From: Andrew Gierth <andrew@tao11.riddles.org.uk>
To: Andres Freund <andres@anarazel.de>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alexander Kuzmenkov <a.kuzmenkov@postgrespro.ru>
Cc: pgsql-hackers@lists.postgresql.org
Subject: Re: Performance improvements for src/port/snprintf.c
Date: Thu, 27 Sep 2018 04:53:27 +0100
Message-ID: <87r2hffwda.fsf@news-spur.riddles.org.uk> (raw)
In-Reply-To: <20180927005705.shbl3n5hq3t65n2j@alap3.anarazel.de>
References: <11787.1534530779@sss.pgh.pa.us>
<2238.1534716465@sss.pgh.pa.us>
<f5dd41da-911c-fd97-1b78-e0f8c0141897@postgrespro.ru>
<15785.1536776055@sss.pgh.pa.us>
<20180926220419.lorxpb564gakdjkz@alap3.anarazel.de>
<20180926221814.el5nwmkez6zfmzbz@alap3.anarazel.de>
<14302.1538005507@sss.pgh.pa.us>
<20180926235821.zmpxqv66ob7v2ffi@alap3.anarazel.de>
<15882.1538007944@sss.pgh.pa.us>
<20180927004022.lfhffbj3roxzf5ca@alap3.anarazel.de>
<20180927005705.shbl3n5hq3t65n2j@alap3.anarazel.de>
>>>>> "Andres" == Andres Freund <andres@anarazel.de> writes:
Andres> Hm, stb's results just for floating point isn't bad. The above
Andres> numbers were for %f %f. But as the minimal usage would be about
Andres> the internal usage of dopr(), here's comparing %.*f:
Andres> snprintf time = 1324.87 ms total, 0.000264975 ms per iteration
Andres> pg time = 1434.57 ms total, 0.000286915 ms per iteration
Andres> stbsp time = 552.14 ms total, 0.000110428 ms per iteration
Hmm. We had a case recently on IRC where the performance of float8out
turned out to be the major bottleneck: a table of about 2.7 million rows
and ~70 float columns showed an overhead of ~66 seconds for doing COPY
as opposed to COPY BINARY (the actual problem report was that doing
"select * from table" from R was taking a minute+ longer than expected,
we got comparative timings for COPY just to narrow down causes).
That translates to approx. 0.00035 ms overhead (i.e. time(float8out) -
time(float8send)) per conversion (Linux server, hardware unknown).
That 66 seconds was the difference between 18s and 1m24s, so it wasn't a
small factor but totally dominated the query time.
--
Andrew (irc:RhodiumToad)
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To: pgsql-hackers@postgresql.org
Cc: andrew@tao11.riddles.org.uk, andres@anarazel.de, tgl@sss.pgh.pa.us, a.kuzmenkov@postgrespro.ru, pgsql-hackers@lists.postgresql.org
Subject: Re: Performance improvements for src/port/snprintf.c
In-Reply-To: <87r2hffwda.fsf@news-spur.riddles.org.uk>
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