Re: SeqScan costs

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: "Decibel!" <decibel(at)decibel(dot)org>, "Andrew Gierth" <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: SeqScan costs
Date: 2008-08-14 00:44:00
Message-ID: 18353.1218674640@sss.pgh.pa.us
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Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> That means going to the index meta page, find the fast root pointer, look up
> that page, look at the single leaf page pointer, look up that page, and do a
> binary search of the 200 leaf pointers. Once you find the resulting match,
> look up the heap page and *then* go directly to the right tuple.

Actually, the metapage access has been cached for some time, and there's
not going to be a separate root page if you only have 1 page worth of
index entries. But yeah, for large indexes there are going to be
multiple page accesses before you find what you want.

regards, tom lane

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