Re: [GENERAL] how to get accurate values in pg_statistic (continued)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Christopher Browne <cbbrowne(at)libertyrms(dot)info>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: [GENERAL] how to get accurate values in pg_statistic (continued)
Date: 2003-09-11 04:30:59
Message-ID: 21962.1063254659@sss.pgh.pa.us
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Christopher Browne <cbbrowne(at)libertyrms(dot)info> writes:
> The "right answer" for most use seems likely to involve:
> a) Getting an appropriate number of bins (I suspect 10 is a bit
> small, but I can't justify that mathematically), and

I suspect that also, but I don't have real evidence for it either.
We've heard complaints from a number of people for whom it was indeed
too small ... but that doesn't prove it's not appropriate in the
majority of cases ...

> Does the sample size change if you increase the number of bins?

Yes, read the comments in backend/commands/analyze.c.

> Do we also need a parameter to control sample size?

Not if the paper I read before writing that code is correct.

regards, tom lane

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