From: Brad Nicholson <bnichols@ca.afilias.info>
To: Karl Denninger <karl@denninger.net>
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Greg Smith <greg@2ndquadrant.com>
Cc: Scott Carey <scott@richrelevance.com>
Cc: Michael March <mmarch@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Completely un-tuned Postgresql benchmark results: SSD vs desktop HDD
Date: Tue, 10 Aug 2010 14:54:12 -0400
Message-ID: <4C61A054.6080400@ca.afilias.info> (raw)
In-Reply-To: <4C619C90.3090005@denninger.net>
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<BAE01AAD-6C69-48C7-BD2E-77E463D49903@richrelevance.com>
<AANLkTi=km+H+mZ=yyx0_HTFZ-yU2sh85D+p5cs+ZcUSF@mail.gmail.com>
<A1640F99-A7C5-4F04-9A25-782C46BE7DAB@richrelevance.com>
<4C617C80.9080509@2ndquadrant.com>
<4C619300.3080400@ca.afilias.info>
<4C6196DB.8050307@denninger.net>
<AANLkTi=pehZj1Bb8KVusGykyEzWn__pif-87Tz2beJYj@mail.gmail.com>
<4C619C90.3090005@denninger.net>
On 8/10/2010 2:38 PM, Karl Denninger wrote:
> Scott Marlowe wrote:
>> On Tue, Aug 10, 2010 at 12:13 PM, Karl Denninger<karl@denninger.net> wrote:
>>
>>> ANY disk that says "write is complete" when it really is not is entirely
>>> unsuitable for ANY real database use. It is simply a matter of time
>>>
>>
>> What about read only slaves where there's a master with 100+spinning
>> hard drives "getting it right" and you need a half dozen or so read
>> slaves? I can imagine that being ok, as long as you don't restart a
>> server after a crash without checking on it.
>>
> A read-only slave isn't read-only, is it?
>
> I mean, c'mon - how does the data get there?
>
A valid case is a Slony replica if used for query offloading (not for
DR). It's considered a read-only subscriber from the perspective of
Slony as only Slony can modify the data (although you are technically
correct, it is not read only - controlled write may be more accurate).
In case of failure, a rebuild + resubscribe gets you back to the same
consistency. If you have high IO requirements, and don't have the
budget to rack up extra disk arrays to meet them, it could be an option.
--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.
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To: pgsql-performance@postgresql.org
Cc: bnichols@ca.afilias.info, karl@denninger.net, scott.marlowe@gmail.com, greg@2ndquadrant.com, scott@richrelevance.com, mmarch@gmail.com
Subject: Re: Completely un-tuned Postgresql benchmark results: SSD vs desktop HDD
In-Reply-To: <4C61A054.6080400@ca.afilias.info>
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