From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-performance@postgresql.org, pgsql-hackers@postgresql.org, Michael Clemmons <glassresistor@gmail.com>
Cc: Hannu Krosing <hannu@2ndquadrant.com>
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Subject: Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)
Date: Mon, 28 Dec 2009 18:06:28 -0500
Message-ID: <3454.1262041588@sss.pgh.pa.us> (raw)
In-Reply-To: <200912282354.51892.andres@anarazel.de>
References: <4427a97a0912101235x3ade510blcc00d5ce9883c6b6@mail.gmail.com>
<4427a97a0912121236g4c06c562u221d638810ed2b6e@mail.gmail.com>
<200912122138.42404.andres@anarazel.de>
<200912282354.51892.andres@anarazel.de>
Andres Freund <andres@anarazel.de> writes:
> This speeds up CREATE DATABASE from ~9 seconds to something around 0.8s on my
> laptop. Still slower than with fsync off (~0.25) but quite a worthy
> improvement.
I can't help wondering whether that's real or some kind of
platform-specific artifact. I get numbers more like 3.5s (fsync off)
vs 4.5s (fsync on) on a machine where I believe the disks aren't lying
about write-complete. It makes sense that an fsync at the end would be
a little bit faster, because it would give the kernel some additional
freedom in scheduling the required I/O, but it isn't cutting the total
I/O required at all. So I find it really hard to believe a 10x speedup.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, andres@anarazel.de, glassresistor@gmail.com, hannu@2ndquadrant.com, scott.marlowe@gmail.com
Subject: Re: [HACKERS] Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)
In-Reply-To: <3454.1262041588@sss.pgh.pa.us>
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