Re: Performance impact of MONITORING and GATHER_STALE
- From: Mladen Gogala <mgogala@xxxxxxxxxxxxxxxxxxxx>
- To: Leng.Kaing@xxxxxxxxxxx
- Date: Tue, 15 Mar 2005 10:26:40 -0500
Leng Kaing wrote:
>
>Hi guys,
>
>
>
>Apologies if I'm revisiting a beaten path but I've tried to search the
>archive, metalink and google and couldn't find my answer (or it may have
>been hiding). So I'll ask the question (again)...
>
>
>
>What is the performance impact of turning on MONITORING at the table
>level? Ie. ALTER TABLE x MONITORING. Will it have a negative impact on
>our production system?
>
>
Leng, I am running 9.2.0.5 on Solaris, all my production tables are in
the monitoring mode and there
are no adverse effects on my production database. The explanation is
simple:
When tables are in monitoring mode (default in 10g), the only things
that are update are memory tables (X$).
As Mr. Litchfield has shown, those tables are not protected by the
transaction mechanisms, which makes
updating them much cheaper. Unless you already have CPU bound system,
you will not suffer from performance
degradation if you enable monitoring for 250 tables, like I did.
It also takes away any purpose from gathering statistics based on STALE
status. Niall has demonstrated that SYS.DBA_TAB_MODIFICATIONS, the
entity behind "dbms_stats.gather_stale" will record inserts, even if those
are eventually rolled back. A single failed load with SQL*Loader can
have no effect whatsoever on the table itself,
but cant invalidate your statistics and trigger an expensive DBMS_STATS job.
Unrelated to that, I've been warned about the mistake I was consistently
making in our communications
and I have to humbly apologize.
--
Mladen Gogala
Oracle DBA
Ext. 121
--
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