Re: contsel and gist

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ben <midfield(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: contsel and gist
Date: 2010-10-28 17:50:24
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Ben <midfield(at)gmail(dot)com> writes:
> my guess is that it has to do with the selectivity of the @> operator. i've looked and noticed that the selectivity functions for @> and other period operators are basically stubs, with constant selectivity. my questions are :

> 1 - am i wrong in my assessment? is the constant contsel, areasel, etc hurting us?

The stub selectivity functions definitely suck.

> 2 - how hard would it be to implement contsel et al for period data types?

If it were easy, it'd likely have been done already :-(

However, having said that: the constant value of the stub contsel
function is intended to be small enough to encourage use of an
indexscan. Maybe we just need to decrease it a bit more. Have you
investigated what the cutover point is for your queries?

regards, tom lane

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