Re: Separating data, index objects

From: Holger Baer <holger.baer_at_science-computing.de>
Date: Wed, 06 Jul 2005 14:52:15 +0200
Message-ID: <dagk60$kpq$1@news.BelWue.DE>

Paul wrote:
>
>
> DA Morgan <damorgan_at_psoug.org> wrote:
>
>

>>Separation of tables and indexes serves no useful purpose with respect
>>to scalability and performance.

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> Forgive me for jumping in here, but *_a priori_*, it seems obvious
> that it *_should_* serve such a purpose.

As soon as you start a sentence with it seems obvious, it *is* obvious that it *isn't* obvious. In other words: what you just said is wrong.
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> What is the mechanism by which Oracle prevents this from happening?
How are tables and indeces used?
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> Here, we are talking about tableX with indexX, but it does still make
> sense to separate different tables and indices to avoid contention -
> or is this not correct either?

No. You separate *segments* to spread I/O. If the segment in question is an index or a table has nothing to do with it.

And if you're not interested in the last 5% of possible performance, then SAME might very well serve this purpose.

You know, the error most people make regarding this topic, the don't think how an index is used.

An index is either
a) a mechanism to quickly retrieve a block from a table, or b) it can be used as a skinny version of a table.

If we're talking about a), then any session using an index will do so first and then retrieve the table block. So why should tables and indexes contend inherently more than tables and tables or indexes or indexes if we throw in multiuser?

If we're talking about b), then there is no table access at all and the whole discussion is moot.

My 0.02€
Holger Received on Wed Jul 06 2005 - 07:52:15 CDT