RE: I/O waits hurting anyone?

  • From: "McPeak, Matt" <vxsmimmcp@xxxxxxxxxx>
  • To: "Mark W. Farnham" <mwf@xxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 18 Feb 2014 17:47:18 +0000

Yes.. maybe I didn't ask the right question.

The reason this came up was because the DBAs had a report generated showing 
this SQL as the #1 in the database over the past week.  But it's only #1 in 
terms of elapsed time.

When I look at these things, I usually look for actual work: gets, physical 
reads/writes, cpu time, etc and ignore elapsed time.

The rationale being: if it is not doing a physical read/write and it is not 
using CPU, who cares?

So I am wondering if there is something else about "elapsed time" that makes it 
a good metric for identifying tuning targets.

Thanks,
Matt


From: Mark W. Farnham [mailto:mwf@xxxxxxxx]
Sent: Tuesday, February 18, 2014 12:31 PM
To: McPeak, Matt; 'ORACLE-L'
Subject: RE: I/O waits hurting anyone?

That depends largely on two factors:

1)    How much of your i/o "wait" is actually cpu/data movement, burning cpu.

2)    Whether your i/o is obstructing some other job's need for data access

mwf

From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx> 
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of McPeak, Matt
Sent: Tuesday, February 18, 2014 12:24 PM
To: ORACLE-L
Subject: I/O waits hurting anyone?

I have a process that executes a lot.  Over 6 days it's executed 1.3 million 
times.  The elapsed time per call averages 0.8 seconds, and the I/O wait time 
per call averages 0.7 seconds.

In other words, it spends most of its time waiting.

I'll look into all that... my question is more general: am I right in saying 
that the I/O waits don't load the system in any way and don't hurt any 
processes besides the one that is waiting?

Thanks in advance!

Matt

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