Re: parsing puzzle

  • From: Joe A-C <jwc7744@xxxxxxxxx>
  • To: andrew.kerber@xxxxxxxxx, Cary Millsap <cary.millsap@xxxxxxxxxxxx>
  • Date: Fri, 9 Apr 2010 14:14:17 -0700 (PDT)

But it seems that if the reports consistently show the same results you can 
assume that they are reliable. In  my case I've looked at about 25 reports and 
they show the same top wait events when the system is slow. This is not the 
case when the system is performing ok.

Also, even though the reports are not gathering data from every session it is 
taking a sampling of the sessions and as long as the sample is large enough 
then statistically I would think that they are representative of the whole. The 
key of course is the sampling size.

I understand what you're saying about a particular session causing a problem 
but being buried in a lot of other data. I have in the past increased the 
intervals to 10 minutes which would seem to help this issue. 

The reports have always helped in the past but if they don't help soon in this 
case I'll be looking at other tools.


--- On Fri, 4/9/10, Cary Millsap <cary.millsap@xxxxxxxxxxxx> wrote:

From: Cary Millsap <cary.millsap@xxxxxxxxxxxx>
Subject: Re: parsing puzzle
To: andrew.kerber@xxxxxxxxx
Cc: Brandon.Allen@xxxxxxxxxxx, "Joe A-C" <jwc7744@xxxxxxxxx>, 
"oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
Date: Friday, April 9, 2010, 4:57 PM

It's just really difficult to tell when AWR results are useful and when they're 
not. That is what unreliable is, by definition. A problem with even small 
snapshot intervals is that you're snapping data from potentially thousands of 
sessions that can still bury the data you really need to be looking at from one 
special session that you're trying to diagnose.

Cary Millsap
Method R Corporation

On Fri, Apr 9, 2010 at 2:51 PM, Andrew Kerber <andrew.kerber@xxxxxxxxx> wrote:

That seems unlikely, the wait events are consistent.  However, If you want a 
short term snapshot though, run this command:

exec dbms_workload_repository.create_snapshot

at whatever interval you want.

On Fri, Apr 9, 2010 at 2:22 PM, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> 

Because they report instance-wide stats, they could be showing you wait events 
for processes that are completely unrelated to the problems you're trying to 
troubleshoot.  And also since they are (usually) at infrequent intervals, 
transient problems can easily be buried by other more persistent events.  For 
example, a session that hangs for 5 minutes blocked by another transaction's 
blocking lock - this 5 minute delay could be a major problem for some business 
critical function that you're trying to troubleshoot, but if you look at an AWR 
report over a 1 hour interval, those 5 minutes of waiting on the blocking 
lock/enqueue aren't likely to show up in your top wait events.



-----Original Message-----

From: Joe A-C [mailto:jwc7744@xxxxxxxxx]

Why do you say that the AWR reports are likely to be misleading?

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Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'


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