Re: Move PinBuffer and UnpinBuffer to atomics

On Sun, Apr 10, 2016 at 11:10 AM, Alexander Korotkov <
a(dot)korotkov(at)postgrespro(dot)ru> wrote:

> On Sun, Apr 10, 2016 at 7:26 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
>
>> On Sun, Apr 10, 2016 at 1:13 AM, Andres Freund <andres(at)anarazel(dot)de>
>> wrote:
>>
>>> On 2016-04-09 22:38:31 +0300, Alexander Korotkov wrote:
>>> > There are results with 5364b357 reverted.
>>>
>>>
>> What exactly is this test?
>> I think assuming it is a read-only -M prepared pgbench run where data
>> fits in shared buffers. However if you can share exact details, then I can
>> try the similar test.
>>
>
> Yes, the test is:
>
> pgbench -s 1000 -c $clients -j 100 -M prepared -S -T 300
> (shared_buffers=24GB)
>
>
>>
>>> Crazy that this has such a negative impact. Amit, can you reproduce
>>> that?
>>
>>
>> I will try it.
>>
>
> Good.
>

Okay, I have done some performance testing of read-only tests with
configuration suggested by you to see the impact

pin_unpin - latest version of pin unpin patch on top of HEAD.
pin_unpin_clog_32 - pin_unpin + change clog buffers to 32

Client_Count/Patch_ver 64 128
pin_unpin 330280 133586
pin_unpin_clog_32 388244 132388

This shows that at 64 client count, the performance is better with 32 clog
buffers. However, I think this is more attributed towards the fact that
contention seems to shifted to procarraylock as to an extent indicated in
Alexandar's mail. I will try once with cache the snapshot patch as well
and with clog buffers as 64.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com