wesm edited a comment on pull request #7521:
URL: https://github.com/apache/arrow/pull/7521#issuecomment-647821487
Here's a benchmark run with gcc-8
```
-------------------------------------------------------------------------------
Benchmark Time CPU Iterations
UserCounters...
-------------------------------------------------------------------------------
BuildDictionary 2625315 ns 2625247 ns 271
null_percent=0.88889 1.4865GB/s
BuildStringDictionary 3475855 ns 3475854 ns 200 86.8577MB/s
UniqueInt64/0 9842842 ns 9842834 ns 71
null_percent=0 num_unique=1024 3.1749GB/s
UniqueInt64/1 10617685 ns 10617360 ns 66
null_percent=0.1 num_unique=1024 2.94329GB/s
UniqueInt64/2 12648447 ns 12648430 ns 59
null_percent=1 num_unique=1024 2.47066GB/s
UniqueInt64/3 15365202 ns 15365113 ns 43
null_percent=10 num_unique=1024 2.03383GB/s
UniqueInt64/4 5126936 ns 5126851 ns 128
null_percent=99 num_unique=1024 6.09536GB/s
UniqueInt64/5 1763829 ns 1763809 ns 400
null_percent=100 num_unique=1024 17.7173GB/s
UniqueInt64/6 10545960 ns 10545841 ns 67
null_percent=0 num_unique=10.24k 2.96325GB/s
UniqueInt64/7 11478529 ns 11478403 ns 61
null_percent=0.1 num_unique=10.24k 2.7225GB/s
UniqueInt64/8 12792912 ns 12792429 ns 54
null_percent=1 num_unique=10.24k 2.44285GB/s
UniqueInt64/9 16805938 ns 16805535 ns 44
null_percent=10 num_unique=10.24k 1.85951GB/s
UniqueInt64/10 5503266 ns 5503108 ns 114
null_percent=99 num_unique=10.24k 5.67861GB/s
UniqueInt64/11 1763742 ns 1763699 ns 392
null_percent=100 num_unique=10.24k 17.7184GB/s
UniqueString10bytes/0 44193582 ns 44191679 ns 16
null_percent=0 num_unique=1024 905.148MB/s
UniqueString10bytes/1 45022703 ns 45022263 ns 15
null_percent=0.1 num_unique=1024 888.449MB/s
UniqueString10bytes/2 47131705 ns 47130800 ns 15
null_percent=1 num_unique=1024 848.702MB/s
UniqueString10bytes/3 50106213 ns 50105455 ns 14
null_percent=10 num_unique=1024 798.316MB/s
UniqueString10bytes/4 15905586 ns 15905158 ns 43
null_percent=99 num_unique=1024 2.45596GB/s
UniqueString10bytes/5 12983446 ns 12983327 ns 55
null_percent=100 num_unique=1024 3.00867GB/s
UniqueString10bytes/6 62149404 ns 62148971 ns 11
null_percent=0 num_unique=10.24k 643.615MB/s
UniqueString10bytes/7 62707969 ns 62705282 ns 11
null_percent=0.1 num_unique=10.24k 637.905MB/s
UniqueString10bytes/8 65508665 ns 65508532 ns 10
null_percent=1 num_unique=10.24k 610.607MB/s
UniqueString10bytes/9 65766803 ns 65766094 ns 11
null_percent=10 num_unique=10.24k 608.216MB/s
UniqueString10bytes/10 16297990 ns 16298076 ns 43
null_percent=99 num_unique=10.24k 2.39676GB/s
UniqueString10bytes/11 13298987 ns 13298798 ns 54
null_percent=100 num_unique=10.24k 2.9373GB/s
UniqueString100bytes/0 94204048 ns 94200614 ns 7
null_percent=0 num_unique=1024 4.14674GB/s
UniqueString100bytes/1 95631478 ns 95630838 ns 7
null_percent=0.1 num_unique=1024 4.08472GB/s
UniqueString100bytes/2 96547756 ns 96546348 ns 7
null_percent=1 num_unique=1024 4.04598GB/s
UniqueString100bytes/3 91950796 ns 91949032 ns 8
null_percent=10 num_unique=1024 4.24828GB/s
UniqueString100bytes/4 17292562 ns 17291979 ns 42
null_percent=99 num_unique=1024 22.59GB/s
UniqueString100bytes/5 13096944 ns 13096809 ns 55
null_percent=100 num_unique=1024 29.826GB/s
UniqueString100bytes/6 196165738 ns 196161451 ns 4
null_percent=0 num_unique=10.24k 1.99134GB/s
UniqueString100bytes/7 198475556 ns 198475456 ns 4
null_percent=0.1 num_unique=10.24k 1.96813GB/s
UniqueString100bytes/8 199273625 ns 199270358 ns 3
null_percent=1 num_unique=10.24k 1.96028GB/s
UniqueString100bytes/9 189235180 ns 189232925 ns 4
null_percent=10 num_unique=10.24k 2.06425GB/s
UniqueString100bytes/10 18381309 ns 18381409 ns 36
null_percent=99 num_unique=10.24k 21.2511GB/s
UniqueString100bytes/11 13426102 ns 13426072 ns 51
null_percent=100 num_unique=10.24k 29.0945GB/s
UniqueUInt8/0 2239549 ns 2239561 ns 309
null_percent=0 num_unique=200 1.7442GB/s
UniqueUInt8/1 2687371 ns 2687349 ns 248
null_percent=0.1 num_unique=200 1.45357GB/s
UniqueUInt8/2 4244052 ns 4244058 ns 166
null_percent=1 num_unique=200 942.494MB/s
UniqueUInt8/3 7563076 ns 7563066 ns 94
null_percent=10 num_unique=200 528.886MB/s
UniqueUInt8/4 3313484 ns 3313447 ns 214
null_percent=99 num_unique=200 1.17891GB/s
UniqueUInt8/5 1711948 ns 1711947 ns 415
null_percent=100 num_unique=200 2.28176GB/s
```
Here is the % diff versus the baseline.
