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

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

All Implemented Interfaces:

Transform

public class StatsOptimizer
extends Object
implements Transform

There is a set of queries which can be answered entirely from statistics stored in metastore. Examples of such queries are count(*), count(a), max(a), min(b) etc. Hive already collects these basic statistics for query planning purposes. These same statistics can be used to answer queries also. Optimizer looks at query plan to determine if it can answer query using statistics and than change the plan to answer query entirely using statistics stored in metastore.

Constructor Summary

StatsOptimizer()

Method Summary

ParseContext

transform(ParseContext pctx) All transformation steps implement this interface.

Methods inherited from class java.lang.Object

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

Constructor Detail

StatsOptimizer

public StatsOptimizer()

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