saffron.opt
Class RelSubset

java.lang.Object
  |
  +--saffron.rel.Rel
        |
        +--saffron.opt.RelSubset

public class RelSubset

extends Rel

A RelSubset is set of expressions in a set which have the same calling convention. An expression may be in more than one sub-set of a set; the same expression is used.

Since:

16 December, 2001

Version:

$Id: //open/saffron/src/main/saffron/opt/RelSubset.java#8 $

Author:

jhyde

Nested Class Summary

(package private) class

RelSubset.CheapestPlanReplacer Visitor which walks over a tree of RelSets, replacing each node with the cheapest implementation of the expression.

Nested classes inherited from class saffron.rel.Rel

Field Summary

(package private) boolean	active whether findBestPlan is being called
(package private) Rel	best best known plan
(package private) Cost	bestCost cost of best known plan (it may have improved since)
(package private) CallingConvention	convention
(package private) ArrayList	parents List of the relational expressions for which this subset is an input.
(package private) ArrayList	rels
(package private) RelSet	set

Fields inherited from class saffron.rel.Rel

cluster, digest, id, rowType

Constructor Summary

(package private)

RelSubset(Cluster cluster, RelSet set, CallingConvention convention)

Method Summary

(package private) void	add(Rel rel) Add expression rel to this subset.
(package private) Rel	buildCheapestPlan(Planner planner) Recursively build a tree consisting of the cheapest plan at each node.
Object	clone() An RelSet is its own clone.
protected String	computeDigest() Computes the digest.
Cost	computeSelfCost(Planner planner) Returns the cost of this plan (not including children).
protected Type	deriveRowType()
void	explain(PlanWriter pw)
CallingConvention	getConvention() Returns a value from CallingConvention.
Rel[]	getInputs() There are no children, as such.
(package private) ArrayList	getParentRels()
(package private) Set	getParentSubsets()
(package private) RelSet	getSet()
Set	getVariablesSet()
Set	getVariablesUsed()
private void	propagateCostImprovements(VolcanoPlanner planner, Rel rel) Checks whether a relexp has made its subset cheaper, and if it so, recursively checks whether that subset's parents have gotten cheaper.

Methods inherited from class saffron.rel.Rel

childrenAccept, getChildExps, getCluster, getCorelVariable, getEnvironment, getId, getInput, getOrCreateCorelVariable, getParentEnv, getQualifier, getQuery, getRelTypeName, getRows, getRowType, getTable, getType, getVariablesStopped, implement, implementExp, implementExps, implementFieldAccess, implementSelf, isAccessTo, isDistinct, onRegister, recomputeDigest, register, registerCorelVariable, replaceInput, setCorelVariable, toString

Methods inherited from class java.lang.Object

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

Field Detail

set

RelSet set

convention

CallingConvention convention

rels

ArrayList rels

parents

ArrayList parents

List of the relational expressions for which this subset is an input.

bestCost

Cost bestCost

cost of best known plan (it may have improved since)

best

Rel best

best known plan

active

boolean active

whether findBestPlan is being called

Constructor Detail

RelSubset

RelSubset(Cluster cluster,
          RelSet set,
          CallingConvention convention)

Method Detail

getSet

RelSet getSet()

getParentRels

ArrayList getParentRels()

getParentSubsets

Set getParentSubsets()

add

void add(Rel rel)

Add expression rel to this subset.

propagateCostImprovements

private void propagateCostImprovements(VolcanoPlanner planner,
                                       Rel rel)

Checks whether a relexp has made its subset cheaper, and if it so, recursively checks whether that subset's parents have gotten cheaper.

clone

public Object clone()

An RelSet is its own clone.

Specified by:

clone in class Rel

computeDigest

protected String computeDigest()

Description copied from class: Rel

Computes the digest. Does not modify this object.

Overrides:

computeDigest in class Rel

getInputs

public Rel[] getInputs()

There are no children, as such. We throw an exception because you probably don't want to be walking over trees which contain RelSets.

Overrides:

getInputs in class Rel

deriveRowType

protected Type deriveRowType()

Specified by:

deriveRowType in class Rel

computeSelfCost

public Cost computeSelfCost(Planner planner)

Description copied from class: Rel

Returns the cost of this plan (not including children). The base implementation throws an error; derived classes should override.

Overrides:

computeSelfCost in class Rel

explain

public void explain(PlanWriter pw)

Overrides:

explain in class Rel

getConvention

public CallingConvention getConvention()

Description copied from class: Rel

Returns a value from CallingConvention.

Overrides:

getConvention in class Rel

getVariablesSet

public Set getVariablesSet()

getVariablesUsed

public Set getVariablesUsed()

buildCheapestPlan

Rel buildCheapestPlan(Planner planner)

Recursively build a tree consisting of the cheapest plan at each node.