[GitHub] [drill] paul-rogers commented on a change in pull request #1896: DRILL-7441: Fix issues with fillEmpties, offset vectors

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paul-rogers commented on a change in pull request #1896: DRILL-7441: Fix issues with fillEmpties, offset vectors
URL: https://github.com/apache/drill/pull/1896#discussion_r347010087
 
 

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 File path: exec/vector/src/main/codegen/templates/NullableValueVectors.java
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 @@ -844,29 +841,35 @@ public void generateTestData(int valueCount) {
 
     @Override
     public void reset() {
-      setCount = 0;
       <#if type.major = "VarLen">lastSet = -1;</#if>
     }
 
     <#if type.major = "VarLen">
     @VisibleForTesting
     public int getLastSet() { return lastSet; }
-    
+
     </#if>
+    @Override
+    public void setSetCount(int n) {
+      <#if type.major = "VarLen">lastSet = n - 1;</#if>
+    }
+    
     // For nullable vectors, exchanging buffers (done elsewhere)
     // requires also exchanging mutator state (done here.)
 
     @Override
     public void exchange(ValueVector.Mutator other) {
-      final Mutator target = (Mutator) other;
-      int temp = setCount;
-      setCount = target.setCount;
-      target.setCount = temp;
+      <#if type.major == "VarLen">
 
 Review comment:
   This is a bit subtle. The old code exchanged the `setCount` variable. But, it turned out that `setCount` was never actually used, so I removed it.
   
   However, this code contained a bug: it did not exchange the `lastSet` field, which is actually used. So, I added the code to exchange `lastSet`. But, `lastSet` is defined only for variable width types, where it is used to backfill the offset vectors.

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