Re: Performance degradation in commit 6150a1b0

On Wed, Mar 23, 2016 at 1:59 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
wrote:
>
> Hi All,
>
> I have been working on this issue for last few days trying to investigate
what could be the probable reasons for Performance degradation at commit
6150a1b0. After going through Andres patch for moving buffer I/O and
content lock out of Main Tranche, the following two things come into my
> mind.
>
> 1. Content Lock is no more used as a pointer in BufferDesc structure
instead it is included as LWLock structure. This basically increases the
overall structure size from 64bytes to 80 bytes. Just to investigate on
this, I have reverted the changes related to content lock from commit
6150a1b0 and taken at least 10 readings and with this change i can see that
the overall performance is similar to what it was observed earlier i.e.
before commit 6150a1b0.
>
> 2. Secondly, i can see that the BufferDesc structure padding is 64 bytes
however the PG CACHE LINE ALIGNMENT is 128 bytes. Also, after changing the
BufferDesc structure padding size to 128 bytes along with the changes
mentioned in above point #1, I see that the overall performance is again
similar to what is observed before commit 6150a1b0.
>
> Please have a look into the attached test report that contains the
performance test results for all the scenarios discussed above and let me
know your thoughts.
>

So this indicates that changing back content lock as LWLock* in BufferDesc
brings back the performance which indicates that increase in BufferDesc
size to more than 64bytes on this platform has caused regression. I think
it is worth trying the patch [1] as suggested by Andres as that will reduce
the size of BufferDesc which can bring back the performance. Can you once
try the same?

[1] -
http://www.postgresql.org/message-id/CAPpHfdsRoT1JmsnRnCCqpNZEU9vUT7TX6B-N1wyOuWWfhD6F+g@mail.gmail.com

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