From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Greg Stark <gsstark(at)mit(dot)edu> |
Cc: | Richard Huxton <dev(at)archonet(dot)com>, David Brown <time(at)bigpond(dot)net(dot)au>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Seqscan rather than Index |
Date: | 2004-12-17 18:36:52 |
Message-ID: | 21610.1103308612@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Greg Stark <gsstark(at)mit(dot)edu> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> I think the one effect that's not being modeled is amortization of index
>> fetches across successive queries.
> And across multiple fetches in a single query, such as with a nested loop.
Right, that's effectively the same problem. You could imagine making a
special-purpose solution for nestloop queries but I think the issue is
more general than that.
> It seems like the effective_cache_size parameter should be having some
> influence here.
But it doesn't :-(. e_c_s is currently only used to estimate
amortization of repeated heap-page fetches within a single indexscan.
regards, tom lane
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