Re: Perf Benchmarking and regression.

On Fri, May 13, 2016 at 1:43 PM, Andres Freund <andres@anarazel.de> wrote:
> On 2016-05-13 10:20:04 -0400, Robert Haas wrote:
>> On Fri, May 13, 2016 at 7:08 AM, Ashutosh Sharma <ashu.coek88@gmail.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.

You're just describing pgbench with a scale factor too large to fit in
shared_buffers.  I think it's unfair to paint that as some kind of
niche use case.

-- 
Robert Haas
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