jbimbert commented on a change in pull request #1298: DRILL-5796: Filter 
pruning for multi rowgroup parquet file
URL: https://github.com/apache/drill/pull/1298#discussion_r201930585
 
 

 ##########
 File path: 
exec/java-exec/src/main/java/org/apache/drill/exec/expr/stat/ParquetIsPredicate.java
 ##########
 @@ -62,70 +62,72 @@ private ParquetIsPredicate(LogicalExpression expr, 
BiPredicate<Statistics<C>, Ra
     return visitor.visitUnknown(this, value);
   }
 
-  @Override
-  public boolean canDrop(RangeExprEvaluator<C> evaluator) {
+  /**
+   * Apply the filter condition against the meta of the rowgroup.
+   */
+  public RowsMatch matches(RangeExprEvaluator<C> evaluator) {
     Statistics<C> exprStat = expr.accept(evaluator, null);
-    if (isNullOrEmpty(exprStat)) {
-      return false;
-    }
+    return isNullOrEmpty(exprStat) ? RowsMatch.SOME : 
predicate.apply(exprStat, evaluator);
+  }
 
-    return predicate.test(exprStat, evaluator);
+  /**
+   * After the applying of the filter against the statistics of the rowgroup, 
if the result is RowsMatch.ALL,
+   * then we still must know if the rowgroup contains some null values, 
because it can change the filter result.
+   * If it contains some null values, then we change the RowsMatch.ALL into 
RowsMatch.SOME, which sya that maybe
+   * some values (the null ones) should be disgarded.
+   */
+  private static RowsMatch checkNull(Statistics exprStat) {
+    return hasNoNulls(exprStat) ? RowsMatch.ALL : RowsMatch.SOME;
   }
 
   /**
    * IS NULL predicate.
    */
   private static <C extends Comparable<C>> LogicalExpression 
createIsNullPredicate(LogicalExpression expr) {
     return new ParquetIsPredicate<C>(expr,
-        //if there are no nulls  -> canDrop
-        (exprStat, evaluator) -> hasNoNulls(exprStat)) {
-      private final boolean isArray = isArray(expr);
-
-      private boolean isArray(LogicalExpression expression) {
-        if (expression instanceof TypedFieldExpr) {
-          TypedFieldExpr typedFieldExpr = (TypedFieldExpr) expression;
-          SchemaPath schemaPath = typedFieldExpr.getPath();
-          return schemaPath.isArray();
-        }
-        return false;
-      }
-
-      @Override
-      public boolean canDrop(RangeExprEvaluator<C> evaluator) {
+      (exprStat, evaluator) -> {
         // for arrays we are not able to define exact number of nulls
         // [1,2,3] vs [1,2] -> in second case 3 is absent and thus it's null 
but statistics shows no nulls
-        return !isArray && super.canDrop(evaluator);
-      }
-    };
+        if(expr instanceof TypedFieldExpr) {
+          TypedFieldExpr typedFieldExpr = (TypedFieldExpr) expr;
+          if (typedFieldExpr.getPath().isArray()) {
+            return RowsMatch.SOME;
+          }
+        }
+        if (hasNoNulls(exprStat)) {
+          return RowsMatch.NONE;
+        }
+        return isAllNulls(exprStat, evaluator.getRowCount()) ? RowsMatch.ALL : 
RowsMatch.SOME;
+      });
   }
 
   /**
    * IS NOT NULL predicate.
    */
   private static <C extends Comparable<C>> LogicalExpression 
createIsNotNullPredicate(LogicalExpression expr) {
     return new ParquetIsPredicate<C>(expr,
-        //if there are all nulls  -> canDrop
-        (exprStat, evaluator) -> isAllNulls(exprStat, evaluator.getRowCount())
+      (exprStat, evaluator) -> isAllNulls(exprStat, evaluator.getRowCount()) ? 
RowsMatch.NONE : checkNull(exprStat)
     );
   }
 
   /**
    * IS TRUE predicate.
    */
   private static LogicalExpression createIsTruePredicate(LogicalExpression 
expr) {
-    return new ParquetIsPredicate<Boolean>(expr, (exprStat, evaluator) ->
-        //if max value is not true or if there are all nulls  -> canDrop
-        isAllNulls(exprStat, evaluator.getRowCount()) || 
exprStat.hasNonNullValue() && !((BooleanStatistics) exprStat).getMax()
-    );
+    return new ParquetIsPredicate<Boolean>(expr, (exprStat, evaluator) -> {
+      if (isAllNulls(exprStat, evaluator.getRowCount()) || 
exprStat.hasNonNullValue() && !((BooleanStatistics)exprStat).getMax()) {
+        return RowsMatch.NONE;
+      }
+      return ((BooleanStatistics)exprStat).getMin() && 
((BooleanStatistics)exprStat).getMax() ? checkNull(exprStat) : RowsMatch.SOME;
+    });
   }
 
   /**
    * IS FALSE predicate.
    */
   private static LogicalExpression createIsFalsePredicate(LogicalExpression 
expr) {
     return new ParquetIsPredicate<Boolean>(expr, (exprStat, evaluator) ->
-        //if min value is not false or if there are all nulls  -> canDrop
-        isAllNulls(exprStat, evaluator.getRowCount()) || 
exprStat.hasNonNullValue() && ((BooleanStatistics) exprStat).getMin()
+      exprStat.hasNonNullValue() && ((BooleanStatistics)exprStat).getMin() || 
isAllNulls(exprStat, evaluator.getRowCount()) ? RowsMatch.NONE : 
checkNull(exprStat)
 
 Review comment:
   Yes. Necessary for test file blnTbl/0_0_2.parquet where we have ST:[min: 
false, max: true, num_nulls: 1]. In this case, the file is discarded, which is 
wrong since it contains 1 false.

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