On Tue, Feb 23, 2016 at 7:06 PM, Robert Haas <robertmh...@gmail.com> wrote:

> On Sun, Feb 21, 2016 at 7:45 PM, Amit Kapila <amit.kapil...@gmail.com>
> wrote:
>> I mean, my basic feeling is that I would not accept a 2-3% regression in
>>> the single client case to get a 10% speedup in the case where we have 128
>>> clients.
When I tried by running the pgbench first with patch and then with Head, I
see 1.2% performance increase with patch.  TPS with patch is 976 and with
Head it is 964. For 3, 30 mins TPS data, refer "Patch –
group_clog_update_v5" and before that "HEAD – Commit 481725c0"
in perf_write_clogcontrollock_data_v6.ods attached with this mail.

Nonetheless, I have observed that below new check has been added by the
patch which can effect single client performance.  So I have changed it
such that new check is done only when we there is actually a need of group
update which means when multiple clients tries to update clog at-a-time.

+       if (!InRecovery &&
+               all_trans_same_page &&
+               nsubxids < PGPROC_MAX_CACHED_SUBXIDS &&
+               !IsGXactActive())

> I understand your point.  I think to verify whether it is run-to-run
>> variation or an actual regression, I will re-run these tests on single
>> client multiple times and post the result.
> Perhaps you could also try it on a couple of different machines (e.g.
> MacBook Pro and a couple of different large servers).

Okay, I have tried latest patch (group_update_clog_v6.patch) on 2 different
big servers and then on Mac-Pro. The detailed data for various runs can be
found in attached document perf_write_clogcontrollock_data_v6.ods.  I have
taken the performance data for higher client-counts with somewhat larger
scale factor (1000) and data for median of same is as below:

M/c configuration
RAM - 500GB
8 sockets, 64 cores(Hyperthreaded128 threads total)

Non-default parameters
max_connections = 1000
checkpoint_timeout    =35min
maintenance_work_mem = 1GB
checkpoint_completion_target = 0.9
wal_buffers = 256MB

Client_Count/Patch_ver 1 8 64 128 256
HEAD 871 5090 17760 17616 13907
PATCH 900 5110 18331 20277 19263

Here, we can see that there is a gain of ~15% to ~38% at higher client

The attached document (perf_write_clogcontrollock_data_v6.ods) contains
data, mainly focussing on single client performance.  The data is for
multiple runs on different machines, so I thought it is better to present
in form of document rather than dumping everything in e-mail.  Do let me
know if there is any confusion in understanding/interpreting the data.

Thanks to Dilip Kumar for helping me in conducting test of this patch on

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

Attachment: group_update_clog_v6.patch
Description: Binary data

Attachment: perf_write_clogcontrollock_data_v6.ods
Description: application/vnd.oasis.opendocument.spreadsheet

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