Github user lemire commented on a diff in the pull request:
https://github.com/apache/spark/pull/9661#discussion_r44665632
--- Diff: core/src/main/scala/org/apache/spark/scheduler/MapStatus.scala ---
@@ -176,15 +179,17 @@ private[spark] object HighlyCompressedMapStatus {
// From a compression standpoint, it shouldn't matter whether we track
empty or non-empty
// blocks. From a performance standpoint, we benefit from tracking
empty blocks because
// we expect that there will be far fewer of them, so we will perform
fewer bitmap insertions.
+ val emptyBlocks = new RoaringBitmap()
+ val nonEmptyBlocks = new RoaringBitmap()
val totalNumBlocks = uncompressedSizes.length
- val emptyBlocks = new BitSet(totalNumBlocks)
while (i < totalNumBlocks) {
var size = uncompressedSizes(i)
if (size > 0) {
numNonEmptyBlocks += 1
+ nonEmptyBlocks.add(i)
totalSize += size
} else {
- emptyBlocks.set(i)
+ emptyBlocks.add(i)
}
--- End diff --
If you use ``RoaringBitmap`` and the RoaringBitmap objects are not expect
to change often after this loop, a call such as
``emptyBlocks.runOptimize();nonEmptyBlocks.runOptimize();`` might be warranted.
It should be checked.
Though it should not help, you can also investigate whether adding
``emptyBlocks.trim();nonEmptyBlocks.trim();`` can be helpful.
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