[GitHub] [spark] tomvanbussel commented on a change in pull request #29785: [SPARK-32901][CORE] Do not allocate memory while spilling UnsafeExternalSorter

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tomvanbussel commented on a change in pull request #29785:
URL: https://github.com/apache/spark/pull/29785#discussion_r490214568



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File path: core/src/main/java/org/apache/spark/util/collection/unsafe/sort/UnsafeExternalSorter.java
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@@ -339,29 +342,43 @@ public void cleanupResources() {
   private void growPointerArrayIfNecessary() throws IOException {
     assert(inMemSorter != null);
     if (!inMemSorter.hasSpaceForAnotherRecord()) {
+      if (inMemSorter.numRecords() <= 0) {

Review comment:
       We won't hit this block with the preallocated memory. Initially `inMemSorter.hasSpaceForAnotherRecord()` will be true, which can only become false after records have been inserted, at which point `inMemSorter.numRecords() <= 0` won't be true anymore.
   
   We could just check whether `inMemSorter` has memory allocated, but I tried to somewhat abstract the internals of `inMemSorter`. Not sure if that was the right decision though, given how tightly coupled `UnsafeExternalSorter` and `UnsafeInMemorySorter` currently are.




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