From: | Lincoln Yeoh <lyeoh(at)pop(dot)jaring(dot)my> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostGreSQL <pgsql-general(at)postgresql(dot)org> |
Subject: | Re: Forcing use of indexes |
Date: | 2003-04-03 04:59:57 |
Message-ID: | 5.1.0.14.1.20030403124101.026b0b60@mbox.jaring.my |
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Thread: | |
Lists: | pgsql-general |
At 09:52 AM 4/2/03 -0500, Tom Lane wrote:
>shared_buffers doesn't affect the estimated cost of an indexscan.
>effective_cache_size does, also random_page_cost, but you didn't mention
>having touched those.
Hi,
If my O/S has a cache of say 1GB and my DB is < 1GB and is totally in cache
would setting effective_cache_size to 1GB make the optimizer decide on
index usage just as setting random_page_cost to 1?
If random page cost is high but so is effective_cache_size does postgresql
use sequential scans first time round and then index scans second time
round if everything cached? Of course if random page cost is 1 then always
use index scan even for first read. This is probably "academic" and not
really an issue for real world.
But the main thing is: is it hard for the optimizer to tell whether a
DB/table/index is completely in effective_cache_size?
There's mention of something like this (see below), but the final
suggestion in thread was to set random_page_cost to 1, so I'm wondering how
one would use effective_cache_size.
Brian Hirt (bhirt(at)mobygames(dot)com)
Re: Performance Tuning Question
Date: 2002-09-09 10:17:52 PST
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&safe=off&selm=1031586091.1345.722.camel%40loopy.tr.berkhirt.com&rnum=3
Regards,
Link.
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