RE: Accessing ASH is slow

  • From: John Hallas <John.Hallas@xxxxxxxxxxxxxxxxxx>
  • To: "mwf@xxxxxxxx" <mwf@xxxxxxxx>, 'ORACLE-L' <oracle-l@xxxxxxxxxxxxx>
  • Date: Mon, 29 Jul 2013 08:20:41 +0100

I have just presented a talk at a UKOUG SIG about how we built our AWR 
repository and the benefits we have achieved.
There are two main points that I would make

It can be cost neutral - you don't need a multi-CPU server, most of the time 
you will be running single queries and you wont have many users who can logon. 
More importantly disk can be tier 3 and by compressing the loaded AWR (and ASH) 
data along with reducing the retention of production to 7 or 14 days then no 
additional disk is required.

Secondly, once you have the repository it can be used for a number of reasons - 
holding performance test data, comparing performance pre-release with 
post-release, capturing OEM unix data and storing that etc etc.


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Mark W. Farnham
Sent: 22 July 2013 20:00
Subject: RE: Accessing ASH is slow

I defy anyone to state a useful operational definition of "best practice"
that is not self-contradictory. (For starters, knowing that something is
"best" requires either a logical construct with agreed premises that proves
no other practice can be better, or else an enumeration of all possible
practices and agreement that each of them is inferior. I suggest you try for
perpetual motion first.) That pet peeve out of the way:

I personally think it is a bad practice to consume production RDBMS cycles
doing ad hoc analysis of metrics.

Rather, I would suggest that such data should be copied (meaning some data
transport, but reading any given window of data only once) into a
datawarehouse for the DBA.
The destination schema would of course *NOT* be sys, Gormanesque scaling to
infinity is plausible, and you can feel free on your DBA datawarehouse to
add indexes and aggregates to your heart's content.

Note that I have not opined on standard reports that pretty much scan
everything once occasionally (like ADDM) as regards consuming production
resources, nor on the expense of collection of the standard metrics now
built into Oracle. If you're licensed to use them, it seems likely the
collection of such metrics is worthwhile, even if only for the insurance
value that they exist. (If you're not licensed to use them that is a
financial statement on the value of performance to your organization. Since
your question involves ASH, it seems likely you have the appropriate

IF Oracle provided an option to deposit metric collection results in a
destination other than the production database, I tend to think that would
work out nicely in conserving overall throughput (though there is
potentially a network traffic argument if the repository is off of the
physical host of the production database.)

Of course if the resources to set up a warehouse for the DBA are not
available, then you're stuck on the production database. Whether pulling SYS
contents you want to repeatedly analyze into a different schema you can
safely manipulate is an effective strategy probably varies from case to


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