* Cases 1 and 7 are the mostly-not-null cases. This shows a 15-20% perf
improvement
* Cases 5 and 11 are the all-null cases.
* Case 4 and 10 are the 99% null cases
* The "BuildDictionary" case at the bottom with the perf regression is one
of the "worst case scenarios". 89% of the values are null and so we almost
never observe an all-null or all-not-null block. The use of `BitUtil::GetBit`
over BitmapReader causes this slightly regression since nearly every validity
bit must be checked separately. I don't think it's worth optimizing for this
case since the others are more empirically representative of real world data
```
benchmark baseline contender change %
regression
8 UniqueString100bytes/5 40.668 GiB/sec 272.392 GiB/sec 569.787
False
37 UniqueString10bytes/5 4.064 GiB/sec 27.207 GiB/sec 569.456
False
33 UniqueString10bytes/11 4.065 GiB/sec 27.062 GiB/sec 565.751
False
12 UniqueString100bytes/11 40.578 GiB/sec 264.909 GiB/sec 552.841
False
0 UniqueString10bytes/4 3.568 GiB/sec 9.051 GiB/sec 153.692
False
36 UniqueString100bytes/4 34.408 GiB/sec 83.010 GiB/sec 141.252
False
19 UniqueString10bytes/10 3.375 GiB/sec 7.891 GiB/sec 133.794
False
24 UniqueUInt8/1 677.981 MiB/sec 1.506 GiB/sec 127.435
False
5 UniqueString100bytes/10 30.775 GiB/sec 63.206 GiB/sec 105.381
False
27 UniqueUInt8/5 1000.163 MiB/sec 1.729 GiB/sec 76.989
False
13 UniqueUInt8/2 650.819 MiB/sec 846.372 MiB/sec 30.047
False
29 UniqueInt64/11 2.703 GiB/sec 3.409 GiB/sec 26.126
False
7 UniqueInt64/5 2.704 GiB/sec 3.404 GiB/sec 25.903
False
18 UniqueUInt8/4 932.926 MiB/sec 1.098 GiB/sec 20.535
False
23 UniqueInt64/1 1.681 GiB/sec 2.014 GiB/sec 19.840
False
21 UniqueInt64/7 1.628 GiB/sec 1.896 GiB/sec 16.476
False
31 UniqueInt64/2 1.658 GiB/sec 1.835 GiB/sec 10.651
False
20 UniqueString10bytes/7 612.647 MiB/sec 668.943 MiB/sec 9.189
False
16 UniqueInt64/3 1.386 GiB/sec 1.511 GiB/sec 9.053
False
38 UniqueString10bytes/8 601.259 MiB/sec 655.490 MiB/sec 9.019
False
1 UniqueUInt8/0 1.808 GiB/sec 1.963 GiB/sec 8.588
False
41 UniqueInt64/9 1.355 GiB/sec 1.458 GiB/sec 7.562
False
14 UniqueString10bytes/1 830.614 MiB/sec 886.336 MiB/sec 6.709
False
4 UniqueInt64/8 1.603 GiB/sec 1.703 GiB/sec 6.260
False
32 UniqueString10bytes/2 847.018 MiB/sec 884.017 MiB/sec 4.368
False
42 UniqueInt64/4 2.508 GiB/sec 2.600 GiB/sec 3.701
False
39 UniqueString10bytes/3 855.985 MiB/sec 886.914 MiB/sec 3.613
False
28 UniqueInt64/10 2.413 GiB/sec 2.494 GiB/sec 3.360
False
34 UniqueString100bytes/3 4.254 GiB/sec 4.369 GiB/sec 2.722
False
11 UniqueString100bytes/2 3.993 GiB/sec 4.094 GiB/sec 2.544
False
9 UniqueString10bytes/9 654.257 MiB/sec 668.714 MiB/sec 2.210
False
35 UniqueString10bytes/6 662.915 MiB/sec 676.832 MiB/sec 2.099
False
6 BuildStringDictionary 80.971 MiB/sec 81.753 MiB/sec 0.966
False
22 UniqueString100bytes/1 4.002 GiB/sec 4.033 GiB/sec 0.783
False
25 UniqueInt64/0 2.153 GiB/sec 2.168 GiB/sec 0.697
False
17 UniqueString10bytes/0 917.726 MiB/sec 918.783 MiB/sec 0.115
False
43 UniqueInt64/6 2.017 GiB/sec 2.016 GiB/sec -0.071
False
40 UniqueString100bytes/0 4.091 GiB/sec 4.086 GiB/sec -0.130
False
3 UniqueString100bytes/7 1.938 GiB/sec 1.909 GiB/sec -1.519
False
26 UniqueString100bytes/8 1.954 GiB/sec 1.897 GiB/sec -2.935
False
2 UniqueString100bytes/9 2.114 GiB/sec 2.034 GiB/sec -3.782
False
30 UniqueString100bytes/6 2.008 GiB/sec 1.895 GiB/sec -5.649
True
10 UniqueUInt8/3 474.468 MiB/sec 422.604 MiB/sec -10.931
True
15 BuildDictionary 1.776 GiB/sec 1.212 GiB/sec -31.742
True
```
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