/*
* Created on 25-Jan-2006
*/
package org.apache.lucene.queryparser.xml.builders;
import org.apache.lucene.queryparser.xml.*;
import org.apache.lucene.search.CachingWrapperFilter;
import org.apache.lucene.search.Filter;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryWrapperFilter;
import org.w3c.dom.Element;
import java.util.Map;
/*
* 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.
* <p/>
* 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.
* <p/>
* The CoreParser.maxNumCachedFilters property can be used to control the size of the LRU
* Cache established during the construction of CoreParser instances.
*/
public class CachedFilterBuilder implements FilterBuilder {
private final QueryBuilderFactory queryFactory;
private final FilterBuilderFactory filterFactory;
private LRUCache<Object, Filter> filterCache;
private final int cacheSize;
public CachedFilterBuilder(QueryBuilderFactory queryFactory,
FilterBuilderFactory filterFactory,
int cacheSize) {
this.queryFactory = queryFactory;
this.filterFactory = filterFactory;
this.cacheSize = cacheSize;
}
@Override
public synchronized Filter getFilter(Element e) throws ParserException {
Element childElement = DOMUtils.getFirstChildOrFail(e);
if (filterCache == null) {
filterCache = new LRUCache<Object, Filter>(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 = filterCache.get(cacheKey);
if (cachedFilter != null) {
return cachedFilter; // cache hit
}
//cache miss
if (qb != null) {
cachedFilter = new QueryWrapperFilter(q);
} else {
cachedFilter = new CachingWrapperFilter(f);
}
filterCache.put(cacheKey, cachedFilter);
return cachedFilter;
}
static class LRUCache<K, V> extends java.util.LinkedHashMap<K, V> {
public LRUCache(int maxsize) {
super(maxsize * 4 / 3 + 1, 0.75f, true);
this.maxsize = maxsize;
}
protected int maxsize;
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
return size() > maxsize;
}
}
}