Re: Updates with correlated subqueries slow after 9.2->10.2 upgrade

From: Robert Freeman <>
Date: Wed, 18 Nov 2009 08:56:37 -0800 (PST)
Message-ID: <>

I'm just wondering.. In your move from 9i to 10g, did you generate system statistics? While I doubt it will make a difference, it might be worth trying. Probably even less important are fixed table statistics, etc...


 Robert G. Freeman
Oracle ACE
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From: Neil Kodner <> To:
Sent: Tue, November 17, 2009 3:02:23 PM
Subject: Updates with correlated subqueries slow after 9.2->10.2 upgrade

Now that things are slow and unresponsive, I've been asked to join the fray.

Little bit of background:
DW-type environment
4 CPU Solaris 10
optimizer_index_caching 90
optimizer_index_cost_adj 50

I didn't set the optimizer parameters, I'm of the 'leave them alone' school.

Once our environment was upgraded from to, everything seemed ok except for UPDATE statements that contain correlated select statements. Across the board, we received poor performance compared to running them in 9.2.

Another disclaimer-I didn't write this query-but it ran in 3 minutes in 9i.

Altering the session and setting optimizer_index_cost_adj=100 and optimizer_index_caching=0 didn't make a difference.

A common denominator is that the session-altered plans have a SORT UNIQUE step and the default 10g plans do not.

Rather than clutter up the post with the queries and 2 versions of explain plans, I wrote everything to a file on my site.

Would love to hear help/feedback/whatever - I'm struggling with this and altering the session each time is unacceptable.

Received on Wed Nov 18 2009 - 10:56:37 CST

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