Oracle-L: Re: Big table, small table

From: Govindan K <gkatteri_at_omanmail.com>
Date: Tue, 30 Sep 2003 16:09:32 -0800
Message-ID: <F001.005D18AC.20030930160932@fatcity.com>

Are you using any trunc functions while querying. Do this. SELECT column_name,count(*) from small_table group by column_name;
Run this for all the tables. My guess is that atleast 30% of the rows in the
small table is for the value that you gave. So the optimizer is forced to read
the index first followed by data read. When you drop the index, it does a FTS.
Hence it is faster.

HTH
GovindanK

<-----Original Message----->

From: Sherrie.Kubis_at_swfwmd.state.fl.us Sent: 9/29/2003 6:01:55 AM
To: ORACLE-L_at_fatcity.com

I have five tables, three are > 3 million rows, one is a little more than 1
million, one a little less than one million. All tables are structured the same, with the same indexing, just different
types of data. There is a date column
with a normal index.

A query with a 'between' on the date column against the largest table screams. Any of the largest tables are
acceptable performance. The smallest is extremely slow, while the million
row table sits around for 20 minutes
or so.

If I remove the index from the million row table, I get acceptable results.
All of the tables and indexes are
analyzed.

Why would taking an index off make this query faster? What doesn't the CBO
know that not using an index
is the best path?

Sherrie Kubis
Southwest Florida Water Management District 2379 Broad Street
Brooksville FL 34604-6899

Phone: (352) 796-7211, Ext. 4033
Fax: (352) 754-6776
Email: Mailto:Sherrie.Kubis_at_swfwmd.state.fl.us http://WaterMatters.org

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INET: Sherrie.Kubis_at_swfwmd.state.fl.us

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Author: Govindan K
INET: gkatteri_at_omanmail.com

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