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RE: Re: quick suggestions for tuning ?

From: Stephane Faroult <>
Date: Mon, 11 Aug 2003 08:24:23 -0800
Message-ID: <>

>Thanks a lot Stephane.
>There are indexes on profile table which u pointed
>but none of the tables/indexes are analyzed yet.

  First thing to do.

>Connor pointed that there are 54million consistent
>LIO is high.
>does it mean that db_cache_size (700M) is small ?
>how to deal with this ?
>Can u throw some light on this Stephane ?

db_cache_size has nothing to do with LIOs. LIOs are the number of blocks you need to visit to return an answer to your queries. Physical layout may influence it (by 'physical layout' I mean how dense the data is in your blocks, not where you put it on disk) but it mostly depend on what you are asking and how you are asking it, memory has nothing to do with it. If you haven't allocated enough memory, you will do more PIOs, but reduce LIOs in no way. Let's take a stupid analogy : say that LIOs are a big heap of sand you wish to move from one place to another. Having too small a SGA is like using a tea-spoon to do it. Obviously, using a shovel will be better. But you'll move as much sand in the end. To reduce LIOs you must optimize the code - make Oracle visit much fewer blocks, first of all, which may be achieved by a number of means. Indexes are obvious but quite often, for large volumes, full scans may be more efficient - try not to have any prejudice. Check what Oracle does (execution plans), try alternate ways to write the same query. SET AUTOTRACE ON TRACEONLY + SET TIMING ON are very useful under SQL*Plus. Once the size of your sand heap has dwindled to almost nothing, you may decide that perhaps a bigger spoon would work better, but this is the very last thing to contemplate.

HTH, Stephane Faroult

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Author: Stephane Faroult

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Received on Mon Aug 11 2003 - 11:24:23 CDT

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