Oracle-L: RE: CBO not using the index even though it is faster when hinted

From: Johnson, Michael <Michael.Johnson_at_oln-afmc.af.mil>
Date: Fri, 24 Jan 2003 12:38:56 -0800
Message-ID: <F001.0053A0B7.20030124123856@fatcity.com>

All the columns in the table are not null ...

here is an interesting test I ran ...

several Direct_Path_Write and Read waits with large elasped times are showing up in the 10046 trace data on this query due to the full table scan.

Just deleted statistics on this and fwiw ...

With Statistics ....

SELECT Statement Optimizer=Choose (Cost=225 ...) SORT (Order By) (Cost=225 ...)
Table Access (Full) of 'table1'

Physical Reads = 433

Without Statistics ..

SELECT Statement Optimizer=Choose
Table Access (By Index Row) of 'table1

Index ( Full Scan ) of 'concatenated index' (Non-Unique)

Physical Reads = 0

Mike

-----Original Message-----
Sent: Thursday, January 23, 2003 6:29 PM To: Multiple recipients of list ORACLE-L ....

Anyone have any problems with the CBO not using a index when you know it is faster by forcing a hint ?

I have set the following ...

Solaris
Oracle Version 8.1.7.4

block size = 8
DB_FILE_MULTIBLOCK_READ_COUNT = 8
mode = Choose

also using Tim Gormans 90 and 50 values for the other optimizer parms.

Select col1, col2, col3, blah1, blah2 from table order by col1, col2, col3;

Concatenate index on col1, col2, col3.

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Author: Johnson, Michael
INET: Michael.Johnson_at_oln-afmc.af.mil

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Author: Johnson, Michael
INET: Michael.Johnson_at_oln-afmc.af.mil

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