(RE): Calculating LIOs

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Fri, 13 Aug 2004 10:27:12 -0600
Message-Id: <6.1.0.6.2.20040813102517.02fab400@pop.centrexcc.com>

At 10:02 AM 8/13/2004, you wrote:
>Excellent post mark. However, I have the following
>1 table query that does the following
>select col1, col2
>from table
>where primary_key = <value>
>The table has
>56 rows
>1 MB size. 128 blocks(so 8192 blocksize)
>My 10046 trace shows a full table scan with 63 logical IOs. Roughly half
>the number of blocks. Anyone know why? Looks like I am reading two blocks
>per LIO.
>I figure my number of blocks and bytes in the table by doing the following
>select blocks,bytes
>from dba_segments
>where segment_name = <table>

That's the allocated size. To get the number of blocks the table is actually occupying, or has ever occupied (HWM), use gather_table_stats and look at the dba_tables.blocks column, or use the dbms_space procedure.

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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Received on Fri Aug 13 2004 - 11:22:57 CDT