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Re: Equivalent praxis to CLUSTERED INDEX?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: Adi Alurkar <adi(at)sf(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Equivalent praxis to CLUSTERED INDEX?
Date: 2004-08-27 18:19:29
Message-ID: 1082.1093630769@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> Agreed.  What I am wondering is with our system where every update gets
> a new row, how would this help us?  I know we try to keep an update on
> the same row as the original, but is there any significant performance
> benefit to doing that which would offset the compaction advantage?

Because Oracle uses overwrite-in-place (undoing from an UNDO log on
transaction abort), while we always write a whole new row, it would take
much larger PCTFREE wastage to get a useful benefit in PG than it does
in Oracle.  That wastage translates directly into increased I/O costs,
so I'm a bit dubious that we should assume there is a win to be had here
just because Oracle offers the feature.

			regards, tom lane

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Subject: Re: Equivalent praxis to CLUSTERED INDEX?
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