org.apache.tajo.plan.rewrite.rules

Class ProjectionPushDownRule.TargetListManager

java.lang.Object

org.apache.tajo.plan.rewrite.rules.ProjectionPushDownRule.TargetListManager

Enclosing class:

ProjectionPushDownRule

public static class ProjectionPushDownRule.TargetListManager
extends Object

What is TargetListManager?

It manages all expressions used in a query block, and their reference names. TargetListManager provides a way to find an expression by a reference name. It keeps a set of expressions, and one or more reference names can point to the same expression. Also, TargetListManager keeps the evaluation state of each expression. The evaluation state is a boolean state to indicate whether the expression was evaluated in descendant node or not. If an expression is evaluated, the evaluation state is changed to TRUE. It also means that the expression can be referred by an column reference instead of evaluating the expression. Consider an example query: SELECT sum(l_orderkey + 1) from lineitem where l_partkey > 1; In this case, an expression sum(l_orderkey + 1) is divided into two sub expressions:

• $1 <- l_orderkey + 1
• $2 <- sum($1)

$1 is a simple arithmetic operation, and $2 is an aggregation function. $1 is evaluated in ScanNode because it's just a simple arithmetic operation. So, the evaluation state of l_orderkey + 1 initially is false, but the state will be true after ScanNode. In contrast, sum($1) is evaluated at GroupbyNode. So, its evaluation state is changed after GroupByNode.

Why is TargetListManager necessary?

Expressions used in a query block can be divided into various categories according to the possible Projectable nodes. Their references become available depending on the Projectable node at which expressions are evaluated. It manages the expressions and references for optimized places of expressions. It performs duplicated removal and enables common expressions to be shared with two or more Projectable nodes. It also helps Projectable nodes to find correct column references.

Constructor Summary

Constructors

Constructor and Description
ProjectionPushDownRule.TargetListManager(LogicalPlan plan)

Method Summary

Methods

Modifier and Type	Method and Description
String	add(EvalNode evalNode) Adds an expression without any name.
String	add(Target target)
Iterator<Target>	getFilteredTargets(Set<String> required)
Collection<String>	getNames()
String	getRealReferenceName(String name) This method retrieves the name indicating actual expression that an given alias indicate.
Target	getTarget(String name)
boolean	isEvaluated(String name)
boolean	isNativeAlias(String name) If some expression is duplicated, we call an alias indicating the duplicated expression 'native alias'.
void	markAsEvaluated(Target target)
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

ProjectionPushDownRule.TargetListManager

public ProjectionPushDownRule.TargetListManager(LogicalPlan plan)

Method Detail

isNativeAlias

public boolean isNativeAlias(String name)

If some expression is duplicated, we call an alias indicating the duplicated expression 'native alias'. This method checks whether a reference is native alias or not.

Parameters:

name - The reference name

Returns:

True if the reference is native alias. Otherwise, it will return False.

getRealReferenceName

public String getRealReferenceName(String name)

This method retrieves the name indicating actual expression that an given alias indicate.

Parameters:

name - an alias name

Returns:

Real reference name

add

public String add(EvalNode evalNode)
           throws PlanningException

Adds an expression without any name. It returns an automatically generated name. It can be also used for referring this expression.

Throws:

PlanningException

getNames

public Collection<String> getNames()

add

public String add(Target target)
           throws PlanningException

Throws:

PlanningException

getTarget

public Target getTarget(String name)

isEvaluated

public boolean isEvaluated(String name)

markAsEvaluated

public void markAsEvaluated(Target target)

getFilteredTargets

public Iterator<Target> getFilteredTargets(Set<String> required)

toString

public String toString()

Overrides:

toString in class Object