Re: [HACKERS] Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

From: Andres Freund <andres(at)anarazel(dot)de>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <gsstark(at)mit(dot)edu>, pgsql-hackers(at)postgresql(dot)org, pgsql-performance(at)postgresql(dot)org, Michael Clemmons <glassresistor(at)gmail(dot)com>, Hannu Krosing <hannu(at)2ndquadrant(dot)com>, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Subject: Re: [HACKERS] Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)
Date: 2010-02-02 18:34:07
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On Tuesday 02 February 2010 19:14:40 Robert Haas wrote:
> On Tue, Feb 2, 2010 at 12:50 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Andres Freund <andres(at)anarazel(dot)de> writes:
> >> On Tuesday 02 February 2010 18:36:12 Robert Haas wrote:
> >>> I took a look at this patch today and I agree with Tom that
> >>> pg_fsync_start() is a very confusing name. I don't know what the
> >>> right name is, but this doesn't fsync so I don't think it shuld have
> >>> fsync in the name. Maybe something like pg_advise_abandon() or
> >>> pg_abandon_cache(). The current name is really wishful thinking:
> >>> you're hoping that it will make the kernel start the fsync, but it
> >>> might not. I think pg_start_data_flush() is similarly optimistic.
> >>
> >> What about: pg_fsync_prepare().
> >
> > prepare_for_fsync()?
> It still seems mis-descriptive to me. Couldn't the same routine be
> used simply to abandon undirtied data that we no longer care about
> caching?
For now it could - but it very well might be converted to sync_file_range or
similar, which would have different "sideeffects".

As the potential code duplication is rather small I would prefer to describe
the prime effect not the sideeffects...


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