cloud-fan commented on a change in pull request #32301:
URL: https://github.com/apache/spark/pull/32301#discussion_r622729279
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
##########
@@ -17,71 +17,148 @@
package org.apache.spark.sql.catalyst.optimizer
+import scala.collection.mutable
+
import org.apache.spark.sql.catalyst.expressions._
import org.apache.spark.sql.catalyst.plans.logical._
import org.apache.spark.sql.internal.SQLConf
import org.apache.spark.sql.types._
/**
- * This aims to handle a nested column aliasing pattern inside the
`ColumnPruning` optimizer rule.
- * If a project or its child references to nested fields, and not all the
fields
- * in a nested attribute are used, we can substitute them by alias attributes;
then a project
- * of the nested fields as aliases on the children of the child will be
created.
+ * This aims to handle a nested column aliasing pattern inside the
[[ColumnPruning]] optimizer rule.
+ * If:
+ * - A [[Project]] or its child references nested fields
+ * - Not all of the fields in a nested attribute are used
+ * Then:
+ * - Substitute the nested field references with alias attributes
+ * - Add grandchild [[Project]]s transforming the nested fields to aliases
+ *
+ * Example 1: Project
+ * ------------------
+ * Before:
+ * +- Project [concat_ws(s#0.a, s#0.b) AS concat_ws(s.a, s.b)#1]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [concat_ws(_gen_alias_2#2, _gen_alias_3#3) AS concat_ws(s.a,
s.b)#1]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _gen_alias_2#2, s#0.b AS _gen_alias_3#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * Example 2: Project above Filter
+ * -------------------------------
+ * Before:
+ * +- Project [s#0.a AS s.a#1]
+ * +- Filter (length(s#0.b) > 2)
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [_gen_alias_2#2 AS s.a#1]
+ * +- Filter (length(_gen_alias_3#3) > 2)
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _gen_alias_2#2, s#0.b AS _gen_alias_3#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * Example 3: Nested columns in nested columns
+ * -------------------------------------------
+ * Before:
+ * +- Project [s#0.a AS s.a#1, s#0.a.a1 AS s.a.a1#2]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- LocalRelation <empty>, [s#0]
+ * After:
+ * +- Project [_gen_alias_3#3 AS s.a#1, _gen_alias_3#3.name AS s.a.a1#2]
+ * +- GlobalLimit 5
+ * +- LocalLimit 5
+ * +- Project [s#0.a AS _gen_alias_3#3]
+ * +- LocalRelation <empty>, [s#0]
+ *
+ * The schema of the datasource relation will be pruned in the
[[SchemaPruning]] optimizer rule.
*/
object NestedColumnAliasing {
def unapply(plan: LogicalPlan): Option[LogicalPlan] = plan match {
/**
* This pattern is needed to support [[Filter]] plan cases like
- * [[Project]]->[[Filter]]->listed plan in `canProjectPushThrough` (e.g.,
[[Window]]).
- * The reason why we don't simply add [[Filter]] in
`canProjectPushThrough` is that
+ * [[Project]]->[[Filter]]->listed plan in [[canProjectPushThrough]]
(e.g., [[Window]]).
+ * The reason why we don't simply add [[Filter]] in
[[canProjectPushThrough]] is that
* the optimizer can hit an infinite loop during the
[[PushDownPredicates]] rule.
