I know that db file parallel write only contributes to 5% of the total call time - but its avg wait time looks extremely poor - that and the fact that free buffer waits appear at top indicate that there's a db writer issue (db_writer_processes=4) - which leads me to believe perhaps its the IO subsystem. Now the storage team report there is nothing up with the storage. I was hoping someone could help with the following questions: 1. Is there someway from awr that I can determine that the Oracle server is issuing more IO than the storage system can handle for example: Physical reads:
Phy Reads + Phy Writes = 1372 IOPS
Can I then say that if each disk can do 100 IOPS, that the storage system should at least have 13 Disks? (13x100 IOPS)? Or is that an over simplification?
2. Interestingly this DB server was moved onto a new box with a different storage and the issue is no longer observed there. Transactions Per Second on old box = 57.22 Transactions Per Second on new box = 225 Phy Reads + Phy Writes for New Box, are slightly under half compared to the old box: Physical reads:
That said, the redo size per second on the new box is twice that of the old box (7mb/s : 3mb/s). The buffer cache and db writer processes are the same on both boxes.
Other than the storage aspect of things, I'm thinking (and will check) whether theres an o.s/kernel misconfiguration w.r.t to async io, etc that might be causing this on the old box.
Appreciate any thoughts on 1 or/and 2