Re: Calculating LIOs

From: Tanel Põder <tanel.poder.003_at_mail.ee>
Date: Fri, 13 Aug 2004 19:02:43 +0300
Message-ID: <062901c4814e$f7b2aa10$71849fd9@porgand>

Hi!

> UNIQUE SCAN followed by a TABLE ACCESS BY ROWID. Well, how big is the =
> index? How many levels? Remember that regardless of the value =
> specified in the pk_column predicate, the number of levels from the =
> index root block to any leaf block is always the same. So, if the index =
> has a BELVEL of, say, 3, then to get from the root to the leaf =
> containing 123 will be 4 buffer gets. The TABLE ACCESS BY ROWID is one =
> more buffer get. So, that's a total of 5 buffer gets. =20

Also, the LIO count may increase when Oracle has to construct a read consistent clone of index/datablocks...

Tanel.

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Received on Fri Aug 13 2004 - 10:58:42 CDT