org.apache.hadoop.hive.ql.optimizer

Class SemiJoinReductionMerge

java.lang.Object

org.apache.hadoop.hive.ql.optimizer.Transform

org.apache.hadoop.hive.ql.optimizer.SemiJoinReductionMerge

public class SemiJoinReductionMerge
extends Transform

A transformation that merges multiple single-column semi join reducers to one multi-column semi join reducer.

Semi join reducers are comprised from two parts:

• Filter creation from the source relation and broadcast: SOURCE - SEL - GB1 - RS1 - GB2 - RS2
• Filter application on the target relation: TS - FIL[in_bloom(col)]

An example of the transformation on three single column semi join reducers is shown below. The plan is simplified for presentation purposes.

BEFORE:

        / SEL[fname] - GB1 - RS1 - GB2 - RS2  \
 SOURCE - SEL[lname] - GB1 - RS1 - GB2 - RS2  -> TS[Author] - FIL[in_bloom(fname) ^ in_bloom(lname) ^ in_bloom(age)]
        \ SEL[age]   - GB1 - RS1 - GB2 - RS2  /
 

AFTER:

 SOURCE - SEL[fname, lname, age] - GB1 - RS1 - GB2 - RS2 -> TS[Author] - FIL[in_bloom(hash(fname,lname,age)]
 

Constructor Summary

Constructors

Constructor and Description
SemiJoinReductionMerge()

Method Summary

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

Methods inherited from class org.apache.hadoop.hive.ql.optimizer.Transform

beginPerfLogging, endPerfLogging, endPerfLogging

Methods inherited from class java.lang.Object

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

Constructor Detail

SemiJoinReductionMerge

public SemiJoinReductionMerge()

Method Detail

transform

public ParseContext transform(ParseContext parseContext)
                       throws SemanticException

Description copied from class: Transform

All transformation steps implement this interface.

Specified by:

transform in class Transform

Parameters:

parseContext - input parse context

Returns:

ParseContext

Throws:

SemanticException