Horton

Re: limiting hint bit I/O

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Cédric Villemain <cedric.villemain.debian@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Merlin Moncure <mmoncure@gmail.com>, Jim Nasby <jim@nasby.net>, Kevin Grittner <Kevin.Grittner@wicourts.gov>, Josh Berkus <josh@agliodbs.com>, pgsql-hackers Hackers <pgsql-hackers@postgresql.org>
Date: 2011-02-07T15:48:41Z
Lists: pgsql-hackers 
Robert Haas wrote:
> On Sat, Feb 5, 2011 at 4:31 PM, Bruce Momjian <bruce@momjian.us> wrote:
> > Uh, in this C comment:
> >
> > + ? ? ? ?* or not we want to take the time to write it. ?We allow up to 5% of
> > + ? ? ? ?* otherwise-not-dirty pages to be written due to hint bit changes,
> >
> > 5% of what? ?5% of all buffers? ?5% of all hint-bit-dirty ones? ?Can you
> > clarify this in the patch?
> 
> 5% of buffers that are hint-bit-dirty but not otherwise dirty.  ISTM
> that's exactly what the comment you just quoted says on its face, but
> I'm open to some other wording you want to propose.

How about:

	otherwise-not-dirty -> only-hint-bit-dirty

So 95% of your hint bit modificates are discarded if the pages is not
otherwise dirtied?  That seems pretty radical.

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

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