Oracle-L: RE: Prevent FTS

From: Fink, Dan <Dan.Fink_at_mdx.com>
Date: Mon, 06 Jan 2003 10:05:05 -0800
Message-ID: <F001.00527C06.20030106100505@fatcity.com>

Wny do you say that a FTS of table Z is bad? How many blocks has the table allocated (user_tables.blocks)? How many blocks will the query be returning? Is an index read really better? Use hints to test the different access paths and prove it.

FTS are not always bad. I have examples where a FTS is better when returning <1% of the rows of a table. I also have examples where returning 100% of the rows is more efficient when you use an index. It all depends on how many blocks you need to read, not the percentage of rows.

Dan Fink

-----Original Message-----
Sent: Monday, January 06, 2003 10:39 AM
To: Multiple recipients of list ORACLE-L

Hi All,

I've 3 tables table x,y,z
pk of x is (col_1,col_2),pk of y is (col_1,col_2,col_4,col_5),pk of z is (col_1,col_2)

where clause is :

where x.col_1 = y.col_1

and x.col_2 = y.col_2
and x.col_1 = z.col_1
and x.col_2 = z.col_2
and y.col_1 = z.col_1
and y.col_2 = z.col_2

and x.col_3 in ('val1','val2','val3')
and.....
..

Explain plan shows that there is a FTS of table z . what can be the reason for this and how to prevent this.

Thanks
Manoj

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Author:
INET: manoj.gurnani_at_orbitech.co.in

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Author: Fink, Dan
INET: Dan.Fink_at_mdx.com

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