Re: Less than ideal error reporting in pg_stat_statements

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Peter Geoghegan <pg(at)heroku(dot)com>
Cc: Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Less than ideal error reporting in pg_stat_statements
Date: 2015-10-04 22:16:34
Message-ID: 30415.1443996994@sss.pgh.pa.us
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Peter Geoghegan <pg(at)heroku(dot)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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