Subject: Re: Completely un-tuned Postgresql benchmark results:
	SSD vs desktop HDD
From: Jeff Davis <pgsql@j-davis.com>
To: Scott Carey <scott@richrelevance.com>
Cc: Michael March <mmarch@gmail.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
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Date: Mon, 09 Aug 2010 15:41:59 -0700
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On Mon, 2010-08-09 at 09:49 -0700, Scott Carey wrote:
> Also, the amount of data at risk in a power loss varies between
> drives.  For Intel's drives, its a small chunk of data ( < 256K).  For
> some other drives, the cache can be over 30MB of outstanding writes.
> For some workloads this is acceptable -- not every application is
> doing financial transactions.   Not every part of the system needs to
> be on an SSD either -- the WAL, and various table spaces can all have
> different data integrity and performance requirements.

I don't think it makes sense to speak about the data integrity of a
drive in terms of the amount of data at risk, especially with a DBMS.
Depending on which 256K you lose, you might as well lose your entire
database.

That may be an exaggeration, but the point is that it's not as simple as
"this drive is only risking 256K data loss per outage".

Regards,
	Jeff Davis