org.eigenbase.rel.metadata
Class CachingRelMetadataProvider

java.lang.Object
  org.eigenbase.rel.metadata.CachingRelMetadataProvider

All Implemented Interfaces:

RelMetadataProvider

public class CachingRelMetadataProvider
extends Object
implements RelMetadataProvider

CachingRelMetadataProvider implements the RelMetadataProvider interface by caching results from an underlying provider.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/rel/metadata/CachingRelMetadataProvider.java#7 $

Author:

John V. Sichi

Nested Class Summary

private static class

CachingRelMetadataProvider.CacheEntry

Field Summary

private Map<List,CachingRelMetadataProvider.CacheEntry>	cache
private RelOptPlanner	planner
private RelMetadataProvider	underlyingProvider

Constructor Summary

CachingRelMetadataProvider(RelMetadataProvider underlyingProvider, RelOptPlanner planner)

Method Summary

Object

getRelMetadata(RelNode rel, String metadataQueryName, Object[] args) Retrieves metadata about a relational expression.

Methods inherited from class java.lang.Object

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

Field Detail

cache

private final Map<List,CachingRelMetadataProvider.CacheEntry> cache

underlyingProvider

private final RelMetadataProvider underlyingProvider

planner

private final RelOptPlanner planner

Constructor Detail

CachingRelMetadataProvider

public CachingRelMetadataProvider(RelMetadataProvider underlyingProvider,
                                  RelOptPlanner planner)

Method Detail

getRelMetadata

public Object getRelMetadata(RelNode rel,
                             String metadataQueryName,
                             Object[] args)

Description copied from interface: RelMetadataProvider

Retrieves metadata about a relational expression.

Specified by:

getRelMetadata in interface RelMetadataProvider

Parameters:

rel - relational expression of interest

metadataQueryName - name of metadata query to invoke

args - arguments to metadata query (expected number and type depend on query name; must have well-defined hashCode/equals for use by caching); null can be used instead of empty array

Returns:

metadata result (actual type depends on query name), or null if the provider cannot answer the given query/rel combination; it is better to return null than to return a possibly incorrect answer