[GitHub] [hudi] alexeykudinkin commented on a diff in pull request #5224: [HUDI-3739][Stacked on 5208] Fix handling of the `isNotNull` predicate in Data Skipping

[GitBox <gi...@apache.org>]

alexeykudinkin commented on code in PR #5224:
URL: https://github.com/apache/hudi/pull/5224#discussion_r843030033


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hudi-spark-datasource/hudi-spark-common/src/main/scala/org/apache/spark/sql/hudi/DataSkippingUtils.scala:
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@@ -211,10 +211,10 @@ object DataSkippingUtils extends Logging {
           .map(colName => GreaterThan(genColNumNullsExpr(colName), Literal(0)))
 
       // Filter "colA is not null"
-      // Translates to "colA_nullCount = 0" for index lookup
+      // Translates to "colA_nullCount < colA_valueCount" for index lookup
       case IsNotNull(attribute: AttributeReference) =>
         getTargetIndexedColumnName(attribute, indexSchema)
-          .map(colName => EqualTo(genColNumNullsExpr(colName), Literal(0)))
+          .map(colName => LessThan(genColNumNullsExpr(colName), genColValueCountExpr))

Review Comment:
   Ha! Great question. 
   
   The reason is logical fallacy: "colA is not null" != "there is no null in colA", instead it's "colA contains non-null" (you can check out some other expressions, there are many expressions in this list that carry such properties):
   
    - "is null" means that the column has to contain null values (ie `nullCount` > 0)
    - "is not null" means that the column has to contain non-null values (ie `nullCount` < `valueCount`)



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