[GitHub] [spark] cloud-fan commented on a change in pull request #24598: [SPARK-27699][SQL] Partially push down disjunctive predicated in Parquet/ORC

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cloud-fan commented on a change in pull request #24598: [SPARK-27699][SQL] Partially push down disjunctive predicated in Parquet/ORC
URL: https://github.com/apache/spark/pull/24598#discussion_r284219728
 
 

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 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFilters.scala
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 @@ -527,11 +527,22 @@ private[parquet] class ParquetFilters(
         }
 
       case sources.Or(lhs, rhs) =>
+        // The Or predicate is convertible when both of its children can be pushed down.
+        // That is to say, if one/both of the children can be partially pushed down, the Or
+        // predicate can be partially pushed down as well.
+        //
+        // Here is an example used to explain the reason.
+        // Let's say we have
+        // (a1 AND a2) OR (b1 AND b2),
+        // a1 and b1 is convertible, while a2 and b2 is not.
+        // The predicate can be converted as
+        // (a1 OR b1) AND (a1 OR b2) AND (a2 OR b1) AND (a2 OR b2)
 
 Review comment:
   The conversion from `(a1 AND a2) OR (b1 AND b2)` to`(a1 OR b1) AND (a1 OR b2) AND (a2 OR b1) AND (a2 OR b2)` always works no matter it's a top level boolean expression or not.

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