Horton

Re: Spread checkpoint sync

Bruce Momjian <bruce@momjian.us>

View thread
From: Bruce Momjian <bruce@momjian.us>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Greg Smith <greg@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>, Ron Mayer <rm_pg@cheapcomplexdevices.com>, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Itagaki Takahiro <itagaki.takahiro@gmail.com>, pgsql-hackers@postgresql.org
Date: 2011-02-01T18:32:22Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add new buffers_backend_fsync field to pg_stat_bgwriter.

Kevin Grittner wrote:
> Robert Haas <robertmhaas@gmail.com> wrote:
>  
> > I also think Bruce's idea of calling fsync() on each relation just
> > *before* we start writing the pages from that relation might have
> > some merit.
>  
> What bothers me about that is that you may have a lot of the same
> dirty pages in the OS cache as the PostgreSQL cache, and you've just
> ensured that the OS will write those *twice*.  I'm pretty sure that
> the reason the aggressive background writer settings we use have not
> caused any noticeable increase in OS disk writes is that many
> PostgreSQL writes of the same buffer keep an OS buffer page from
> becoming stale enough to get flushed until PostgreSQL writes to it
> taper off.  Calling fsync() right before doing "one last push" of
> the data could be really pessimal for some workloads.

OK, maybe my idea needs to be adjusted and we should trigger an early
fsync if non-fsync writes are coming in for blocks _other_ than the ones
we already wrote for that checkpoint.

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

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