Packages

object JoinReorderDP extends PredicateHelper with Logging

Reorder the joins using a dynamic programming algorithm. This implementation is based on the paper: Access Path Selection in a Relational Database Management System. http://www.inf.ed.ac.uk/teaching/courses/adbs/AccessPath.pdf

First we put all items (basic joined nodes) into level 0, then we build all two-way joins at level 1 from plans at level 0 (single items), then build all 3-way joins from plans at previous levels (two-way joins and single items), then 4-way joins ... etc, until we build all n-way joins and pick the best plan among them.

When building m-way joins, we only keep the best plan (with the lowest cost) for the same set of m items. E.g., for 3-way joins, we keep only the best plan for items {A, B, C} among plans (A J B) J C, (A J C) J B and (B J C) J A. We also prune cartesian product candidates when building a new plan if there exists no join condition involving references from both left and right. This pruning strategy significantly reduces the search space. E.g., given A J B J C J D with join conditions A.k1 = B.k1 and B.k2 = C.k2 and C.k3 = D.k3, plans maintained for each level are as follows: level 0: p({A}), p({B}), p({C}), p({D}) level 1: p({A, B}), p({B, C}), p({C, D}) level 2: p({A, B, C}), p({B, C, D}) level 3: p({A, B, C, D}) where p({A, B, C, D}) is the final output plan.

For cost evaluation, since physical costs for operators are not available currently, we use cardinalities and sizes to compute costs.

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Type Members

  1. case class JoinPlan(itemIds: Set[Int], plan: LogicalPlan, joinConds: Set[Expression], planCost: Cost) extends Product with Serializable

    Partial join order in a specific level.

    Partial join order in a specific level.

    itemIds

    Set of item ids participating in this partial plan.

    plan

    The plan tree with the lowest cost for these items found so far.

    joinConds

    Join conditions included in the plan.

    planCost

    The cost of this plan tree is the sum of costs of all intermediate joins.

  2. type JoinPlanMap = Map[Set[Int], JoinPlan]

    Map[set of item ids, join plan for these items]

Value Members

  1. final def !=(arg0: Any): Boolean
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  2. final def ##(): Int
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  3. final def ==(arg0: Any): Boolean
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  4. final def asInstanceOf[T0]: T0
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  5. 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
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    PredicateHelper
  6. 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.

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  7. def clone(): AnyRef
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  8. final def eq(arg0: AnyRef): Boolean
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  9. def equals(arg0: Any): Boolean
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  10. def finalize(): Unit
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  11. 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

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  12. final def getClass(): Class[_]
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  14. def initializeLogIfNecessary(isInterpreter: Boolean, silent: Boolean): Boolean
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  15. def initializeLogIfNecessary(isInterpreter: Boolean): Unit
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  16. final def isInstanceOf[T0]: Boolean
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  17. def isTraceEnabled(): Boolean
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  18. def log: Logger
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  19. def logDebug(msg: ⇒ String, throwable: Throwable): Unit
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  20. def logDebug(msg: ⇒ String): Unit
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  21. def logError(msg: ⇒ String, throwable: Throwable): Unit
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  22. def logError(msg: ⇒ String): Unit
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  23. def logInfo(msg: ⇒ String, throwable: Throwable): Unit
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  24. def logInfo(msg: ⇒ String): Unit
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  25. def logName: String
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  26. def logTrace(msg: ⇒ String, throwable: Throwable): Unit
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  27. def logTrace(msg: ⇒ String): Unit
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  28. def logWarning(msg: ⇒ String, throwable: Throwable): Unit
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  29. def logWarning(msg: ⇒ String): Unit
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  30. final def ne(arg0: AnyRef): Boolean
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  32. final def notifyAll(): Unit
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  33. def replaceAlias(condition: Expression, aliases: AttributeMap[Expression]): Expression
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  34. def search(conf: SQLConf, items: Seq[LogicalPlan], conditions: Set[Expression], output: Seq[Attribute]): LogicalPlan
  35. def splitConjunctivePredicates(condition: Expression): Seq[Expression]
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  36. def splitDisjunctivePredicates(condition: Expression): Seq[Expression]
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  37. final def synchronized[T0](arg0: ⇒ T0): T0
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