Re: Perf Benchmarking and regression.

On 2016-05-13 10:20:04 -0400, Robert Haas wrote:
> On Fri, May 13, 2016 at 7:08 AM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
> > Following are the performance results for read write test observed with
> > different numbers of "backend_flush_after".
> >
> > 1) backend_flush_after = 256kb (32*8kb), tps = 10841.178815
> > 2) backend_flush_after = 512kb (64*8kb), tps = 11098.702707
> > 3) backend_flush_after = 1MB (128*8kb), tps = 11434.964545
> > 4) backend_flush_after = 2MB (256*8kb), tps = 13477.089417
>
> So even at 2MB we don't come close to recovering all of the lost
> performance. Can you please test these three scenarios?
>
> 1. Default settings for *_flush_after
> 2. backend_flush_after=0, rest defaults
> 3. backend_flush_after=0, bgwriter_flush_after=0,
> wal_writer_flush_after=0, checkpoint_flush_after=0

4) 1) + a shared_buffers setting appropriate to the workload.

I just want to emphasize what we're discussing here is a bit of an
extreme setup. A workload that's bigger than shared buffers, but smaller
than the OS's cache size; with a noticeable likelihood of rewriting
individual OS page cache pages within 30s.

Greetings,

Andres Freund