[GitHub] [spark] dongjoon-hyun commented on a change in pull request #26828: [SPARK-30198][Core] BytesToBytesMap does not grow internal long array as expected

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dongjoon-hyun commented on a change in pull request #26828: [SPARK-30198][Core] BytesToBytesMap does not grow internal long array as expected
URL: https://github.com/apache/spark/pull/26828#discussion_r356740416
 
 

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 File path: core/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java
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 @@ -741,7 +741,9 @@ public boolean append(Object kbase, long koff, int klen, Object vbase, long voff
         longArray.set(pos * 2 + 1, keyHashcode);
         isDefined = true;
 
-        if (numKeys >= growthThreshold && longArray.size() < MAX_CAPACITY) {
+        // We use two array entries per key, so the array size is twice the capacity.
+        // We should compare the current capacity of the array, instead of its size.
+        if (numKeys >= growthThreshold && longArray.size() / 2 < MAX_CAPACITY) {
 
 Review comment:
   @viirya . I agree your issue, but `longArray.size() / 2` might be too strict because we cap with `MAX_CAPACITY`. In other words, there is a room to grow still.
   ```
    // Allocate the new data structures
       allocate(Math.min(growthStrategy.nextCapacity(oldCapacity), MAX_CAPACITY));
   ```
   
   Can we have explicit test cases for these boundary conditions?

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