From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@heroku.com>
cc: Jim Nasby <Jim.Nasby@bluetreble.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Less than ideal error reporting in pg_stat_statements
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Comments: In-reply-to Peter Geoghegan <pg@heroku.com>
 message dated "Sun, 04 Oct 2015 13:25:21 -0700"
Date: Sun, 04 Oct 2015 18:16:34 -0400
Message-ID: <30415.1443996994@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Peter Geoghegan <pg@heroku.com> writes:
> To be clear: I wasn't sure why you though I falsely count entries with
> dropped texts within entry_dealloc().

In the existing^H^H^Hprevious code, dropped-text entries would essentially
act as length-zero summands in the average calculation, whereas I think
we agree that they ought to be ignored; otherwise they decrease the
computed mean and thereby increase the probability of (useless) GC cycles.
In the worst case where the hashtable is mostly dropped-text entries,
which would for instance be the prevailing situation shortly after a GC
failure, we'd be calculating ridiculously small mean values and that'd
prompt extra GC cycles no?

			regards, tom lane


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