[ben-schwen]

Closes #3330

library(data.table)
NN = 1e8
for (ngrp in c(8L, 1e6L)) {
  set.seed(304093)
  DT = data.table(grp = sample(ngrp, NN, TRUE),
                  V = rpois(NN, 10), key = 'grp')
  setDTthreads(12L)
  print(system.time(DT[ , mean(V), keyby = grp]))
  setDTthreads(6L)
  print(system.time(DT[ , mean(V), keyby = grp]))
  setDTthreads(1L)
  print(system.time(DT[ , mean(V), keyby = grp]))
}

I ran it for 10 rounds and took min / median / mean and max.

groups	threads	version	min	median	mean	max
8	1	1.11.6	0.85	0.86	0.87	0.89
8	1	1.12.1	0.69	0.71	0.73	0.89
8	1	master	1.82	1.92	1.99	2.41
8	1	PR	0.79	0.83	0.87	1.16
8	6	1.11.6	0.85	0.86	0.86	0.90
8	6	1.12.1	0.44	0.52	0.52	0.61
8	6	master	0.96	1.18	1.17	1.33
8	6	PR	0.83	0.91	0.92	1.04
8	12	1.11.6	0.84	0.85	0.87	1.05
8	12	1.12.1	0.50	0.56	0.57	0.64
8	12	master	0.97	1.09	1.15	1.64
8	12	PR	0.88	0.92	0.93	0.99
1e6	1	1.11.6	0.72	0.75	0.76	0.84
1e6	1	1.12.1	0.66	0.70	0.76	1.05
1e6	1	master	1.28	1.41	1.51	2.17
1e6	1	PR	0.82	0.88	0.99	1.58
1e6	6	1.11.6	0.70	0.70	0.71	0.76
1e6	6	1.12.1	0.25	0.29	0.28	0.31
1e6	6	master	0.61	0.65	0.67	0.76
1e6	6	PR	0.26	0.28	0.32	0.60
1e6	12	1.11.6	0.70	0.70	0.72	0.82
1e6	12	1.12.1	0.21	0.28	0.27	0.32
1e6	12	master	0.56	0.58	0.61	0.78
1e6	12	PR	0.24	0.27	0.27	0.33

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.08%. Comparing base (10bfd70) to head (fc67973).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7929      +/-   ##
==========================================
+ Coverage   99.02%   99.08%   +0.06%     
==========================================
  Files          88       88              
  Lines       17387    17418      +31     
==========================================
+ Hits        17217    17259      +42     
+ Misses        170      159      -11     

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[github-actions]

No obvious timing issues in HEAD=gforce_single_thread

Generated via commit 47da9f1

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	1 minutes and 57 seconds
Installing different package versions	8 minutes and 51 seconds
Running and plotting the test cases	3 minutes and 51 seconds

[jangorecki]

LGTM, amazing improvement!