Github user lemire commented on the pull request:
https://github.com/apache/spark/pull/9243#issuecomment-150947477
@srowen
Trying to compress something that is tiny and otherwise incompressible can
indeed lead to a storage increase of the order of 20%. That's credible. But
even if the 20% was in the other direction... that is, the compressed bitmaps
were 20% smaller, it would still not be worth it to compress in general. RAM
and storage are not that expensive in 2015. We use compressed bitmaps when
uncompressed ones are many times larger (at least 2x). Then you get both less
memory usage and faster processing speed.
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