Re: POC: Cache data in GetSnapshotData()

On Sun, Nov 1, 2015 at 8:46 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:

> On 5/25/15 10:04 PM, Amit Kapila wrote:
>
>> On Tue, May 26, 2015 at 12:10 AM, Andres Freund <andres(at)anarazel(dot)de
>> <mailto:andres(at)anarazel(dot)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?
>

No. I think one has to study the impact of this patch on latest code
especially after commit-0e141c0f.

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