Message-ID: <4B698605.50506@anarazel.de>
Date: Wed, 03 Feb 2010 15:19:49 +0100
From: Andres Freund <andres@anarazel.de>
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To: Robert Haas <robertmhaas@gmail.com>
CC: Greg Stark <gsstark@mit.edu>, Tom Lane <tgl@sss.pgh.pa.us>,
	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)
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	<603c8f071002021014h4b489f44s9014377e1b38dbc7@mail.gmail.com>	
	<201002021934.18444.andres@anarazel.de>	
	<603c8f071002021106o5eef7b40r1ed21c9bd05251ec@mail.gmail.com>	
	<29129.1265139210@sss.pgh.pa.us>	
	<603c8f071002021145x1939c9e7hb2eedc8ae4dfe23e@mail.gmail.com>	
	<407d949e1002030353g522f1afev782a97fd755c5926@mail.gmail.com>
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On 02/03/10 14:42, Robert Haas wrote:
> On Wed, Feb 3, 2010 at 6:53 AM, Greg Stark<gsstark@mit.edu>  wrote:
>> On Tue, Feb 2, 2010 at 7:45 PM, Robert Haas<robertmhaas@gmail.com>  wrote:
>>> I think you're probably right, but it's not clear what the new name
>>> should be until we have a comment explaining what the function is
>>> responsible for.
>>
>> So I wrote some comments but wasn't going to repost the patch with the
>> unchanged name without explanation... But I think you're right though
>> I was looking at it the other way around. I want to have an API for a
>> two-stage sync and of course if I do that I'll comment it to explain
>> that clearly.
>>
>> The gist of the comments was that the function is preparing to fsync
>> to initiate the i/o early and allow the later fsync to fast -- but
>> also at the same time have the beneficial side-effect of avoiding
>> cache poisoning. It's not clear that the two are necessarily linked
>> though. Perhaps we need two separate apis, though it'll be hard to
>> keep them separate on all platforms.
>
> Well, maybe we should start with a discussion of what kernel calls
> you're aware of on different platforms and then we could try to put an
> API around it.
In linux there is sync_file_range. On newer Posixish systems one can 
emulate that with mmap() and msync() (in batches obviously).

No idea about windows.

Andres