/*
* Created on 25-Jan-2006
*/
package org.apache.lucene.xmlparser.builders;
import java.util.Map.Entry;
import org.apache.lucene.search.CachingWrapperFilter;
import org.apache.lucene.search.Filter;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryFilter;
import org.apache.lucene.xmlparser.DOMUtils;
import org.apache.lucene.xmlparser.FilterBuilder;
import org.apache.lucene.xmlparser.FilterBuilderFactory;
import org.apache.lucene.xmlparser.ParserException;
import org.apache.lucene.xmlparser.QueryBuilder;
import org.apache.lucene.xmlparser.QueryBuilderFactory;
import org.w3c.dom.Element;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Filters are cached in an LRU Cache keyed on the contained query or filter object. Using this will
* speed up overall performance for repeated uses of the same expensive query/filter. The sorts of
* queries/filters likely to benefit from caching need not necessarily be complex - e.g. simple
* TermQuerys with a large DF (document frequency) can be expensive on large indexes.
* A good example of this might be a term query on a field with only 2 possible values -
* "true" or "false". In a large index, querying or filtering on this field requires reading
* millions of document ids from disk which can more usefully be cached as a filter bitset.
*
* For Queries/Filters to be cached and reused the object must implement hashcode and
* equals methods correctly so that duplicate queries/filters can be detected in the cache.
*
* The CoreParser.maxNumCachedFilters property can be used to control the size of the LRU
* Cache established during the construction of CoreParser instances.
*
* @author maharwood
*/
public class CachedFilterBuilder implements FilterBuilder {
private QueryBuilderFactory queryFactory;
private FilterBuilderFactory filterFactory;
private LRUCache filterCache = null;
private int cacheSize;
public CachedFilterBuilder(QueryBuilderFactory queryFactory,
FilterBuilderFactory filterFactory,int cacheSize)
{
this.queryFactory=queryFactory;
this.filterFactory=filterFactory;
this.cacheSize=cacheSize;
}
public Filter getFilter(Element e) throws ParserException
{
Element childElement = DOMUtils.getFirstChildOrFail(e);
if (filterCache == null)
{
filterCache = new LRUCache(cacheSize);
}
// Test to see if child Element is a query or filter that needs to be
// cached
QueryBuilder qb = queryFactory.getQueryBuilder(childElement
.getNodeName());
Object cacheKey = null;
Query q = null;
Filter f = null;
if (qb != null)
{
q = qb.getQuery(childElement);
cacheKey = q;
} else
{
f = filterFactory.getFilter(childElement);
cacheKey = f;
}
Filter cachedFilter = null;
synchronized (filterCache)
{ // check cache
cachedFilter = (Filter) filterCache.get(cacheKey);
if (cachedFilter != null)
{
return cachedFilter; // cache hit
}
}
//cache miss
if (qb != null)
{
cachedFilter = new QueryFilter(q);
} else
{
cachedFilter = new CachingWrapperFilter(f);
}
synchronized (filterCache)
{ // update cache
filterCache.put(cacheKey, cachedFilter);
}
return cachedFilter;
}
static class LRUCache extends java.util.LinkedHashMap
{
public LRUCache(int maxsize)
{
super(maxsize * 4 / 3 + 1, 0.75f, true);
this.maxsize = maxsize;
}
protected int maxsize;
protected boolean removeEldestEntry(Entry eldest)
{
return size() > maxsize;
}
}
}