Re: "control file sequential read" on RAC
- From: "Norman Dunbar" <norman.dunbar@xxxxxxxxxxxxxxxxxxxxxxxxx>
- To: <gorbyx@xxxxxxxxx>, <shivaswamykr@xxxxxxxxx>
- Date: Tue, 15 May 2007 14:49:59 +0100
Afternoon all,
>> "Alex Gorbachev" <gorbyx@xxxxxxxxx> 05/15/07 01:28PM >>>
>> Seems like it's inefficient execution plan.
>> I know that Oracle might go crazy joining dictionary views and V$
>> views.
I've been told by Oracle trainers that joining a V$ view to an physical
table or other dictionary tyope objkect is fraught with danger because
:
* the V$ stuff is memory based and not protected by read consistency
* the V$ stuff changes frequently
When you join V$ to others, each time the V$ changes, Oracle starts the
query again. It only finishes when it manages to join all of V$ with
whatever without a change occurring part way through.
I used to join V$SESSION_WAIT to DBA_OBJECTS and performance was
abysmal :o(
Cheers,
Norman.
Norman Dunbar.
Contract Oracle DBA.
Rivers House, Leeds.
Internal : 7 28 2051
External : 0113 231 2051
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