*/
- case Project(projectList, Filter(condition, child))
- if SQLConf.get.nestedSchemaPruningEnabled &&
canProjectPushThrough(child) =>
- val exprCandidatesToPrune = projectList ++ Seq(condition) ++
child.expressions
- getAliasSubMap(exprCandidatesToPrune,
child.producedAttributes.toSeq).map {
- case (nestedFieldToAlias, attrToAliases) =>
- NestedColumnAliasing.replaceToAliases(plan, nestedFieldToAlias,
attrToAliases)
- }
+ case Project(projectList, Filter(condition, child)) if
+ SQLConf.get.nestedSchemaPruningEnabled && canProjectPushThrough(child)
=>
+ rewritePlanIfSubsetFieldsUsed(
+ plan, projectList ++ Seq(condition) ++ child.expressions,
child.producedAttributes.toSeq)
- case Project(projectList, child)
- if SQLConf.get.nestedSchemaPruningEnabled &&
canProjectPushThrough(child) =>
- val exprCandidatesToPrune = projectList ++ child.expressions
- getAliasSubMap(exprCandidatesToPrune,
child.producedAttributes.toSeq).map {
- case (nestedFieldToAlias, attrToAliases) =>
- NestedColumnAliasing.replaceToAliases(plan, nestedFieldToAlias,
attrToAliases)
- }
+ case Project(projectList, child) if
+ SQLConf.get.nestedSchemaPruningEnabled && canProjectPushThrough(child)
=>
+ rewritePlanIfSubsetFieldsUsed(
+ plan, projectList ++ child.expressions, child.producedAttributes.toSeq)
case p if SQLConf.get.nestedSchemaPruningEnabled && canPruneOn(p) =>
- val exprCandidatesToPrune = p.expressions
- getAliasSubMap(exprCandidatesToPrune, p.producedAttributes.toSeq).map {
- case (nestedFieldToAlias, attrToAliases) =>
- NestedColumnAliasing.replaceToAliases(p, nestedFieldToAlias,
attrToAliases)
- }
+ rewritePlanIfSubsetFieldsUsed(
+ plan, p.expressions, p.producedAttributes.toSeq)
case _ => None
}
+ /**
+ * Rewrites a plan with aliases if only a subset of the nested fields are
used.
+ */
+ def rewritePlanIfSubsetFieldsUsed(
+ plan: LogicalPlan,
+ exprList: Seq[Expression],
+ exclusiveAttrs: Seq[Attribute]): Option[LogicalPlan] = {
+ val attrToExtractValues = getAttributeToExtractValues(exprList,
exclusiveAttrs)
+ if (attrToExtractValues.isEmpty) {
+ None
+ } else {
+ Some(rewritePlanWithAliases(plan, attrToExtractValues))
+ }
+ }
+
/**
* Replace nested columns to prune unused nested columns later.
*/
- private def replaceToAliases(
+ def rewritePlanWithAliases(
plan: LogicalPlan,
- nestedFieldToAlias: Map[ExtractValue, Alias],
- attrToAliases: Map[ExprId, Seq[Alias]]): LogicalPlan = plan match {
- case Project(projectList, child) =>
- Project(
- getNewProjectList(projectList, nestedFieldToAlias),
- replaceWithAliases(child, nestedFieldToAlias, attrToAliases))
-
- // The operators reaching here was already guarded by `canPruneOn`.
- case other =>
- replaceWithAliases(other, nestedFieldToAlias, attrToAliases)
+ attributeToExtractValues: Map[Attribute, Seq[ExtractValue]]):
LogicalPlan = {
+ // Each expression can contain multiple nested fields.
+ // Note that we keep the original names to deliver to parquet in a
case-sensitive way.
+ // A new alias is created for each nested field.
+ val nestedFieldToAlias = attributeToExtractValues.flatMap { case (_,
nestedFields) =>
+ nestedFields.map { f =>
+ val exprId = NamedExpression.newExprId
+ val fieldName = f match {
+ case g: GetStructField => g.extractFieldName
+ case g: GetArrayStructFields => g.field.name
+ }
+ f -> Alias(f, s"_extract_${fieldName}")(exprId, Seq.empty, None)
+ }
+ }
+
+ // A reference attribute can have multiple aliases for nested fields.
+ val attrToAliases = attributeToExtractValues.map { case (attr,
nestedFields) =>
+ attr.exprId -> nestedFields.map(nestedFieldToAlias)
Review comment:
this map lookup looks fragile as it use java `equals` not semantic
equals. how about
```
val attributeToAliasesExtractValues =
AttributeMap(attributeToExtractValues.map ...)
val nestedFieldToAlias = attributeToAliasesExtractValues.flatMap...
```
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