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Re: Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

From: david(at)lang(dot)hm
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, pgsql-performance(at)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org, Michael Clemmons <glassresistor(at)gmail(dot)com>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Subject: Re: Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)
Date: 2009-12-29 00:46:26
Message-ID: alpine.DEB.2.00.0912281645040.24130@asgard.lang.hm (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
On Tue, 29 Dec 2009, Andres Freund wrote:

> On Tuesday 29 December 2009 01:30:17 david(at)lang(dot)hm wrote:
>> On Tue, 29 Dec 2009, Greg Stark wrote:
>>> On Mon, Dec 28, 2009 at 10:54 PM, Andres Freund <andres(at)anarazel(dot)de>
> wrote:
>>>> fsync everything in that pass.
>>>> Including the directory - which was not done before and actually might
>>>> be necessary in some cases.
>>>
>>> Er. Yes. At least on ext4 this is pretty important. I wish it weren't,
>>> but it doesn't look like we're going to convince the ext4 developers
>>> they're crazy any day soon and it would really suck for a database
>>> created from a template to have files in it go missin.
>>
>> actually, as I understand it you need to do this on all filesystems except
>> ext3, and on ext3 fsync is horribly slow because it writes out
>> _everything_ that's pending, not just stuff related to the file you do the
>> fsync on.
> I dont think its all filesystems (ext2 should not be affected...), but generally
> youre right. At least jfs, xfs are affected as well.

ext2 definantly needs the fsync on the directory as well as the file 
(well, if the file metadata like size, change)

> Its btw not necessarily nearly-safe and slow on ext3 as well (data=writeback).

no, then it's just unsafe and slow ;-)

David Lang

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