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:
Here, we can see that there is a gain of ~15% to ~38% at higher client count.
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 MacBook-Pro.