Re: Perf Benchmarking and regression.

On 2016-06-08 23:00:15 -0400, Noah Misch wrote:
> On Sun, May 29, 2016 at 01:26:03AM -0400, Noah Misch wrote:
> > On Thu, May 12, 2016 at 10:49:06AM -0400, Robert Haas wrote:
> > > On Thu, May 12, 2016 at 8:39 AM, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> > > > Please find the test results for the following set of combinations taken at
> > > > 128 client counts:
> > > >
> > > > 1) Unpatched master, default *_flush_after :  TPS = 10925.882396
> > > >
> > > > 2) Unpatched master, *_flush_after=0 :  TPS = 18613.343529
> > > >
> > > > 3) That line removed with #if 0, default *_flush_after :  TPS = 9856.809278
> > > >
> > > > 4) That line removed with #if 0, *_flush_after=0 :  TPS = 18158.648023
> > > 
> > > I'm getting increasingly unhappy about the checkpoint flush control.
> > > I saw major regressions on my parallel COPY test, too:
> > > 
> > > http://www.postgresql.org/message-id/CA+TgmoYoUQf9cGcpgyGNgZQHcY-gCcKRyAqQtDU8KFE4N6HVkA@mail.gmail.com
> > > 
> > > That was a completely different machine (POWER7 instead of Intel,
> > > lousy disks instead of good ones) and a completely different workload.
> > > Considering these results, I think there's now plenty of evidence to
> > > suggest that this feature is going to be horrible for a large number
> > > of users.  A 45% regression on pgbench is horrible.  (Nobody wants to
> > > take even a 1% hit for snapshot too old, right?)  Sure, it might not
> > > be that way for every user on every Linux system, and I'm sure it
> > > performed well on the systems where Andres benchmarked it, or he
> > > wouldn't have committed it.  But our goal can't be to run well only on
> > > the newest hardware with the least-buggy kernel...
> > 
> > [This is a generic notification.]
> > 
> > The above-described topic is currently a PostgreSQL 9.6 open item.  Andres,
> > since you committed the patch believed to have created it, you own this open
> > item.  If some other commit is more relevant or if this does not belong as a
> > 9.6 open item, please let us know.  Otherwise, please observe the policy on
> > open item ownership[1] and send a status update within 72 hours of this
> > message.  Include a date for your subsequent status update.  Testers may
> > discover new open items at any time, and I want to plan to get them all fixed
> > well in advance of shipping 9.6rc1.  Consequently, I will appreciate your
> > efforts toward speedy resolution.  Thanks.
> > 
> > [1] http://www.postgresql.org/message-id/20160527025039.GA447393@tornado.leadboat.com
> 
> This PostgreSQL 9.6 open item is past due for your status update.  Kindly send
> a status update within 24 hours, and include a date for your subsequent status
> update.  Refer to the policy on open item ownership:
> http://www.postgresql.org/message-id/20160527025039.GA447393@tornado.leadboat.com

I'm writing a patch right now, planning to post it later today, commit
it tomorrow.

Greetings,

Andres Freund