Re: Is my Oracle Server issuing more IO than it can handle

From: OKH <>
Date: Tue, 7 Dec 2010 18:05:38 +0100
Message-Id: <>

There is also another thing. Your log files are too small and you have too few of them. I suppose your log files and data files share the same disk(s).

Felix Castillo Sanchez

Am 07.12.2010 um 17:35 schrieb Oracle Dba Wannabe <>:

> Hi All, this is a 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 Waits Time(s) Avg Wait(ms) % Total Call Time Wait Class
> free buffer waits 17,926,869 193,146 11 67.7 Configuration
> log file switch (private strand flush incomplete) 41,550 30,538 735 10.7 Configuration
> log file sync 211,675 25,156 119 8.8 Commit
> buffer busy waits 42,093 23,218 552 8.1 Concurrency
> db file parallel write 376 14,274 37,963 5.0 System I/O
> 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: 954.74 16.68
> Physical writes: 418.89 7.32
> 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: 243.02 1.08
> Physical writes: 564.62 2.51
> 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
> Thanks

Received on Tue Dec 07 2010 - 11:05:38 CST

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