| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | mlw <markw(at)mohawksoft(dot)com> |
| Cc: | Zeugswetter Andreas SB SD <ZeugswetterA(at)spardat(dot)at>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Daniel Kalchev <daniel(at)digsys(dot)bg>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: again on index usage |
| Date: | 2002-01-11 19:09:21 |
| Message-ID: | 546.1010776161@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
mlw <markw(at)mohawksoft(dot)com> writes:
> ... Storage
> devices are now black boxes. The only predictable advantage a
> "sequential scan" can have on a modern computer is OS level caching.
You mean read-ahead. True enough, but that "only advantage" is very
significant. The 4.0 number did not come out of the air, it came
from actual measurements.
I think the real point in this thread is that measurements on an idle
system might not extrapolate very well to measurements on a heavily
loaded system. I can see the point, but I don't really have time to
investigate it right now. I'd be willing to reduce the default value of
random_page_cost to something around 2, if someone can come up with
experimental evidence justifying it ...
regards, tom lane
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