RE: should I analyze system statistics on ORACLE 10GR2?
Date: Fri, 4 Mar 2011 17:09:24 -0500
Message-ID: <009901cbdab8$d342a930$79c7fb90$_at_rsiz.com>
This is a common confusion between collecting statistics on the objects in the sys and system schemas versus collecting system statistics, which are the metrics of how the resources of the operating system respond.
If someone asks about system statistics the default understanding is the latter. I didn't decide to overload the use of these words, I'm just reporting the usage as I understand it for clarity. (Shades of partition for storage versus aggregate functions).
If I recall correctly JL has a post describing more in depth what I'll write as briefly as can: It is hazardous to performance to actually collect system statistics, because the tendency is to collect them any time other than when the system is at peak load. Plugging in decent numbers representative of the system capabilities at peak load will tend to help the optimizer to get things right. Feeding the optimizer unrealistic system statistics by any means, including collecting them at a period of near idleness will tend to make the optimizer add things up into bad choices.
mwf
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of Taylor, Chris David
Sent: Friday, March 04, 2011 10:11 AM
To: 'oratune_at_yahoo.com'; 'deshpande.subodh_at_gmail.com'; 'mccdba1_at_yahoo.com'
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Subject: RE: should I analyze system statistics on ORACLE 10GR2?
This is one of the areas that is really frustrating as a DBA.having to treat the SYS objects differently and THEN having to treat them differently in different databases. Some apps work well with SYS statistics, some fail miserably.
Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
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From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of David Fitzjarrell
Sent: Friday, March 04, 2011 8:17 AM
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Cc: oracle-l_at_freelists.org; oracle-db-l_at_groups.ittoolbox.com
Subject: Re: should I analyze system statistics on ORACLE 10GR2?
Collecting system statistics is really an 'it depends' situation since if you're running Siebel or SAP applications in 10g and later releases creating a job to collect system statistics can cause problems with performance ( the SAP team where I worked my last contract did NOT collect system statistics because when they tried it caused some critical query plans to change for the worse ). In other cases it may be acceptable and improve the performance of some queries so it's best to test this tactic before you implement in a production environment so the users aren't caught by surprise with dismal execution plans for queries that once ran acceptably.
David Fitzjarrell
From: Subodh Deshpande <deshpande.subodh_at_gmail.com>
To: mccdba1_at_yahoo.com
Cc: oracle-l_at_freelists.org; oracle-db-l_at_groups.ittoolbox.com
Sent: Thu, March 3, 2011 11:03:19 PM
Subject: Re: should I analyze system statistics on ORACLE 10GR2?
if you using cost based optimizer then you should collect stats..
I think...over a period earlier stats can be purged
thanks....subodh
On 17 February 2011 01:26, dba1 mcc <mccdba1_at_yahoo.com> wrote:
I saw a ORACLE document "Performance Tuning Guide for Siebel CRM Application on Oracle Part I - Cost-Based Optimization Guide" On this article it say "don't analyze system statistics":
System Optimizer Statistics
In 9i, Oracle introduced cpu_costing, a mechanism that allows the CPU cost of an operation to be included as part of the overall estimate. This feature is enabled in 9i only if you collect system statistics. This feature in 10g is enabled by default. Oracle Database 10g gathers two types of system statistics - statistics captured without a workload (noworkload) and statistics captured with a workload. In addition to CPU cost, disk I/O and memory utilization are also captured, to ensure that CBO picks the plan with the lowest estimated cost relative to other plans. Many Oracle DBAs attempt to leverage system optimizer statistics for further tuning of Siebel CRM application. Such actions may cause unpredictable degradation in performance of certain Siebel CRM application views and queries, and are strongly discouraged. We recommend that DBAs refrain from collecting system optimizer statistics, or altering any Oracle default settings pertaining to systems statistics.
I also see another ORACLE document say you need "analyze system statistics" to avoid stange thing happen.
Can Anyone tell me should I or Should NOT 'analyze system statistics"? Thanks.
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Received on Fri Mar 04 2011 - 16:09:24 CST