Fix flaky memory usage test by guaranteeing array size. #10114
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vyasr
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bug
shwina
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Jan 24, 2022
galipremsagar
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5 - Ready to Merge
Codecov Report
@@ Coverage Diff @@
## branch-22.04 #10114 +/- ##
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+ Coverage 10.37% 10.42% +0.04%
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Files 119 119
Lines 20149 20607 +458
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+ Hits 2091 2148 +57
- Misses 18058 18459 +401
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The test
test_dataframe.py::test_memory_usage_multiis currently flaky. In theory it can fail for any value of therowsparameter, but in practice we only observe failures for the smaller value of 10. The reason for this is that the data for theMultiIndexis being constructed by randomly sampling from an array of size 3, and for a sufficiently small sample (e.g. 10) the probability that selection will not actually include all three values (e.g. a sample of[0, 1, 1, 1, 0, 1, 1, 0, 0, 1]) is not vanishingly small and occurs with observable frequency. The resultingMultiIndexwill encode the levels for that column as a column with only two values, and as a result the column will occupy 8 fewer bytes (one 64 bit integer or float) less of space than expected. This PR changes that by always sampling without replacement from an array of the same length as the number of rows. I could also have fixed this problem by fixing a random seed that ensures that all the values are always sampled, but I made this change instead because 1) it more clearly conveys the intent, and 2) fixing a seed is a change that we should discuss and apply globally across all our tests.