HDFS-17237. Remove IPCLoggerChannelMetrics when the logger is closed

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannel.java

@@ -206,6 +206,7 @@ public void close() {
       // making any more calls after this point (eg clear the queue)
       RPC.stopProxy(proxy);
     }
+    metrics.unregister();
   }
 
   protected QJournalProtocol getProxy() throws IOException {

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannelMetrics.java

@@ -18,7 +18,6 @@
 package org.apache.hadoop.hdfs.qjournal.client;
 
 import java.net.InetSocketAddress;
-import java.util.Map;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
@@ -29,8 +28,6 @@
 import org.apache.hadoop.metrics2.lib.MetricsRegistry;
 import org.apache.hadoop.metrics2.lib.MutableQuantiles;
 
-import org.apache.hadoop.thirdparty.com.google.common.collect.Maps;
-
 /**
  * The metrics for a journal from the writer's perspective.
  */
@@ -43,21 +40,6 @@ class IPCLoggerChannelMetrics {
   private final MutableQuantiles[] writeEndToEndLatencyQuantiles;
   private final MutableQuantiles[] writeRpcLatencyQuantiles;
 
-
-  /**
-   * In the case of the NN transitioning between states, edit logs are closed
-   * and reopened. Thus, the IPCLoggerChannel instance that writes to a
-   * given JournalNode may change over the lifetime of the process.
-   * However, metrics2 doesn't have a function to unregister a set of metrics
-   * and fails if a new metrics class is registered with the same name
-   * as the existing one. Hence, we have to maintain our own registry
-   * ("multiton") here, so that we have exactly one metrics instance
-   * per JournalNode, and switch out the pointer to the underlying
-   * IPCLoggerChannel instance.
-   */
-  private static final Map<String, IPCLoggerChannelMetrics> REGISTRY =
-      Maps.newHashMap();
-
   private IPCLoggerChannelMetrics(IPCLoggerChannel ch) {
     this.ch = ch;
 
@@ -81,25 +63,16 @@ private IPCLoggerChannelMetrics(IPCLoggerChannel ch) {
       writeRpcLatencyQuantiles = null;
     }
   }
-
-  private void setChannel(IPCLoggerChannel ch) {
-    assert ch.getRemoteAddress().equals(this.ch.getRemoteAddress());
-    this.ch = ch;
+
+  public void unregister() {
+    DefaultMetricsSystem.instance().unregisterSource(getName(ch));
   }
 
   static IPCLoggerChannelMetrics create(IPCLoggerChannel ch) {
     String name = getName(ch);
-    synchronized (REGISTRY) {
-      IPCLoggerChannelMetrics m = REGISTRY.get(name);
-      if (m != null) {
-        m.setChannel(ch);
-      } else {
-        m = new IPCLoggerChannelMetrics(ch);
-        DefaultMetricsSystem.instance().register(name, null, m);
-        REGISTRY.put(name, m);
-      }
-      return m;
-    }
+    IPCLoggerChannelMetrics m = new IPCLoggerChannelMetrics(ch);
+    DefaultMetricsSystem.instance().register(name, null, m);
+    return m;
   }
 
   private static String getName(IPCLoggerChannel ch) {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/client/TestIPCLoggerChannel.java

@@ -24,12 +24,13 @@
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.TimeUnit;
 
+import org.apache.hadoop.metrics2.MetricsSource;
+import org.apache.hadoop.metrics2.MetricsSystem;
+import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hdfs.DFSConfigKeys;
-import org.apache.hadoop.hdfs.qjournal.client.IPCLoggerChannel;
-import org.apache.hadoop.hdfs.qjournal.client.LoggerTooFarBehindException;
 import org.apache.hadoop.hdfs.qjournal.protocol.QJournalProtocol;
 import org.apache.hadoop.hdfs.qjournal.protocol.RequestInfo;
 import org.apache.hadoop.hdfs.server.namenode.NameNodeLayoutVersion;
@@ -178,4 +179,20 @@ public void testStopSendingEditsWhenOutOfSync() throws Exception {
 
     ch.sendEdits(3L, 3L, 1, FAKE_DATA).get();
   }
+
+  @Test
+  public void testMetricsRemovedOnClose() {
+    MetricsSystem metricsSystem = DefaultMetricsSystem.instance();
+    String sourceName = "IPCLoggerChannel-"
+        + FAKE_ADDR.getAddress().getHostAddress()
+        + "-" + FAKE_ADDR.getPort();
+    // Ensure the metrics exist
+    MetricsSource source = metricsSystem.getSource(sourceName);
+    assertNotNull(source);
+
+    ch.close();
+    // ensure the metrics are removed.
+    source = metricsSystem.getSource(sourceName);
+    assertNull(source);
+  }
 }