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Re: [PATCH] Improve EXPLAIN ANALYZE overhead by sampling

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
Cc: pgsql-patches(at)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Subject: Re: [PATCH] Improve EXPLAIN ANALYZE overhead by sampling
Date: 2006-06-01 06:47:06
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Lists: pgsql-hackerspgsql-patches
On Tue, May 30, 2006 at 10:01:49AM -0400, Bruce Momjian wrote:
> Patch applied.  Thanks.

I note Tom made some changes to this patch after it went in. For the
record, it was always my intention that samplecount count the number of
_tuples_ returned while sampling, rather than the number of
_iterations_. I'll admit the comment in the header was wrong.

While my original patch had a small error in the case of multiple
tuples returned, it would've been correctable by counting the actual
number of sample. The way it is now, it will show a bias if the number
of tuples returned increases after the first sampled 50 tuples.
However, my knowledge of statistics isn't good enough to determine if
this is an actual problem or not, since the way it is now will sample
more initialially...

Have a nice day,
Martijn van Oosterhout   <kleptog(at)svana(dot)org>
> From each according to his ability. To each according to his ability to litigate.

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