lhotari commented on code in PR #24833: URL: https://github.com/apache/pulsar/pull/24833#discussion_r2466095497
########## pulsar-broker-common/src/main/java/org/apache/pulsar/broker/topiclistlimit/TopicListSizeResultCache.java: ########## @@ -0,0 +1,137 @@ +/* + * 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. + */ +package org.apache.pulsar.broker.topiclistlimit; + +import com.github.benmanes.caffeine.cache.Cache; +import com.github.benmanes.caffeine.cache.Caffeine; +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.atomic.AtomicLong; +import java.util.concurrent.atomic.AtomicReference; +import org.apache.pulsar.common.api.proto.CommandGetTopicsOfNamespace; + +/** + * A cache for storing and managing topic list size estimates in namespaces. + * This class provides functionality to: + * - Cache and retrieve topic list size estimates for different namespaces and modes + * - Handle concurrent requests for topic list sizes efficiently + * - Maintain and update size estimates based on actual topic list sizes + * - Prevent thundering herd problems when multiple concurrent requests for a namespace are made without + * a previous size estimate + * The cache uses namespace name and topic list mode (PERSISTENT/NON_PERSISTENT/ALL) as keys + * and maintains size estimates that are refined with actual usage. + */ +public class TopicListSizeResultCache { + // 10kB initial estimate for topic list heap size + private static final long INITIAL_TOPIC_LIST_HEAP_SIZE = 10 * 1024; + + private Cache<CacheKey, ResultHolder> topicListSizeCache = Caffeine.newBuilder() + .maximumSize(10000) + .build(); + + record CacheKey(String namespaceName, CommandGetTopicsOfNamespace.Mode mode) { + } + + /** + * Holds the topic list size estimate and future for the topic list size. + * The size is returned by calling {@link #getSizeAsync()} method which is asynchronous. + * The estimate is updated by calling {@link #updateSize(long)} method. + */ + public static class ResultHolder { + private final AtomicReference<CompletableFuture<Long>> topicListSizeFuture = Review Comment: This is necessary for the behavior that the first request passes through to resolve the size. This behavior is explained in the javadoc of the getSizeAsync method. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
