Github user ron8hu commented on a diff in the pull request:
https://github.com/apache/spark/pull/16395#discussion_r95717900
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/statsEstimation/FilterEstimation.scala
---
@@ -0,0 +1,555 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.plans.logical.statsEstimation
+
+import scala.collection.immutable.{HashSet, Map}
+import scala.collection.mutable
+
+import org.apache.spark.internal.Logging
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.plans.logical._
+import org.apache.spark.sql.catalyst.util.DateTimeUtils
+import org.apache.spark.sql.types._
+import org.apache.spark.unsafe.types.UTF8String
+
+
+class FilterEstimation extends Logging {
+
+ /**
+ * We use a mutable colStats because we need to update the corresponding
ColumnStat
+ * for a column after we apply a predicate condition. For example, A
column c has
+ * [min, max] value as [0, 100]. In a range condition such as (c > 40
AND c <= 50),
+ * we need to set the column's [min, max] value to [40, 100] after we
evaluate the
+ * first condition c > 40. We need to set the column's [min, max] value
to [40, 50]
+ * after we evaluate the second condition c <= 50.
+ */
+ private var mutableColStats: mutable.Map[ExprId, ColumnStat] =
mutable.Map.empty
+
+ /**
+ * Returns an option of Statistics for a Filter logical plan node.
+ * For a given compound expression condition, this method computes
filter selectivity
+ * (or the percentage of rows meeting the filter condition), which
+ * is used to compute row count, size in bytes, and the updated
statistics after a given
+ * predicated is applied.
+ *
+ * @param plan a LogicalPlan node that must be an instance of Filter.
--- End diff --
We need this LogicalPlan so that we can access its child node's statistics
information.
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