Packages

o

org.apache.spark.sql.catalyst.optimizer

MergeScalarSubqueries

object MergeScalarSubqueries extends Rule[LogicalPlan]

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
Rule[LogicalPlan], Logging, SQLConfHelper, AnyRef, Any
Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. MergeScalarSubqueries
  2. Rule
  3. Logging
  4. SQLConfHelper
  5. AnyRef
  6. Any
  1. Hide All
  2. Show All
Visibility
  1. Public
  2. All

Type Members

  1. case class Header(attributes: Seq[Attribute], plan: LogicalPlan, merged: Boolean, references: Set[Int]) 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.

    references

    A set of subquery indexes in the cache to track all (including transitive) nested subqueries.

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 clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  7. 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
  8. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  9. def equals(arg0: Any): Boolean
    Definition Classes
    AnyRef → Any
  10. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
  11. final def getClass(): Class[_]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  12. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  13. def initializeLogIfNecessary(isInterpreter: Boolean, silent: Boolean): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  14. def initializeLogIfNecessary(isInterpreter: Boolean): Unit
    Attributes
    protected
    Definition Classes
    Logging
  15. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  16. def isTraceEnabled(): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  17. def log: Logger
    Attributes
    protected
    Definition Classes
    Logging
  18. def logDebug(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  19. def logDebug(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  20. def logError(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  21. def logError(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  22. def logInfo(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  23. def logInfo(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  24. def logName: String
    Attributes
    protected
    Definition Classes
    Logging
  25. def logTrace(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  26. def logTrace(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  27. def logWarning(msg: ⇒ String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  28. def logWarning(msg: ⇒ String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  29. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  30. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  31. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  32. lazy val ruleId: RuleId
    Attributes
    protected
    Definition Classes
    Rule
  33. 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
  34. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  35. def toString(): String
    Definition Classes
    AnyRef → Any
  36. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  37. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  38. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()

Inherited from Rule[LogicalPlan]

Inherited from Logging

Inherited from SQLConfHelper

Inherited from AnyRef

Inherited from Any

Ungrouped