Date: Tue, 9 Dec 2014 15:43:37 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: intel s3500 -- hot stuff
Message-ID: <20141209204337.GC24488@momjian.us>
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On Mon, Dec  8, 2014 at 03:40:43PM -0600, Merlin Moncure wrote:
> >> Did not see consistent measurable gains > 256
> >> effective_io_concurrency.  Interesting that at setting of '2' (the
> >> lowest possible setting with the feature actually working) is
> >> pessimal.
> >
> > Very interesting.  When we added a per-tablespace random_page_cost,
> > there was a suggestion that we might want to add per-tablespace
> > effective_io_concurrency someday:
> 
> What I'd really like to see is to have effective_io_concurrency work
> on other types of scans.  It's clearly a barn burner on fast storage
> and perhaps the default should be something other than '1'.  Spinning
> storage is clearly dead and ssd seem to really benefit from the posix
> readhead api.

Well, the real question is knowing which blocks to request before
actually needing them.  With a bitmap scan, that is easy --- I am
unclear how to do it for other scans.  We already have kernel read-ahead
for sequential scans, and any index scan that hits multiple rows will
probably already be using a bitmap heap scan.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +


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