Re: Updates with correlated subqueries slow after 9.2->10.2 upgrade
- From: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
- To: Neil Kodner <nkodner@xxxxxxxxx>
- Date: Tue, 17 Nov 2009 15:00:11 -0800
A 100% sample will generally be OK for single table cardinality, but
it may not mean the join cardinality is accurate.
Look at the plan line #2 in the first example.
The HASH JOIN version has a cardinality of 8775, the HASH JOIN RIGHT
SEMI version has a cardinality of 19. That's a difference of 462x.
Pretty big!
How many rows are really returned?
In the second example the access order and path is identical, the only
difference being lines 6 & 9 where one is SORT UNIQUE and the other is
HASH UNIQUE. I'm wondering how much difference there really is
between these two. I would think very little, but what is it?
On Tue, Nov 17, 2009 at 2:28 PM, Neil Kodner <nkodner@xxxxxxxxx> wrote:
> I'm using
> estimate_percent=>100 and method_opt=>'FOR ALL COLUMNS SIZE 1' for these
> tables
--
Regards,
Greg Rahn
http://structureddata.org
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