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org.apache.spark.sql.catalyst.optimizer

MergeScalarSubqueries

object MergeScalarSubqueries extends Rule[LogicalPlan] with PredicateHelper

This rule tries to merge multiple non-correlated ScalarSubquerys to compute multiple scalar values once.

The process is the following: - While traversing through the plan each ScalarSubquery plan is tried to merge into the cache of already seen subquery plans. If merge is possible then cache is updated with the merged subquery plan, if not then the new subquery plan is added to the cache. During this first traversal each ScalarSubquery expression is replaced to a temporal ScalarSubqueryReference reference pointing to its cached version. The cache uses a flag to keep track of if a cache entry is a result of merging 2 or more plans, or it is a plan that was seen only once. Merged plans in the cache get a "Header", that contains the list of attributes form the scalar return value of a merged subquery. - A second traversal checks if there are merged subqueries in the cache and builds a WithCTE node from these queries. The CTERelationDef nodes contain the merged subquery in the following form: Project(Seq(CreateNamedStruct(name1, attribute1, ...) AS mergedValue), mergedSubqueryPlan) and the definitions are flagged that they host a subquery, that can return maximum one row. During the second traversal ScalarSubqueryReference expressions that pont to a merged subquery is either transformed to a GetStructField(ScalarSubquery(CTERelationRef(...))) expression or restored to the original ScalarSubquery.

Eg. the following query:

SELECT (SELECT avg(a) FROM t), (SELECT sum(b) FROM t)

is optimized from:

Optimized Logical Plan

Project [scalar-subquery#242 [] AS scalarsubquery()#253, scalar-subquery#243 [] AS scalarsubquery()#254L] : :- Aggregate [avg(a#244) AS avg(a)#247] : : +- Project [a#244] : : +- Relation default.t[a#244,b#245] parquet : +- Aggregate [sum(a#251) AS sum(a)#250L] : +- Project [a#251] : +- Relation default.t[a#251,b#252] parquet +- OneRowRelation

to:

Optimized Logical Plan

Project [scalar-subquery#242 [].avg(a) AS scalarsubquery()#253, scalar-subquery#243 [].sum(a) AS scalarsubquery()#254L] : :- Project [named_struct(avg(a), avg(a)#247, sum(a), sum(a)#250L) AS mergedValue#260] : : +- Aggregate [avg(a#244) AS avg(a)#247, sum(a#244) AS sum(a)#250L] : : +- Project [a#244] : : +- Relation default.t[a#244,b#245] parquet : +- Project [named_struct(avg(a), avg(a)#247, sum(a), sum(a)#250L) AS mergedValue#260] : +- Aggregate [avg(a#244) AS avg(a)#247, sum(a#244) AS sum(a)#250L] : +- Project [a#244] : +- Relation default.t[a#244,b#245] parquet +- OneRowRelation

Physical Plan

*(1) Project [Subquery scalar-subquery#242, [id=#125].avg(a) AS scalarsubquery()#253, ReusedSubquery Subquery scalar-subquery#242, [id=#125].sum(a) AS scalarsubquery()#254L] : :- Subquery scalar-subquery#242, [id=#125] : : +- *(2) Project [named_struct(avg(a), avg(a)#247, sum(a), sum(a)#250L) AS mergedValue#260] : : +- *(2) HashAggregate(keys=[], functions=[avg(a#244), sum(a#244)], output=[avg(a)#247, sum(a)#250L]) : : +- Exchange SinglePartition, ENSURE_REQUIREMENTS, [id=#120] : : +- *(1) HashAggregate(keys=[], functions=[partial_avg(a#244), partial_sum(a#244)], output=[sum#262, count#263L, sum#264L]) : : +- *(1) ColumnarToRow : : +- FileScan parquet default.t[a#244] ... : +- ReusedSubquery Subquery scalar-subquery#242, [id=#125] +- *(1) Scan OneRowRelation[]

Linear Supertypes
PredicateHelper, AliasHelper, Rule[LogicalPlan], Logging, SQLConfHelper, AnyRef, Any
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Inherited
  1. MergeScalarSubqueries
  2. PredicateHelper
  3. AliasHelper
  4. Rule
  5. Logging
  6. SQLConfHelper
  7. AnyRef
  8. Any
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Visibility
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Type Members

  1. case class Header(attributes: Seq[Attribute], plan: LogicalPlan, merged: Boolean) extends Product with Serializable

    An item in the cache of merged scalar subqueries.

    An item in the cache of merged scalar subqueries.

    attributes

    Attributes that form the struct scalar return value of a merged subquery.

    plan

    The plan of a merged scalar subquery.

    merged

    A flag to identify if this item is the result of merging subqueries. Please note that attributes.size == 1 doesn't always mean that the plan is not merged as there can be subqueries that are different (checkIdenticalPlans is false) due to an extra Project node in one of them. In that case attributes.size remains 1 after merging, but the merged flag becomes true.

Value Members

  1. final def !=(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  2. final def ##(): Int
    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  4. def apply(plan: LogicalPlan): LogicalPlan
    Definition Classes
    MergeScalarSubqueries → Rule
  5. final def asInstanceOf[T0]: T0
    Definition Classes
    Any
  6. def buildBalancedPredicate(expressions: Seq[Expression], op: (Expression, Expression) ⇒ Expression): Expression

    Builds a balanced output predicate in bottom up approach, by applying binary operator op pair by pair on input predicates exprs recursively.

