Re: [PATCH] Revert default wal_sync_method to fdatasync on Linux 2.6.33+

Josh Berkus wrote:
> On 12/6/10 6:13 PM, Tom Lane wrote:
> > Josh Berkus <josh@agliodbs.com> writes:
> >> OK, patch coming then.  Right now test_fsync aborts when O_DIRECT fails.
> >>  What should I have it do instead?
> > 
> > Report that it fails, and keep testing the other methods.
> 
> Patch attached.  Includes a fair amount of comment cleanup, since
> existing comments did not meet our current project standards.  Tests all
> 6 of the methods we support separately.
> 
> Some questions, though:
> 
> (1) Why are we doing the open_sync different-size write test?  AFAIK,
> this doesn't match any behavior which PostgreSQL has.

I added program output to explain this.

> (2) In this patch, I'm stepping down the number of loops which
> fsync_writethrough does by 90%.  The reason for that was that on the
> platforms where I tested writethrough (desktop machines), doing 10,000
> loops took 15-20 *minutes*, which seems hard on the user.  Would be easy
> to revert if you think it's a bad idea.
> 	Possibly auto-sizing the number of loops based on the first fsync test
> might be a good idea, but seems like going a bit too far.

I did not know why writethough we always be much slower than other sync
methods so I just reduced the loop count to 2k.

> (3) Should the multi-descriptor test be using writethrough on platforms
> which support it?

Thank you for your patch.  I have applied most of it, attached.  

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

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