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Re: Anyone for SSDs?

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Daniel Loureiro <loureirorg(at)gmail(dot)com>, Vaibhav Kaushal <vaibhavkaushal123(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Anyone for SSDs?
Date: 2010-12-29 20:11:18
Message-ID: 201012292011.oBTKBIb14178@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
> > Of course if you do a full table scan because their are no better
> > options, then it scans sequentially.  But you have to scan the pages
> > in *some* order, and it is hard to see how something other than
> > sequential would be systematically better.
> 
> In fact, if sequential *isn't* the best order for reading the whole
> file, the filesystem has lost its marbles completely; because that is
> the order in which most files are read, so files ought to be laid out
> on disk (or whatever storage device) to be read most quickly that way.

Plus kernel read-ahead helps with sequential access too because the
kernel can guess the next blocks to be requested --- hard to do that
with random I/O.  SSD have fast access but still benefit from
read-ahead.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

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