To: Greg Stark <gsstark@mit.edu>
cc: Andres Freund <andres@anarazel.de>, pgsql-hackers@postgresql.org,
	pgsql-performance@postgresql.org,
	Michael Clemmons <glassresistor@gmail.com>,
	Hannu Krosing <hannu@2ndquadrant.com>,
	Scott Marlowe <scott.marlowe@gmail.com>
Subject: Re: [HACKERS] Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1
	ubuntu karmic slow createdb)
In-reply-to: <407d949e1001190652i43f4f276x6a485f375647219a@mail.gmail.com> 
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	<200912282354.51892.andres@anarazel.de>
	<200912282359.43979.andres@anarazel.de>
	<200912291930.50812.andres@anarazel.de>
	<407d949e1001180835m79ffe3e4w53e20ce2e1a58f2d@mail.gmail.com>
	<407d949e1001190652i43f4f276x6a485f375647219a@mail.gmail.com>
Comments: In-reply-to Greg Stark <gsstark@mit.edu>
	message dated "Tue, 19 Jan 2010 14:52:25 +0000"
Date: Tue, 19 Jan 2010 10:25:46 -0500
Message-ID: <9319.1263914746@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Greg Stark <gsstark@mit.edu> writes:
> 1) moved the posix_fadvise call to a new fd.c function
> pg_fsync_start(fd,offset,nbytes) which initiates an fsync without
> waiting on it. Currently it's only implemented with
> posix_fadvise(DONT_NEED) but I want to look into using sync_file_range
> in the future -- it looks like this call might be good enough for our
> checkpoints.

That function *seriously* needs documentation, in particular the fact
that it's a no-op on machines without the right kernel call.  The name
you've chosen is very bad for those semantics.  I'd pick something
else myself.  Maybe "pg_start_data_flush" or something like that?

Other than that quibble it seems basically sane.

			regards, tom lane