From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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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 |
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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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