razajafri commented on a change in pull request #31284:
URL: https://github.com/apache/spark/pull/31284#discussion_r563882773



##########
File path: 
sql/core/src/main/java/org/apache/spark/sql/execution/datasources/parquet/VectorizedColumnReader.java
##########
@@ -122,7 +123,24 @@ public VectorizedColumnReader(
     DictionaryPage dictionaryPage = pageReader.readDictionaryPage();
     if (dictionaryPage != null) {
       try {
-        this.dictionary = 
dictionaryPage.getEncoding().initDictionary(descriptor, dictionaryPage);
+        PrimitiveType primitiveType = descriptor.getPrimitiveType();
+        if (primitiveType.getOriginalType() == OriginalType.DECIMAL &&
+            primitiveType.getDecimalMetadata().getPrecision() <= 
Decimal.MAX_INT_DIGITS() &&
+            primitiveType.getPrimitiveTypeName() == 
PrimitiveType.PrimitiveTypeName.INT64) {
+          // We need to make sure that we initialize the right type for the 
dictionary otherwise
+          // Encoding#initDictionary will initialize it to 
PrimitiveTypeName.INT64 and
+          // WritableColumnVector will throw an exception when trying to 
decode to an Int when the
+          // dictionary is in fact initialized as Long

Review comment:
       I don't know for sure but 3rd party only base the output on parquet 
schema of the file. 
   The reason why we have to do this is because we are initializing the 
`WritableColumnVector` based on the sparkSchema and thus initializes it based 
on the precision and anything less than 10 precision is initialized to be 
backed by an Int even if the parquet schema has it stored as a long. 




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