Github user kiszk commented on the issue: https://github.com/apache/spark/pull/19518 I created and ran another synthetic benchmark program for comparing flat global variables, inner global variables, and array. In summary, the followings are performance results (**small number is better**). - 0.65: flat global variables - 0.91: inner global variables - 1: array WDYT? Any comments are very appreciated. Here are [Test.java](https://gist.github.com/kiszk/63c2829488cb777d7ca78d45d20c021f) and [myInsntance.py](https://gist.github.com/kiszk/049a62f5d1259481c400a86299bd0228) that I used. ``` $ cat /proc/cpuinfo | grep "model name" | uniq model name : Intel(R) Xeon(R) CPU E5-2667 v3 @ 3.20GHz $ java -version openjdk version "1.8.0_131" OpenJDK Runtime Environment (build 1.8.0_131-8u131-b11-2ubuntu1.16.04.3-b11) OpenJDK 64-Bit Server VM (build 25.131-b11, mixed mode) $ python myInstance.py > MyInstance.java && javac Test.java && java Test Result(us): Array 0: 462848.969 1: 461978.693 2: 463174.459 3: 461422.763 4: 460563.915 5: 460112.262 6: 460059.957 7: 460376.230 8: 460245.445 9: 460308.775 10: 460154.955 11: 460005.629 12: 460330.584 13: 460277.612 14: 460181.360 15: 460168.843 16: 459790.137 17: 460248.481 18: 460344.471 19: 460084.529 20: 459987.263 21: 459961.639 22: 459952.447 23: 460128.518 24: 460025.783 25: 459874.303 26: 459932.685 27: 460065.736 28: 459954.526 29: 459972.679 BEST: 459790.137000, AVG: 460417.788 Result(us): InnerVars 0: 421013.480 1: 420279.235 2: 419366.157 3: 421015.934 4: 419540.049 5: 420316.650 6: 419816.612 7: 420211.140 8: 420215.864 9: 421104.657 10: 421836.430 11: 420866.894 12: 421457.850 13: 421734.506 14: 420796.010 15: 419832.910 16: 420012.167 17: 420821.800 18: 420962.178 19: 421981.676 20: 421721.257 21: 419996.594 22: 419742.884 23: 420158.066 24: 420156.773 25: 420325.231 26: 420966.914 27: 420787.147 28: 420296.789 29: 420520.843 BEST: 419366.157, AVG: 420595.157 Result(us): Vars 0: 343490.797 1: 342849.079 2: 341990.967 3: 342844.044 4: 343484.681 5: 342586.419 6: 342468.883 7: 343113.300 8: 343516.875 9: 343002.395 10: 341499.538 11: 342192.102 12: 341847.383 13: 342533.215 14: 341376.556 15: 342018.111 16: 341316.445 17: 342043.378 18: 341969.932 19: 343415.854 20: 343103.133 21: 342084.686 22: 341555.293 23: 342984.355 24: 342302.336 25: 341994.372 26: 342475.639 27: 342281.214 28: 342205.175 29: 342462.032 BEST: 341316.445, AVG: 342433.606 ```
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