org.apache.hadoop.hive.ql.optimizer
Class JoinReorder

java.lang.Object
  org.apache.hadoop.hive.ql.optimizer.JoinReorder

All Implemented Interfaces:

Transform

public class JoinReorder
extends Object
implements Transform

Implementation of rule-based join table reordering optimization. User passes hints to specify which tables are to be streamed and they are moved to have largest tag so that they are processed last. In future, once statistics are implemented, this transformation can also be done based on costs.

Constructor Summary

JoinReorder()

Method Summary

ParseContext

transform(ParseContext pactx) Transform the query tree.

Methods inherited from class java.lang.Object

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

Constructor Detail

JoinReorder

public JoinReorder()

Method Detail

transform

public ParseContext transform(ParseContext pactx)
                       throws SemanticException

Transform the query tree. For each join, check which reduce sink will output the biggest result (based on STREAMTABLE hints) and give it the biggest tag so that it gets streamed.

Specified by:

transform in interface Transform

Parameters:

pactx - current parse context

Returns:

ParseContext

Throws:

SemanticException