net.sf.saffron.opt
Class RelSubset

java.lang.Object
  |
  +--net.sf.saffron.rel.SaffronRel
        |
        +--net.sf.saffron.opt.RelSubset

public class RelSubset

extends SaffronRel

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/net/sf/saffron/opt/RelSubset.java#5 $

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.

Field Summary

(package private) boolean	active whether findBestPlan is being called
(package private) SaffronRel	best best known plan
(package private) PlanCost	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 net.sf.saffron.rel.SaffronRel

cluster, digest, id, rowType

Constructor Summary

(package private)

RelSubset(VolcanoCluster cluster, RelSet set, CallingConvention convention)

Method Summary

(package private) void	add(SaffronRel rel) Add expression rel to this subset.
(package private) SaffronRel	buildCheapestPlan(SaffronPlanner 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.
PlanCost	computeSelfCost(SaffronPlanner planner) Returns the cost of this plan (not including children).
protected SaffronType	deriveRowType()
void	explain(PlanWriter pw)
CallingConvention	getConvention() Returns a value from CallingConvention.
SaffronRel[]	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, SaffronRel 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 net.sf.saffron.rel.SaffronRel

childrenAccept, getChildExps, getCluster, getCorrelVariable, getId, getInput, getOrCreateCorrelVariable, getQualifier, getQuery, getRelTypeName, getRows, getRowType, getTable, getVariablesStopped, implement, implementFieldAccess, isAccessTo, isDistinct, onRegister, recomputeDigest, register, registerCorrelVariable, replaceInput, setCorrelVariable, toString

Methods inherited from class java.lang.Object

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

Field Detail

parents

ArrayList parents

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

rels

ArrayList rels

convention

CallingConvention convention

bestCost

PlanCost bestCost

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

set

RelSet set

best

SaffronRel best

best known plan

active

boolean active

whether findBestPlan is being called

Constructor Detail

RelSubset

RelSubset(VolcanoCluster cluster,
          RelSet set,
          CallingConvention convention)

Method Detail

getConvention

public CallingConvention getConvention()

Description copied from class: SaffronRel

Returns a value from CallingConvention.

Overrides:

getConvention in class SaffronRel

getInputs

public SaffronRel[] 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 SaffronRel

getVariablesSet

public Set getVariablesSet()

getVariablesUsed

public Set getVariablesUsed()

clone

public Object clone()

An RelSet is its own clone.

Specified by:

clone in class SaffronRel

computeSelfCost

public PlanCost computeSelfCost(SaffronPlanner planner)

Description copied from class: SaffronRel

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

Overrides:

computeSelfCost in class SaffronRel

explain

public void explain(PlanWriter pw)

Overrides:

explain in class SaffronRel

computeDigest

protected String computeDigest()

Description copied from class: SaffronRel

Computes the digest. Does not modify this object.

Overrides:

computeDigest in class SaffronRel

deriveRowType

protected SaffronType deriveRowType()

Specified by:

deriveRowType in class SaffronRel

getParentRels

ArrayList getParentRels()

getParentSubsets

Set getParentSubsets()

getSet

RelSet getSet()

add

void add(SaffronRel rel)

Add expression rel to this subset.

buildCheapestPlan

SaffronRel buildCheapestPlan(SaffronPlanner planner)

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

propagateCostImprovements

private void propagateCostImprovements(VolcanoPlanner planner,
                                       SaffronRel rel)

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