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.coe...@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-gcckryaqqtdu8kfe4n6h...@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.


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