org.apache.hadoop.hive.ql.optimizer.physical
Class MetadataOnlyOptimizer

java.lang.Object
  org.apache.hadoop.hive.ql.optimizer.physical.MetadataOnlyOptimizer

All Implemented Interfaces:

PhysicalPlanResolver

public class MetadataOnlyOptimizer
extends Object
implements PhysicalPlanResolver

MetadataOnlyOptimizer determines to which TableScanOperators "metadata only" optimization can be applied. Such operator must use only partition columns (it is easy to check, because we are after column pruning and all places where the data from the operator is used must go through GroupByOperator distinct or distinct-like aggregations. Aggregation is distinct-like if adding distinct wouldn't change the result, for example min, max. We cannot apply the optimization without group by, because the results depend on the numbers of rows in partitions, for example count(hr) will count all rows in matching partitions.

Constructor Summary

MetadataOnlyOptimizer()

Method Summary

PhysicalContext

resolve(PhysicalContext pctx) All physical plan resolvers have to implement this entry method.

Methods inherited from class java.lang.Object

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

Constructor Detail

MetadataOnlyOptimizer

public MetadataOnlyOptimizer()

Method Detail

resolve

public PhysicalContext resolve(PhysicalContext pctx)
                        throws SemanticException

Description copied from interface: PhysicalPlanResolver

All physical plan resolvers have to implement this entry method.

Specified by:

resolve in interface PhysicalPlanResolver

Returns:

the physical plan

Throws:

SemanticException