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org.apache.spark.sql.catalyst.optimizer

DecorrelateInnerQuery

object DecorrelateInnerQuery extends PredicateHelper

Decorrelate the inner query by eliminating outer references and create domain joins. The implementation is based on the paper: Unnesting Arbitrary Queries by Thomas Neumann and Alfons Kemper. https://dl.gi.de/handle/20.500.12116/2418.

A correlated subquery can be viewed as a "dependent" nested loop join between the outer and the inner query. For each row produced by the outer query, we bind the OuterReferences in in the inner query with the corresponding values in the row, and then evaluate the inner query.

Dependent Join :- Outer Query +- Inner Query

If the OuterReferences are bound to the same value, the inner query will return the same result. Based on this, we can reduce the times to evaluate the inner query by first getting all distinct values of the OuterReferences.

Normal Join :- Outer Query +- Dependent Join :- Inner Query +- Distinct Aggregate (outer_ref1, outer_ref2, ...) +- Outer Query

The distinct aggregate of the outer references is called a "domain", and the dependent join between the inner query and the domain is called a "domain join". We need to push down the domain join through the inner query until there is no outer reference in the sub-tree and the domain join will turn into a normal join.

The decorrelation function returns a new query plan with optional placeholder DomainJoinss added and a list of join conditions with the outer query. DomainJoins need to be rewritten into actual inner join between the inner query sub-tree and the outer query.

E.g. decorrelate an inner query with equality predicates:

SELECT (SELECT MIN(b) FROM t1 WHERE t2.c = t1.a) FROM t2

Aggregate [] [min(b)] Aggregate [a] [min(b), a] +- Filter (outer(c) = a) => +- Relation [t1] +- Relation [t1]

Join conditions: [c = a]

E.g. decorrelate an inner query with non-equality predicates:

SELECT (SELECT MIN(b) FROM t1 WHERE t2.c > t1.a) FROM t2

Aggregate [] [min(b)] Aggregate [c'] [min(b), c'] +- Filter (outer(c) > a) => +- Filter (c' > a) +- Relation [t1] +- DomainJoin [c'] +- Relation [t1]

Join conditions: [c <=> c']

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  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(innerPlan: LogicalPlan, outerPlan: LogicalPlan, handleCountBug: Boolean = false): (LogicalPlan, Seq[Expression])
  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 canPullUpOverAgg(expression: Expression): Boolean

    Check if an expression can be pulled up over an Aggregate without changing the semantics of the plan.

    Check if an expression can be pulled up over an Aggregate without changing the semantics of the plan. The expression must be an equality predicate that guarantees one-to-one mapping between inner and outer attributes. For example: (a = outer(c)) -> true (a > outer(c)) -> false (a + b = outer(c)) -> false (a = outer(c) - b) -> false

  10. def clone(): AnyRef
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.CloneNotSupportedException]) @native()
  11. def deduplicate(innerPlan: LogicalPlan, conditions: Seq[Expression], outerOutputSet: AttributeSet): (LogicalPlan, Seq[Expression])

    Deduplicate the inner and the outer query attributes and return an aliased subquery plan and join conditions if duplicates are found.

    Deduplicate the inner and the outer query attributes and return an aliased subquery plan and join conditions if duplicates are found. Duplicated attributes can break the structural integrity when joining the inner and outer plan together.

  12. final def eq(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  13. def equals(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef → Any
  14. 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
  15. def finalize(): Unit
    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.Throwable])
  16. 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
  17. def getAliasMap(exprs: Seq[NamedExpression]): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  18. def getAliasMap(plan: Aggregate): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  19. def getAliasMap(plan: Project): AttributeMap[Alias]
    Attributes
    protected
    Definition Classes
    AliasHelper
  20. final def getClass(): Class[_ <: AnyRef]
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  21. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  22. def initializeLogIfNecessary(isInterpreter: Boolean, silent: Boolean): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  23. def initializeLogIfNecessary(isInterpreter: Boolean): Unit
    Attributes
    protected
    Definition Classes
    Logging
  24. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  25. 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
  26. def isNullIntolerant(expr: Expression): Boolean
    Attributes
    protected
    Definition Classes
    PredicateHelper
  27. def isTraceEnabled(): Boolean
    Attributes
    protected
    Definition Classes
    Logging
  28. def log: Logger
    Attributes
    protected
    Definition Classes
    Logging
  29. def logDebug(msg: => String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  30. def logDebug(msg: => String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  31. def logError(msg: => String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  32. def logError(msg: => String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  33. def logInfo(msg: => String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  34. def logInfo(msg: => String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  35. def logName: String
    Attributes
    protected
    Definition Classes
    Logging
  36. def logTrace(msg: => String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  37. def logTrace(msg: => String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  38. def logWarning(msg: => String, throwable: Throwable): Unit
    Attributes
    protected
    Definition Classes
    Logging
  39. def logWarning(msg: => String): Unit
    Attributes
    protected
    Definition Classes
    Logging
  40. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  41. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  42. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  43. def outputWithNullability(output: Seq[Attribute], nonNullAttrExprIds: Seq[ExprId]): Seq[Attribute]
    Attributes
    protected
    Definition Classes
    PredicateHelper
  44. def pushDomainConditionsThroughSemiAntiJoin(domainJoinConditions: Seq[Expression], join: Join): Seq[Expression]

    This is to handle INTERSECT/EXCEPT DISTINCT which are rewritten to left semi/anti join in ReplaceIntersectWithSemiJoin and ReplaceExceptWithAntiJoin.

