alkis opened a new pull request, #40121:
URL: https://github.com/apache/spark/pull/40121
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### What changes were proposed in this pull request?
Reimplement `PercentileHeap` such that:
- the percentile value is always in the `topHeap`, this speeds up
`percentile` access
- change semantics such that percentile is defined as the equivalent of
sorting the array of all numbers and returning the nth element where `n =
floor(numElements * percentage)`
- rebalance the heaps more efficiently by checking which heap should grow
due to the new insertion and doing a rebalance based on target heap sizes
### Why are the changes needed?
`PercentileHeap` is heavy weight enough to cause scheduling delays if
inserted inside the scheduler loop.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Add more extensive unittests.
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