[GitHub] [spark] HeartSaVioR commented on a diff in pull request #36073: [SPARK-38787] [SS] Replace found value with non-null element in the remaining list for key and remove remaining null elements from values in keyWithIndexToValue store for stream-stream joins

[GitBox]

HeartSaVioR commented on code in PR #36073:
URL: https://github.com/apache/spark/pull/36073#discussion_r843409388


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sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/state/SymmetricHashJoinStateManager.scala:
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@@ -272,12 +289,36 @@ class SymmetricHashJoinStateManager(
         if (index != numValues - 1) {
           val valuePairAtMaxIndex = keyWithIndexToValue.get(currentKey, 
numValues - 1)
           if (valuePairAtMaxIndex != null) {
+            // likely case where last element is non-null and we can simply 
swap with index
             keyWithIndexToValue.put(currentKey, index, 
valuePairAtMaxIndex.value,
               valuePairAtMaxIndex.matched)
           } else {
-            val projectedKey = getInternalRowOfKeyWithIndex(currentKey)
-            logWarning(s"`keyWithIndexToValue` returns a null value for index 
${numValues - 1} " +
-              s"at current key $projectedKey.")
+            // Find the rightmost non null index and swap values with that 
index,
+            // if index returned is not the same as the passed one
+            val nonNullIndex = getRightMostNonNullIndex(index + 
1).getOrElse(index)
+            if (nonNullIndex != index) {
+              val valuePair = keyWithIndexToValue.get(currentKey, nonNullIndex)
+              keyWithIndexToValue.put(currentKey, index, valuePair.value,
+                valuePair.matched)
+            }
+
+            // If nulls were found at the end, get the projected key and log a 
warning
+            // for the range of null indices.
+            if (nonNullIndex != numValues - 1) {
+              val projectedKey = getInternalRowOfKeyWithIndex(currentKey)
+              logWarning(s"`keyWithIndexToValue` returns a null value for 
indices " +
+                s"with range from startIndex=${nonNullIndex + 1} " +
+                s"and endIndex=${numValues - 1} " +
+                s"at currentKey=$projectedKey.")

Review Comment:
   We need to triage "who" we want to guard against seeing this. We will open 
source the code how to encode the grouping key anyway, so it is pretty trivial 
for almost everyone to decode the hash if they are basically programmers (and 
possibly attackers).



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