sgup432 commented on code in PR #16212:
URL: https://github.com/apache/lucene/pull/16212#discussion_r3377119891
##########
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:
We shouldn't do this. As by doing this, we are essentially taking a global
lock per partition, and then iterating over all the partition cache keys, and
most of the time you may end up clearing nothing or only few. Instead we should
only take write lock when required ie when we need to remove a certain key.
As mentioned below, lets return a point in time snapshot key set, and work
with that?
##########
lucene/core/src/java/org/apache/lucene/search/LRUQueryCache.java:
##########
@@ -1290,14 +1319,8 @@ public synchronized void cleanUp() {
keysToClean.removeAll(keysToCleanCopy);
queriesToClean.removeAll(queriesToCleanCopy);
- for (QueryCacheKey queryCacheKey : keys()) {
Review Comment:
Why not just return a snapshot/copy of cache keys here instead? That way we
won't run into Concurrent modification exception. Also the approach taken as
part of this PR will regress the performance due to conservative locking.
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