jpountz commented on a change in pull request #916: LUCENE-8213: Asynchronous
Caching in LRUQueryCache
URL: https://github.com/apache/lucene-solr/pull/916#discussion_r331190828
##########
File path: lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java
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@@ -88,13 +92,47 @@
* @lucene.experimental
*/
public class LRUQueryCache implements QueryCache, Accountable {
+ /** Act as key for the inflight queries map */
+ private static class MapKey {
+ private final Query query;
+ private final IndexReader.CacheKey cacheKey;
+
+ public MapKey(Query query, IndexReader.CacheKey cacheKey) {
+ this.query = query;
+ this.cacheKey = cacheKey;
+ }
+
+ public Query getQuery() {
+ return query;
+ }
+
+ public IndexReader.CacheKey getCacheKey() {
+ return cacheKey;
+ }
+
+ @Override
+ public int hashCode() { return query.hashCode() ^ cacheKey.hashCode(); }
Review comment:
Can you use the usual polynomial formula `h0 + 31 * (h1 + 31 * ( ... ))`.
The use of `^` is fine here, but it is a source of performance bugs in some
scenarios. For instance Java's AbstractMap.Entry does this, which means that
whenever you map a key to itself, the hashcode is 0 (because both hashcodes are
equal). This is a lot of collisions if you have lots of entries that have the
same key and value. So I prefer avoiding this pattern.
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