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Re: Thoughts on statistics for continuously advancing columns

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org, Nathan Boley <npboley(at)gmail(dot)com>
Subject: Re: Thoughts on statistics for continuously advancing columns
Date: 2009-12-30 03:08:33
Message-ID: 7216.1262142513@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> My thoughts on dealing with this intelligently without a major change to
> statstics gathering went along these lines:

> 1. add columns to pg_statistic to hold estimates of upper and lower
> bounds growth between analyzes.

This seems like a fundamentally broken approach, first because "time
between analyzes" is not even approximately a constant, and second
because it assumes that we have a distance metric for all datatypes.
(Note that convert_to_scalar does not assume that it can measure
arbitrary distances, but only fractions *within* a histogram bucket;
and even that is pretty shaky.)

I don't have a better idea at the moment :-(

			regards, tom lane

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