Re: Question on gathering System Statistics
Date: Thu, 28 Jan 2021 11:44:46 +0000
Message-ID: <DB7PR10MB209040C214FB69FB0BD548D085BA9_at_DB7PR10MB2090.EURPRD10.PROD.OUTLOOK.COM>
Unsurprisingly, I agree with Jonathan.
The official Oracle line is (10 - gather system stats, 11 gather system stats, 12+ don't gather system stats - use the defaults***) They fundamentally affect the optimizer costings. If they aren't set, don't set them***. If they are set, understand what setting them has changed in terms of the optimizer. It can really affect the calculation between single block reads and multiblock reads, changing the balance between favouring selective index access versus full table or fast full index scans. From a stability perspective, you should leave them alone.
Neil Chandler
***there are exceptions to this, but my general rule is to leave as default in all releases of Oracle
From: oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> on behalf of Jonathan Lewis <jlewisoracle_at_gmail.com> Sent: 28 January 2021 11:08
To: oracle-l_at_freelists.org <oracle-l_at_freelists.org> Subject: Re: Question on gathering System Statistics
A key question to ask first is whether you had system stats set/collected on the vmax250 and whether this was done in combination with setting the db_file_multiblock read count or leaving it to default, and had you done anything with the calibrate_io option? Ideally you probably want to believe that if you get the same plans with the Powermax you'll get the same, or better, performance. But if you do something that changes the optimizer's arithmetic you may get plan changes that result in random variations in performance.
If you don't know what you've done about system stats in the past there's a script at the end of this blog note that will report them for you: https://jonathanlewis.wordpress.com/2019/08/14/gather_system_stats/<https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fjonathanlewis.wordpress.com%2F2019%2F08%2F14%2Fgather_system_stats%2F&data=04%7C01%7C%7C7549f66e8e574167703808d8c37d08e0%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637474289095264596%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=cqbbmCDPiThkNr7rcbv3PoE6FAiRTM%2BD9f9a4DD1Mz4%3D&reserved=0>
Regards
Jonathan Lewis
On Tue, 26 Jan 2021 at 19:30, Hameed, Amir <Amir.Hameed_at_xerox.com<mailto:Amir.Hameed_at_xerox.com>> wrote:
Hi,
We are in the process of moving our applications from current storage array (VMAX250) to a new array (Powermax). From best practices standpoint, should we collect System Stats after moving to the new storage? If we should then is there a recommended way of gathering System Stats?
Thanks,
Amir
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