package org.apache.lucene.search;
/**
* 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.
*/
import java.io.Serializable;
import java.io.IOException;
import java.util.Map;
import java.util.WeakHashMap;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.util.OpenBitSetDISI;
/**
* Wraps another filter's result and caches it. The purpose is to allow
* filters to simply filter, and then wrap with this class to add caching.
*/
public class CachingWrapperFilter extends Filter {
Filter filter;
/**
* Expert: Specifies how new deletions against a reopened
* reader should be handled.
*
* <p>The default is IGNORE, which means the cache entry
* will be re-used for a given segment, even when that
* segment has been reopened due to changes in deletions.
* This is a big performance gain, especially with
* near-real-timer readers, since you don't hit a cache
* miss on every reopened reader for prior segments.</p>
*
* <p>However, in some cases this can cause invalid query
* results, allowing deleted documents to be returned.
* This only happens if the main query does not rule out
* deleted documents on its own, such as a toplevel
* ConstantScoreQuery. To fix this, use RECACHE to
* re-create the cached filter (at a higher per-reopen
* cost, but at faster subsequent search performance), or
* use DYNAMIC to dynamically intersect deleted docs (fast
* reopen time but some hit to search performance).</p>
*/
public static enum DeletesMode {IGNORE, RECACHE, DYNAMIC};
protected final FilterCache<DocIdSet> cache;
static abstract class FilterCache<T> implements Serializable {
/**
* A transient Filter cache (package private because of test)
*/
// NOTE: not final so that we can dynamically re-init
// after de-serialize
transient Map<Object,T> cache;
private final DeletesMode deletesMode;
public FilterCache(DeletesMode deletesMode) {
this.deletesMode = deletesMode;
}
public synchronized T get(IndexReader reader, Object coreKey, Object delCoreKey) throws IOException {
T value;
if (cache == null) {
cache = new WeakHashMap<Object,T>();
}
if (deletesMode == DeletesMode.IGNORE) {
// key on core
value = cache.get(coreKey);
} else if (deletesMode == DeletesMode.RECACHE) {
// key on deletes, if any, else core
value = cache.get(delCoreKey);
} else {
assert deletesMode == DeletesMode.DYNAMIC;
// first try for exact match
value = cache.get(delCoreKey);
if (value == null) {
// now for core match, but dynamically AND NOT
// deletions
value = cache.get(coreKey);
if (value != null && reader.hasDeletions()) {
value = mergeDeletes(reader, value);
}
}
}
return value;
}
protected abstract T mergeDeletes(IndexReader reader, T value);
public synchronized void put(Object coreKey, Object delCoreKey, T value) {
if (deletesMode == DeletesMode.IGNORE) {
cache.put(coreKey, value);
} else if (deletesMode == DeletesMode.RECACHE) {
cache.put(delCoreKey, value);
} else {
cache.put(coreKey, value);
cache.put(delCoreKey, value);
}
}
}
/**
* New deletes are ignored by default, which gives higher
* cache hit rate on reopened readers. Most of the time
* this is safe, because the filter will be AND'd with a
* Query that fully enforces deletions. If instead you
* need this filter to always enforce deletions, pass
* either {@link DeletesMode#RECACHE} or {@link
* DeletesMode#DYNAMIC}.
* @param filter Filter to cache results of
*/
public CachingWrapperFilter(Filter filter) {
this(filter, DeletesMode.IGNORE);
}
/**
* Expert: by default, the cached filter will be shared
* across reopened segments that only had changes to their
* deletions.
*
* @param filter Filter to cache results of
* @param deletesMode See {@link DeletesMode}
*/
public CachingWrapperFilter(Filter filter, DeletesMode deletesMode) {
this.filter = filter;
cache = new FilterCache<DocIdSet>(deletesMode) {
@Override
public DocIdSet mergeDeletes(final IndexReader r, final DocIdSet docIdSet) {
return new FilteredDocIdSet(docIdSet) {
@Override
protected boolean match(int docID) {
return !r.isDeleted(docID);
}
};
}
};
}
/** Provide the DocIdSet to be cached, using the DocIdSet provided
* by the wrapped Filter.
* <p>This implementation returns the given {@link DocIdSet}, if {@link DocIdSet#isCacheable}
* returns <code>true</code>, else it copies the {@link DocIdSetIterator} into
* an {@link OpenBitSetDISI}.
*/
protected DocIdSet docIdSetToCache(DocIdSet docIdSet, IndexReader reader) throws IOException {
if (docIdSet == null) {
// this is better than returning null, as the nonnull result can be cached
return DocIdSet.EMPTY_DOCIDSET;
} else if (docIdSet.isCacheable()) {
return docIdSet;
} else {
final DocIdSetIterator it = docIdSet.iterator();
// null is allowed to be returned by iterator(),
// in this case we wrap with the empty set,
// which is cacheable.
return (it == null) ? DocIdSet.EMPTY_DOCIDSET : new OpenBitSetDISI(it, reader.maxDoc());
}
}
// for testing
int hitCount, missCount;
@Override
public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
final Object coreKey = reader.getFieldCacheKey();
final Object delCoreKey = reader.hasDeletions() ? reader.getDeletesCacheKey() : coreKey;
DocIdSet docIdSet = cache.get(reader, coreKey, delCoreKey);
if (docIdSet != null) {
hitCount++;
return docIdSet;
}
missCount++;
// cache miss
docIdSet = docIdSetToCache(filter.getDocIdSet(reader), reader);
if (docIdSet != null) {
cache.put(coreKey, delCoreKey, docIdSet);
}
return docIdSet;
}
@Override
public String toString() {
return "CachingWrapperFilter("+filter+")";
}
@Override
public boolean equals(Object o) {
if (!(o instanceof CachingWrapperFilter)) return false;
return this.filter.equals(((CachingWrapperFilter)o).filter);
}
@Override
public int hashCode() {
return filter.hashCode() ^ 0x1117BF25;
}
}