    Builds a balanced output predicate in bottom up approach, by applying binary operator op pair by pair on input predicates exprs recursively. Example: exprs = [a, b, c, d], op = And, returns (a And b) And (c And d) exprs = [a, b, c, d, e, f], op = And, returns ((a And b) And (c And d)) And (e And f)

    Attributes
    protected
    Definition Classes
    PredicateHelper
  7. def canEvaluate(expr: Expression, plan: LogicalPlan): Boolean

    Returns true if expr can be evaluated using only the output of plan.

    Returns true if expr can be evaluated using only the output of plan. This method can be used to determine when it is acceptable to move expression evaluation within a query plan.

    For example consider a join between two relations R(a, b) and S(c, d).

    - canEvaluate(EqualTo(a,b), R) returns true - canEvaluate(EqualTo(a,c), R) returns false - canEvaluate(Literal(1), R) returns true as literals CAN be evaluated on any plan

    Attributes
    protected
    Definition Classes
    PredicateHelper
  8. def canEvaluateWithinJoin(expr: Expression): Boolean

    Returns true iff expr could be evaluated as a condition within join.

    Returns true iff expr could be evaluated as a condition within join.

    Attributes
    protected
    Definition Classes
    PredicateHelper
  9. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  10. def conf: SQLConf

    The active config object within the current scope.

    The active config object within the current scope. See SQLConf.get for more information.

    Definition Classes
    SQLConfHelper
  11. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  12. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  13. def extractPredicatesWithinOutputSet(condition: Expression, outputSet: AttributeSet): Option[Expression]

    Returns a filter that its reference is a subset of outputSet and it contains the maximum constraints from condition.

    Returns a filter that its reference is a subset of outputSet and it contains the maximum constraints from condition. This is used for predicate pushdown. When there is no such filter, None is returned.

    Attributes
    protected
    Definition Classes
    PredicateHelper
  14. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  15. def findExpressionAndTrackLineageDown(exp: Expression, plan: LogicalPlan): Option[(Expression, LogicalPlan)]

    Find the origin of where the input references of expression exp were scanned in the tree of plan, and if they originate from a single leaf node.

    Find the origin of where the input references of expression exp were scanned in the tree of plan, and if they originate from a single leaf node. Returns optional tuple with Expression, undoing any projections and aliasing that has been done along the way from plan to origin, and the origin LeafNode plan from which all the exp

    Definition Classes
    PredicateHelper
  16. def getAliasMap(exprs: Seq[NamedExpression]): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  17. def getAliasMap(plan: Aggregate): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  18. def getAliasMap(plan: Project): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  19. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  20. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  21. def initializeLogIfNecessary(isInterpreter: Boolean, silent: Boolean): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  22. def initializeLogIfNecessary(isInterpreter: Boolean): Unit
    Attributes
    protected
    Definition Classes
    Logging
  23. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  24. def isLikelySelective(e: Expression): Boolean

    Returns whether an expression is likely to be selective

    Returns whether an expression is likely to be selective

    Definition Classes
    PredicateHelper
  25. def isNullIntolerant(expr: Expression): Boolean
    Attributes
    protected
    Definition Classes
    PredicateHelper
  26. def isTraceEnabled(): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  27. def log: Logger
    Attributes
    protected
    Definition Classes
    Logging
  28. def logDebug(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  29. def logDebug(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  30. def logError(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  31. def logError(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  32. def logInfo(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  33. def logInfo(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  34. def logName: String
    Attributes
    protected
    Definition Classes
    Logging
  35. def logTrace(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  36. def logTrace(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  37. def logWarning(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  38. def logWarning(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  39. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  40. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  41. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  42. def outputWithNullability(output: Seq[Attribute], nonNullAttrExprIds: Seq[ExprId]): Seq[Attribute]
    Attributes
    protected
    Definition Classes
    PredicateHelper
  43. def replaceAlias(expr: Expression, aliasMap: AttributeMap[Alias]): Expression

    Replace all attributes, that reference an alias, with the aliased expression

    Replace all attributes, that reference an alias, with the aliased expression

    Attributes
    protected
    Definition Classes
    AliasHelper
  44. def replaceAliasButKeepName(expr: NamedExpression, aliasMap: AttributeMap[Alias]): NamedExpression

    Replace all attributes, that reference an alias, with the aliased expression, but keep the name of the outermost attribute.

    Replace all attributes, that reference an alias, with the aliased expression, but keep the name of the outermost attribute.

    Attributes
    protected
    Definition Classes
    AliasHelper
  45. lazy val ruleId: RuleId
    Attributes
    protected
    Definition Classes
    Rule
  46. val ruleName: String

    Name for this rule, automatically inferred based on class name.

    Name for this rule, automatically inferred based on class name.

    Definition Classes
    Rule
  47. def splitConjunctivePredicates(condition: Expression): Seq[Expression]
    Attributes
    protected
    Definition Classes
    PredicateHelper
  48. def splitDisjunctivePredicates(condition: Expression): Seq[Expression]
    Attributes
    protected
    Definition Classes
    PredicateHelper
  49. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  50. def toString(): String
    Definition Classes
    AnyRef → Any
  51. def trimAliases(e: Expression): Expression
    Attributes
    protected
    Definition Classes
    AliasHelper
  52. def trimNonTopLevelAliases[T <: Expression](e: T): T
    Attributes
    protected
    Definition Classes
    AliasHelper
  53. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  54. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  55. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()

Inherited from PredicateHelper

Inherited from AliasHelper

Inherited from Rule[LogicalPlan]

Inherited from Logging

Inherited from SQLConfHelper

Inherited from AnyRef

Inherited from Any

Ungrouped