Re: "Bug" in statistics for v7.2?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Zeugswetter Andreas SB SD" <ZeugswetterA(at)spardat(dot)at>
Cc: "Marc G(dot) Fournier" <scrappy(at)hub(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: "Bug" in statistics for v7.2?
Date: 2002-02-15 17:45:39
Message-ID: 14858.1013795139@sss.pgh.pa.us
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"Zeugswetter Andreas SB SD" <ZeugswetterA(at)spardat(dot)at> writes:
> The pg_stats values are only, um, statistical. If 99.9% of the table is
> the same value and the other four values appear only once or twice, it's
> certainly possible for ANALYZE's sample to include only the common value
> and miss the rare ones. AFAIK that will not break anything; if you have
> an example where the planner seems to be fooled because of this, let's
> see it.

> Hmm ? How about select * from xxx where profiles_faith = 7
> would estimate all rows, no ? Instead of 2.

Not in 7.2 ... nor in previous versions AFAIR.

> That is why I think a bin for "very uncommon" values could also be
> useful sometimes.

Perhaps you should experiment or read the code before opining...

regards, tom lane

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