org.eigenbase.relopt.volcano
Class RelSubset

java.lang.Object
  org.eigenbase.rel.AbstractRelNode
      org.eigenbase.relopt.volcano.RelSubset

All Implemented Interfaces:

Cloneable, RelNode

public class RelSubset
extends AbstractRelNode

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/dev/farrago/src/org/eigenbase/relopt/volcano/RelSubset.java#3 $

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) RelNode	best best known plan
(package private) RelOptCost	bestCost cost of best known plan (it may have improved since)
(package private) boolean	boosted Flag indicating whether this RelSubset's importance was artificially boosted.
(package private) List<RelNode>	parents List of the relational expressions for which this subset is an input.
(package private) List<RelNode>	rels The relational expressions in this subset.
(package private) RelSet	set The set this subset belongs to.
(package private) long	timestamp Timestamp for metadata validity
private static Logger	tracer

Fields inherited from class org.eigenbase.rel.AbstractRelNode

digest, id, rowType, traits

Fields inherited from interface org.eigenbase.rel.RelNode

emptyArray

Constructor Summary

RelSubset(RelOptCluster cluster, RelSet set, RelTraitSet traits)

Method Summary

(package private) void	add(RelNode rel) Adds expression rel to this subset.
(package private) RelNode	buildCheapestPlan(VolcanoPlanner planner) Recursively builds a tree consisting of the cheapest plan at each node.
RelSubset	clone() A RelSubSet is its own clone.
void	collectVariablesSet(Set<String> variableSet) Collects variables set by this expression.
void	collectVariablesUsed(Set<String> variableSet) Collects variables known to be used by this expression or its descendants.
protected String	computeDigest() Computes the digest.
RelOptCost	computeSelfCost(RelOptPlanner planner) Returns the cost of this plan (not including children).
protected RelDataType	deriveRowType()
void	explain(RelOptPlanWriter pw)
RelNode	getBest()
(package private) Collection<RelSubset>	getParentSubsets()
List<RelNode>	getRels() Returns the rel nodes in this rel subset.
double	getRows() Returns an estimate of the number of rows this relational expression will return.
(package private) RelSet	getSet()
Set<String>	getVariablesSet() There are no children, as such.
Set<String>	getVariablesUsed()
boolean	isDistinct() Returns whether the same value will not come out twice.
void	propagateBoostRemoval(VolcanoPlanner planner)
(package private) void	propagateCostImprovements(VolcanoPlanner planner, RelNode rel, Set<RelSubset> activeSet) 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 org.eigenbase.rel.AbstractRelNode

childrenAccept, cloneTraits, getChildExps, getCluster, getCollationList, getConvention, getCorrelVariable, getDescription, getDigest, getExpectedInputRowType, getId, getInput, getInputs, getOrCreateCorrelVariable, getQuery, getRelTypeName, getRowType, getTable, getTraits, getVariablesStopped, inheritTraitsFrom, isAccessTo, isValid, 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

tracer

private static final Logger tracer

parents

final List<RelNode> parents

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

rels

final List<RelNode> rels

The relational expressions in this subset.

bestCost

RelOptCost bestCost

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

set

final RelSet set

The set this subset belongs to.

best

RelNode best

best known plan

active

boolean active

whether findBestPlan is being called

timestamp

long timestamp

Timestamp for metadata validity

boosted

boolean boosted

Flag indicating whether this RelSubset's importance was artificially boosted.

Constructor Detail

RelSubset

RelSubset(RelOptCluster cluster,
          RelSet set,
          RelTraitSet traits)

Method Detail

getVariablesSet

public Set<String> getVariablesSet()

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

getVariablesUsed

public Set<String> getVariablesUsed()

getBest

public RelNode getBest()

clone

public RelSubset clone()

A RelSubSet is its own clone.

Specified by:

clone in interface RelNode

Specified by:

clone in class AbstractRelNode

Returns:

a clone of this RelNode

computeSelfCost

public RelOptCost computeSelfCost(RelOptPlanner planner)

Description copied from interface: RelNode

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

NOTE jvs 29-Mar-2006: Don't call this method directly. Instead, use RelMetadataQuery.getNonCumulativeCost(org.eigenbase.rel.RelNode), which gives plugins a chance to override the rel's default ideas about cost.

Specified by:

computeSelfCost in interface RelNode

Overrides:

computeSelfCost in class AbstractRelNode

getRows

public double getRows()

Description copied from interface: RelNode

Returns an estimate of the number of rows this relational expression will return.

NOTE jvs 29-Mar-2006: Don't call this method directly. Instead, use RelMetadataQuery.getRowCount(org.eigenbase.rel.RelNode), which gives plugins a chance to override the rel's default ideas about row count.

Specified by:

getRows in interface RelNode

Overrides:

getRows in class AbstractRelNode

explain

public void explain(RelOptPlanWriter pw)

Specified by:

explain in interface RelNode

Overrides:

explain in class AbstractRelNode

computeDigest

protected String computeDigest()

Description copied from class: AbstractRelNode

Computes the digest. Does not modify this object.

Overrides:

computeDigest in class AbstractRelNode

deriveRowType

protected RelDataType deriveRowType()

Overrides:

deriveRowType in class AbstractRelNode

isDistinct

public boolean isDistinct()

Description copied from interface: RelNode

Returns whether the same value will not come out twice. Default value is false, derived classes should override.

Specified by:

isDistinct in interface RelNode

Overrides:

isDistinct in class AbstractRelNode

getParentSubsets

Collection<RelSubset> getParentSubsets()

getSet

RelSet getSet()

add

void add(RelNode rel)

Adds expression rel to this subset.

buildCheapestPlan

RelNode buildCheapestPlan(VolcanoPlanner planner)

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

propagateCostImprovements

void propagateCostImprovements(VolcanoPlanner planner,
                               RelNode rel,
                               Set<RelSubset> activeSet)

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

Parameters:

planner - Planner

rel - Relational expression whose cost has improved

activeSet - Set of active subsets, for cycle detection

propagateBoostRemoval

public void propagateBoostRemoval(VolcanoPlanner planner)

collectVariablesUsed

public void collectVariablesUsed(Set<String> variableSet)

Description copied from interface: RelNode

Collects variables known to be used by this expression or its descendants. By default, no such information is available and must be derived by analyzing sub-expressions, but some optimizer implementations may insert special expressions which remember such information.

Specified by:

collectVariablesUsed in interface RelNode

Overrides:

collectVariablesUsed in class AbstractRelNode

Parameters:

variableSet - receives variables used

collectVariablesSet

public void collectVariablesSet(Set<String> variableSet)

Description copied from interface: RelNode

Collects variables set by this expression.

Specified by:

collectVariablesSet in interface RelNode

Overrides:

collectVariablesSet in class AbstractRelNode

Parameters:

variableSet - receives variables known to be set by

getRels

public List<RelNode> getRels()

Returns the rel nodes in this rel subset. All rels must have the same traits and are logically equivalent.

Returns:

all the rels in the subset