Re: POC: Cache data in GetSnapshotData()

On 5/25/15 10:04 PM, Amit Kapila wrote:

On Tue, May 26, 2015 at 12:10 AM, Andres Freund <andres@anarazel.de

<mailto:andres@anarazel.de>> wrote:
 >
 > On 2015-05-20 19:56:39 +0530, Amit Kapila wrote:
 > > I have done some tests with this patch to see the benefit with
 > > and it seems to me this patch helps in reducing the contention
 > > around ProcArrayLock, though the increase in TPS (in tpc-b tests
 > > is around 2~4%) is not very high.
 > >
 > > pgbench (TPC-B test)
 > > ./pgbench -c 64 -j 64 -T 1200 -M prepared postgres
 >
 > Hm, so it's a read mostly test.

Write not *Read* mostly.

 > I probably not that badly contended on
 > the snapshot acquisition itself. I'd guess a 80/20 read/write mix or so
 > would be more interesting for the cases where we hit this really bad.
 >

Yes 80/20 read/write mix will be good test to test this patch and I think
such a load is used by many applications (Such a load is quite common
in telecom especially their billing related applications) and currently
we don't
have such a test handy to measure performance.

On a side note, I think it would be good if we can add such a test to
pgbench or may be use some test which adheres to TPC-C specification.
Infact, I remember [1] people posting test results with such a workload
showing ProcArrayLock as contention.


[1] -
http://www.postgresql.org/message-id/E8870A2F6A4B1045B1C292B77EAB207C77069A80@SZXEMA501-MBX.china.huawei.com

Anything happen with this?