lhotari commented on code in PR #24833: URL: https://github.com/apache/pulsar/pull/24833#discussion_r2466350154
########## 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 = + new AtomicReference<>(null); + private final AtomicLong existingSizeRef = new AtomicLong(-1L); + + /** + * Get the topic list size estimate. The first request will return the initial estimate + * and update the estimate based on the returned size of the topic list. Other concurrent requests + * will wait for the first request to complete and use the estimate of the first request. + * Subsequent requests will use estimate which gets updated based on the returned size of the topic list + * of each request. + * @return a future that will return the topic list size estimate + */ + public CompletableFuture<Long> getSizeAsync() { + if (topicListSizeFuture.compareAndSet(null, new CompletableFuture<>())) { + // let the first request proceed with the initial estimate + return CompletableFuture.completedFuture(INITIAL_TOPIC_LIST_HEAP_SIZE); + } else { + // all other requests wait for the first one to complete + return topicListSizeFuture.get(); + } + } + + /** + * Update the topic list size estimate. The new estimated size will be updated by calculating the average + * of the existing and the new size. If the difference between the new and the existing size is less than 1, + * no update will be done. + * @param actualSize the actual size of the topic list + */ + public void updateSize(long actualSize) { Review Comment: Adding comments -- 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]
