FULL SCAN COST ?

[Sofiane]

Hello,


I tried to find the following statement cost :

select * from T1

T1 is composed of : 22064 blocks and the db_file_multiblock_read_count=64.

For full scan, I used : Cost = blocks/db_file_multiblock_read_count
and so the cost is around 345

Using autotrace, the cost given by Oracle is about 850...
I did the test with db_file_multiblock_read_count=32. Oracle find about 1700 (my value is 850).

Any explanation ? How Oracle find 850 ?

(blocks = 22064, empty block = 1240, db_block_size=4ko, 30o/rows, 850000 rows...).


thanks in advance

Sofiane

[chrisrlong]

Inasmuch as I admire your effort, I fear it is in vain. The Cost that Oracle calculates is useful only to itself, and holds no relationship to the real world.

Here are just a couple of the threads where we have addressed the value of 'COST'

http://www.dbasupport.com/forums/sho...threadid=12384

http://www.dbasupport.com/forums/sho...threadid=11868


- Chris