smengcl commented on code in PR #4567: URL: https://github.com/apache/ozone/pull/4567#discussion_r1231747963
########## hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/snapshot/SnapshotCache.java: ########## @@ -0,0 +1,323 @@ +/* + * 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.hadoop.ozone.om.snapshot; + +import com.google.common.annotations.VisibleForTesting; +import com.google.common.base.Preconditions; +import com.google.common.cache.CacheLoader; +import org.apache.hadoop.ozone.om.IOmMetadataReader; +import org.apache.hadoop.ozone.om.OmSnapshot; +import org.apache.hadoop.ozone.om.OmSnapshotManager; +import org.apache.hadoop.ozone.om.exceptions.OMException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.io.IOException; +import java.util.Iterator; +import java.util.LinkedHashSet; +import java.util.Map; +import java.util.concurrent.ConcurrentHashMap; + +import static org.apache.hadoop.ozone.om.exceptions.OMException.ResultCodes.FILE_NOT_FOUND; +import static org.apache.hadoop.ozone.om.helpers.SnapshotInfo.SnapshotStatus.SNAPSHOT_ACTIVE; + +/** + * Thread-safe custom unbounded LRU cache to manage open snapshot DB instances. + */ +public class SnapshotCache { + + static final Logger LOG = LoggerFactory.getLogger(SnapshotCache.class); + + // Snapshot cache internal hash map. + // Key: DB snapshot table key + // Value: OmSnapshot instance, each holds a DB instance handle inside + // TODO: Also wrap SoftReference<> around the value? + private final ConcurrentHashMap<String, ReferenceCounted<IOmMetadataReader>> + dbMap; + + // Linked hash set that holds OmSnapshot instances whose reference count + // has reached zero. Those entries are eligible to be evicted and closed. + // Sorted in last used order. + // Least-recently-used entry located at the beginning. + // TODO: Check thread safety. Try ConcurrentHashMultiset ? Review Comment: nice. thanks! -- 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] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