    This is to handle INTERSECT/EXCEPT DISTINCT which are rewritten to left semi/anti join in ReplaceIntersectWithSemiJoin and ReplaceExceptWithAntiJoin.

    To rewrite the domain join on the right side, we need to remap the attributes in the domain join cond, using the mapping between left and right sides in the semi/anti join cond.

    After DecorrelateInnerQuery, the domain join conds reference the output names of the INTERSECT/EXCEPT, which come from the left side. When rewriting the DomainJoin in the right child, we need to remap the domain attribute names to account for the different names in the left vs right child, similar to pushDomainConditionsThroughSetOperation. But after the rewrite to semi/anti join is performed, we instead need to do the remapping based on the semi/anti join cond which contains equi-joins between the left and right outputs.

    Example: Take a query like: select * from t0 join lateral ( select a from t1 where b < t0.x intersect distinct select b from t2 where c < t0.y)

    over tables t0(x, y), t1(a), t2(b).

    Step 1 (this is the same as the Union case described above): After DecorrelateInnerQuery runs to introduce DomainJoins, we have outer table t0 with attributes [x#1, y#2] and the subquery is a Intersect where - the left side has DomainJoin [t0.x#4, t0.y#5] and output [t1.a#3, t0.x#4, t0.y#5] - the right side has DomainJoin [t0.x#7, t0.y#8] and output [t2.b#6, t0.x#7, t0.y#8] Here all the x and y attributes are from t0, but they are different instances from different joins of t0.

    The domain join conditions are x#4 <=> x#1 and y#5 <=> y#2, i.e. it joins the attributes from the original outer table with the attributes coming out of the DomainJoin of the left side, because the output of a set op uses the attribute names from the left side.

    Step 2: ReplaceIntersectWithSemiJoin runs and transforms the Intersect to Join LeftSemi, (((a#3 <=> b#6) AND (x#4 <=> x#7)) AND (y#5 <=> y#8)) with equi-joins between the left and right outputs. For EXCEPT DISTINCT the same thing happens but with anti join in ReplaceExceptWithAntiJoin.

    Step 3: rewriteDomainJoins runs, in which we arrive at this function, which uses the semijoin condition to construct the domain join cond remapping for the right side: x#7 <=> x#1 and y#8 <=> y#2. These new conds together with the original domain join cond are used to rewrite the DomainJoins.

    Note: This logic only applies to INTERSECT/EXCEPT DISTINCT. For INTERSECT/EXCEPT ALL, step 1 is the same but instead of step 2, RewriteIntersectAll or RewriteExceptAll replace the logical Intersect/Except operator with a combination of Union, Aggregate, and Generate. Then the DomainJoin conds will go through pushDomainConditionsThroughSetOperation, not this function.

  45. def pushDomainConditionsThroughSetOperation(conditions: Seq[Expression], setOp: LogicalPlan, child: LogicalPlan): Seq[Expression]

    Rewrites a domain join cond so that it can be pushed to the right side of a union/intersect/except operator.

    Rewrites a domain join cond so that it can be pushed to the right side of a union/intersect/except operator.

    Example: Take a query like: select * from t0 join lateral ( select a from t1 where b < t0.x union all select b from t2 where c < t0.y)

    over tables t0(x, y), t1(a), t2(b).

    Step 1: After DecorrelateInnerQuery runs to introduce DomainJoins, we have outer table t0 with attributes [x#1, y#2] and the subquery is a Union where - the left side has DomainJoin [t0.x#4, t0.y#5] and output [t1.a#3, t0.x#4, t0.y#5] - the right side has DomainJoin [t0.x#7, t0.y#8] and output [t2.b#6, t0.x#7, t0.y#8] Here all the x and y attributes are from t0, but they are different instances from different joins of t0.

    The domain join conditions are x#4 <=> x#1 and y#5 <=> y#2, i.e. it joins the attributes from the original outer table with the attributes coming out of the DomainJoin of the left side, because the output of a set op uses the attribute names from the left side.

    Step 2: rewriteDomainJoins runs, in which we arrive at this function. In this function, we construct the domain join conditions for the children of the Union. For the left side, those remain unchanged, while for the right side they are remapped to use the attribute names of the right-side DomainJoin: x#7 <=> x#1 and y#8 <=> y#2.

  46. 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
  47. 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
  48. def rewriteDomainJoins(outerPlan: LogicalPlan, innerPlan: LogicalPlan, conditions: Seq[Expression]): LogicalPlan

    Rewrite all DomainJoins in the inner query to actual joins with the outer query.

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

Inherited from PredicateHelper

Inherited from Logging

Inherited from AliasHelper

Inherited from AnyRef

Inherited from Any

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