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From: Steve Atkins <[email protected]>
To: PostgreSQL General <[email protected]>
Subject: Re: index vs. seq scan choice?
Date: Thu, 24 May 2007 21:25:23 -0700
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <8C5B026B51B6854CBE88121DBF097A86C3A30D@ehost010-33.exch010.intermedia.net>
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On May 24, 2007, at 8:26 PM, Tom Lane wrote:

> "Joshua D. Drake" <[email protected]> writes:
>> Tom Lane wrote:
>>> I'm not sure I want to vote for another 10x increase by
>>> default, though.
>
>> Outside of longer analyze times, and slightly more space taken up  
>> by the
>> statistics, what is the downside?
>
> Longer plan times --- several of the selfuncs.c routines grovel  
> over all
> the entries in the pg_statistic row.  AFAIK no one's measured the real
> impact of that, but it could easily be counterproductive for simple  
> queries.

The lateness of the hour is suppressing my supposed statistics savvy,
so this may not make sense, but...

Would it be possible to look at a much larger number of samples  
during analyze,
then look at the variation in those to generate a reasonable number of
pg_statistic "samples" to represent our estimate of the actual  
distribution?
More datapoints for tables where the planner might benefit from it,  
fewer
where it wouldn't.

Cheers,
   Steve

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