Oracle-L: slowish query causing problems...

From: Denham Eva <EvaD_at_TFMC.co.za>
Date: Tue, 14 Jan 2003 03:29:14 -0800
Message-ID: <F001.0052EE16.20030114032914@fatcity.com>

Hello List,

Pls help me on this problem. Our application does a validation when it uses a certain screen, as it so happens this screen is used very intensively. The performance is very slow, I have isolated the main culprit. I have tried the following.
I have dropped all the indexes and tried recreating them individually. Each time I have run an explain plan on the query, the optimizer (both rule and Choose) have chosen to do a FULL table scan on the fwepcode table. Even when using a hint to explicitly use the index it still uses FULL. This is very frustrating indeed.

SELECT DISTINCT (1)

           FROM fwepcode1
          WHERE (wotype = 'TST' AND func = 'C0NEPRF' AND EXP = '22222')
             OR 'INPRG' NOT IN (SELECT VALUE
                                  FROM valuelist
                                 WHERE listname = 'STATUS'
                                   AND MAXVALUE = 'AAAAA')

Is the reason that the optimizer does not use any of the indexes because of the SELECT DISTINCT (1)?
I have tried adjusting this query slightly to remove this and it still insists on doing a full table scan.
Funny enough the sub query on valuelist table does use a index. The table contains 8920 rows. The cost according to the explain plan is 703 and bytes 9834.

The system is a Oracle 817 on Win2k.

Pls advise, any options or help will be appreciated. Many Thanks
Denham Eva
Oracle DBA
"UNIX is basically a simple operating system, but you have to be a genius to understand the simplicity."
Dennis Ritchie.

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Author: Denham Eva
INET: EvaD_at_TFMC.co.za

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