org.apache.hadoop.hive.ql.optimizer.index

Class RewriteGBUsingIndex

java.lang.Object

org.apache.hadoop.hive.ql.optimizer.index.RewriteGBUsingIndex

All Implemented Interfaces:

Transform

public class RewriteGBUsingIndex
extends Object
implements Transform

RewriteGBUsingIndex is implemented as one of the Rule-based Optimizations. Implements optimizations for GroupBy clause rewrite using aggregate index. This optimization rewrites GroupBy query over base table to the query over simple table-scan over index table, if there is index on the group by key(s) or the distinct column(s). E.g. select count(key) from table group by key; to select sum(_count_of_key) from idx_table group by key; The rewrite supports following queries:

• Queries having only those col refs that are in the index key.
• Queries that have index key col refs
  • in SELECT
  • in WHERE
  • in GROUP BY
• Queries with agg func COUNT(index key col ref) in SELECT
• Queries with SELECT DISTINCT index_key_col_refs
• Queries having a subquery satisfying above condition (only the subquery is rewritten)

See Also:

AggregateIndexHandler, IndexUtils, RewriteCanApplyCtx, RewriteCanApplyProcFactory, RewriteParseContextGenerator, RewriteQueryUsingAggregateIndexCtx, For test cases, @see ql_rewrite_gbtoidx.q

Constructor Summary

Constructors

Constructor and Description
RewriteGBUsingIndex()

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

RewriteGBUsingIndex

public RewriteGBUsingIndex()

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