Package edu.caltech.nanodb.functions

Class TableFunction

  • All Implemented Interfaces:
    java.lang.Cloneable
    public abstract class TableFunction
extends Function
    This is the base-class for all table-returning functions.

    • Constructor Summary

      Constructors 
      Constructor Description
      TableFunction()  

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      abstract void cleanUp()
      Perform any necessary clean up tasks.
      abstract PlanCost getCost()
      Returns the estimated cost of this plan node's operation.
      abstract Tuple getNextTuple()
      Gets the next tuple that fulfills the conditions for this plan node.
      abstract Schema getSchema()
      Returns the schema of the results that this node produces.
      abstract java.util.ArrayList<ColumnStats> getStats()
      Returns statistics (possibly estimated) describing the results that this plan node will produce.
      abstract void initialize()
      Does any initialization the node might need.
      abstract void prepare()
      This method is responsible for computing critical details about the plan node, such as the schema of the results that are produced, the estimated cost of evaluating the plan node (and its children), and statistics describing the results produced by the plan node.
      abstract java.util.List<OrderByExpression> resultsOrderedBy()
      If the results are ordered in some way, this method returns a collection of expressions specifying what columns or expressions the results are ordered by.

      • Methods inherited from class edu.caltech.nanodb.functions.Function

        clone

      • Methods inherited from class java.lang.Object

        equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • TableFunction

        public TableFunction()

    • Method Detail

      • resultsOrderedBy

        public abstract java.util.List<OrderByExpression> resultsOrderedBy()
        If the results are ordered in some way, this method returns a collection of expressions specifying what columns or expressions the results are ordered by. If the results are not ordered then this method may return either an empty list or a null value.

        When this method returns a list of ordering expressions, the order of the expressions themselves also matters. The entire set of results will be ordered by the first expression; rows with the same value for the first expression will be ordered by the second expression; etc.

        Returns:
        If the plan node produces ordered results, this will be a list of objects specifying the ordering. If the node doesn't produce ordered results then the return-value will either be an empty list or it will be null.

      • prepare

        public abstract void prepare()
        This method is responsible for computing critical details about the plan node, such as the schema of the results that are produced, the estimated cost of evaluating the plan node (and its children), and statistics describing the results produced by the plan node.

      • getSchema

        public abstract Schema getSchema()
        Returns the schema of the results that this node produces. Some nodes such as Select will not change the input schema but others, such as Project, Rename, and ThetaJoin, must change it.

        The schema is not computed until the prepare() method is called; until that point, this method will return null.

        Returns:
        the schema produced by this plan-node.

      • getCost

        public abstract PlanCost getCost()
        Returns the estimated cost of this plan node's operation. The estimate depends on which algorithm the node uses and the data it is working with.

        The cost is not computed until the prepare() method is called; until that point, this method will return null.

        Returns:
        an object containing various cost measures such as the worst-case number of disk accesses, the number of tuples produced, etc.

      • getStats

        public abstract java.util.ArrayList<ColumnStats> getStats()
        Returns statistics (possibly estimated) describing the results that this plan node will produce. Estimating statistics for output results is a very imprecise task, to say the least.

        These statistics are not computed until the prepare() method is called; until that point, this method will return null.

        Returns:
        statistics describing the results that will be produced by this plan-node.

      • initialize

        public abstract void initialize()
        Does any initialization the node might need. This could include resetting state variables or starting the node over from the beginning.

      • getNextTuple

        public abstract Tuple getNextTuple()
        Gets the next tuple that fulfills the conditions for this plan node. If the node has a child, it should call getNextTuple() on the child. If the node is a leaf, the tuple comes from some external source such as a table file, the network, etc.
        Returns:
        the next tuple to be generated by this plan, or null if the plan has finished generating plan nodes.

      • cleanUp

        public abstract void cleanUp()
        Perform any necessary clean up tasks. This should probably be called when we are done with this plan node.