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Message-ID: <4BABD400.1000807@gmail.com>
Date: Thu, 25 Mar 2010 22:22:08 +0100
From: Yeb Havinga <yebhavinga@gmail.com>
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To: Scott Marlowe <scott.marlowe@gmail.com>
CC: Pierre C <lists@peufeu.com>, James Mansion <james@mansionfamily.plus.com>,
	Hannu Krosing <hannu@2ndquadrant.com>, Greg Smith <greg@2ndquadrant.com>,
	Tom Lane <tgl@sss.pgh.pa.us>, "Ross J. Reedstrom" <reedstrm@rice.edu>,
	pgsql-performance@postgresql.org
Subject: Re: mysql to postgresql, performance questions
References: <4BA23936.2030507@gmail.com> <4BA596D2.4050406@squeakycode.net>	
	<20100323185232.GD6662@rice.edu> <5342.1269372121@sss.pgh.pa.us>	
	<4BA934B9.9070401@2ndquadrant.com> <4BA9D39B.6020103@gmail.com>	
	<1269421198.11473.50.camel@hvost>	
	<4BABC1E0.7010607@mansionfamily.plus.com>	
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	<dcc563d11003251338m1369b4efh2efa600c9c8fe7dd@mail.gmail.com>
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Scott Marlowe wrote:
> On Thu, Mar 25, 2010 at 2:29 PM, Pierre C <lists@peufeu.com> wrote:
>   
>>> Hannu Krosing wrote:
>>>       
>>>> Pulling the plug should not corrupt a postgreSQL database, unless it was
>>>> using disks which lie about write caching.
>>>>
>>>>         
>>> Didn't we recently put the old wife's 'the disks lied' tale to bed in
>>> favour of actually admiting that some well known filesystems and saftware
>>> raid systems have had trouble with their write barriers?
>>>       
>> I put a cheap UPS on the home server (which uses Software RAID) precisely
>> because I don't really trust that stuff, and there is also the RAID5 write
>> hole... and maybe the RAID1 write hole too... and installing a UPS takes
>> less time that actually figuring out if the system is power-loss-safe.
>>     
>
> Very true, a UPS might not cover every possible failure mode, but it
> sure takes care of an aweful lot of the common ones.
>   
Yeah, but the original post was about mythtv boxes, which usually do not 
have upses. My suggestion about proper setup of the wal was based on 
some experience of my own. What I did was probably the fastest path to 
corrupt database files: diskless mythtv box that booted from the 
fileserver at the attic (with ups btw), but I was too lazy (after x days 
of lirc / xorg / ivtv / rtc / xmltv etc work) to move the default 
configured mysql database from the mythtv box (with root filesystem and 
also mysql on the nfs mount) to a mysql running on the fileserver 
itself. On top of that I had nfs mounted async for speed. Really after x 
days of configuration to get things running (my wife thinks it's hobby 
time but it really isn't) all that is on your mind is: it works good 
enough? fine, will iron out non essential things when they pop up and if 
the db becomes corrupt, I had database backups. In the end I had a few 
times a corrupt table that was always easily repaired with the 
mysqlcheck tool.

Based on this experience I do not think that reliability alone will 
convince mythtv developers/users to switch to postgresql, and besides 
that as a developer and user myself, it's always in a way funny to see 
how creative people can finding ways to not properly use (your) software ;-)

regards,
Yeb Havinga