[GitHub] [hbase] sunhelly commented on a change in pull request #3800: HBASE-26347 Support detect and exclude slow DNs in fan-out of WAL

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sunhelly commented on a change in pull request #3800:
URL: https://github.com/apache/hbase/pull/3800#discussion_r762812910



##########
File path: hbase-asyncfs/src/main/java/org/apache/hadoop/hbase/io/asyncfs/monitor/ExcludeDatanodeManager.java
##########
@@ -0,0 +1,120 @@
+/*
+ * 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.hbase.io.asyncfs.monitor;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.TimeUnit;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hbase.conf.ConfigurationObserver;
+import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.apache.hbase.thirdparty.com.google.common.cache.Cache;
+import org.apache.hbase.thirdparty.com.google.common.cache.CacheBuilder;
+
+/**
+ * The class to manage the excluded datanodes of the WALs on the regionserver.
+ */
+@InterfaceAudience.Private
+public class ExcludeDatanodeManager implements ConfigurationObserver {
+  private static final Logger LOG = LoggerFactory.getLogger(ExcludeDatanodeManager.class);
+
+  /**
+   * Configure for the max count the excluded datanodes.
+   */
+  private static final String WAL_MAX_EXCLUDE_SLOW_DATANODE_COUNT_KEY =
+    "hbase.regionserver.async.wal.max.exclude.datanode.count";
+  private static final int DEFAULT_WAL_MAX_EXCLUDE_SLOW_DATANODE_COUNT = 3;
+
+  /**
+   * Configure for the TTL time of the datanodes excluded
+   */
+  private static final String WAL_EXCLUDE_DATANODE_TTL_KEY =
+    "hbase.regionserver.async.wal.exclude.datanode.info.ttl.hour";
+  private static final int DEFAULT_WAL_EXCLUDE_DATANODE_TTL = 6; // 6 hours
+
+  private volatile Cache<DatanodeInfo, Long> excludeDNsCache;

Review comment:
       This cache can be concurrently read and written by WALs of different group, so I make it be volatile to let the change visible to all threads.




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