org.apache.hadoop.hive.ql.optimizer

Class IdentityProjectRemover

java.lang.Object

org.apache.hadoop.hive.ql.optimizer.IdentityProjectRemover

All Implemented Interfaces:

Transform

public class IdentityProjectRemover
extends Object
implements Transform

This optimization tries to remove SelectOperator from tree which don't do any processing except forwarding columns from its parent to its children. e.g., select * from (select * from src where key = value) t1 join (select * from src where key = value) t2; Query tree Without this optimization: TS -> FIL -> SEL -> RS -> JOIN -> SEL -> FS TS -> FIL -> SEL -> RS -> With this optimization TS -> FIL -> RS -> JOIN -> FS TS -> FIL -> RS -> Note absence of select operator after filter and after join operator. Also, see : identity_proj_remove.q

Constructor Summary

Constructors

Constructor and Description
IdentityProjectRemover()

Method Summary

Methods

Modifier and Type	Method and Description
ParseContext	transform(ParseContext pctx) All transformation steps implement this interface.

Methods inherited from class java.lang.Object

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

Constructor Detail

IdentityProjectRemover

public IdentityProjectRemover()

Method Detail

transform

public ParseContext transform(ParseContext pctx)
                       throws SemanticException

Description copied from interface: Transform

All transformation steps implement this interface.

Specified by:

transform in interface Transform

Parameters:

pctx - input parse context

Returns:

ParseContext

Throws:

SemanticException