performance impact of optimizer_search_limit

From: Wilkes, Steve <steve.wilkes_at_npower.com>
Date: Mon, 04 Jun 2001 04:18:23 -0700
Message-ID: <F001.00319FD7.20010604035521@fatcity.com>

Hi,

Oracle 8.0.5
AIX 4.3.3 I have improved the response time of one of my 8 table join queries by increasing optimizer_search_limit from the default 5 to 8. At the value of 8 the plan changes and has made a 10 min query run in under 5 seconds. The optimizer is set to CHOOSE with the statistics up to date and a sample size of 20%. This is a third party application and I don't have access to the source code to add hints. The value of optimizer_max_permutations has been left at 80000.

I know that this makes the optimizer now check 8!=40320 permutations instead of 5!=120 permutations. I expect the parse time to increase but does anyone have any experience as to the performance impact that this may have? Any horror stories?

Thanks in advance.

Steve Wilkes

---

Oracle DBA
npower

---

This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify gpupower.co.uk or postmaster_at_npower.com

This outgoing e-mail (and any attachments) has been checked
(using Sophos Sweep 3.45 + patches) before leaving us (UK 08457 353637),
and has been found to be clean from any virus infection.

---

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Wilkes, Steve
  INET: steve.wilkes_at_npower.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L


(or the name of mailing list you want to be removed from).  You may

also send the HELP command for other information (like subscribing).

Received on Mon Jun 04 2001 - 06:18:23 CDT