iprithv commented on code in PR #16212:
URL: https://github.com/apache/lucene/pull/16212#discussion_r3378503969


##########
lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java:
##########
@@ -1059,6 +1059,35 @@ void remove(QueryCacheKey queryCacheKey) {
       remove(queryCacheKey, -1);
     }
 
+    /**
+     * Remove all cache entries whose segment cache key is in {@code 
keysToRemove} or whose query is
+     * in {@code queriesToRemove}. Runs under the partition write lock so that 
iteration of the
+     * underlying {@code HashMap} does not race with concurrent mutation.
+     *
+     * <p>Note: {@link #remove(QueryCacheKey, long)} re-acquires the write 
lock, which is safe
+     * because {@link 
java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock} is reentrant.
+     * This matches the pattern used by {@link #evictIfNecessary()}.
+     */
+    void removeMatching(Set<IndexReader.CacheKey> keysToRemove, Set<Query> 
queriesToRemove) {
+      writeLock.lock();

Review Comment:
   cleanUp() runs at most once per minute (or manually). lock is per-partition, 
not global.. with 16 partitions we only block 1/16th of the cache at a time. 
this is also the same pattern evictIfNecessary() already uses, it holds the 
write lock while iterating and removing entries. old code iterated 
HashMap.keySet() with no lock at all, which is what caused the 
ConcurrentModificationException.



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