HDFS-15757 RBF: Improving Router Connection Management

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/metrics/FederationRPCMBean.java

@@ -76,6 +76,21 @@ public interface FederationRPCMBean {
    */
   int getRpcClientNumActiveConnections();
 
+  /**
+   * Get the number of idle RPC connections between the Router and the NNs.
+   * @return Number of idle RPC connections between the Router and the NNs.
+   */
+  int getRpcClientNumIdleConnections();
+
+  /**
+   * Get the number of recently active RPC connections between
+   * the Router and the NNs.
+   *
+   * @return Number of recently active RPC connections between
+   * the Router and the NNs.
+   */
+  int getRpcClientNumActiveConnectionsRecently();
+
   /**
    * Get the number of RPC connections to be created.
    * @return Number of RPC connections to be created.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/metrics/FederationRPCMetrics.java

@@ -208,6 +208,16 @@ public int getRpcClientNumActiveConnections() {
     return rpcServer.getRPCClient().getNumActiveConnections();
   }
 
+  @Override
+  public int getRpcClientNumIdleConnections() {
+    return rpcServer.getRPCClient().getNumIdleConnections();
+  }
+
+  @Override
+  public int getRpcClientNumActiveConnectionsRecently() {
+    return rpcServer.getRPCClient().getNumActiveConnectionsRecently();
+  }
+
   @Override
   public int getRpcClientNumCreatingConnections() {
     return rpcServer.getRPCClient().getNumCreatingConnections();

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/ConnectionContext.java

@@ -18,9 +18,13 @@
 package org.apache.hadoop.hdfs.server.federation.router;
 
 import java.net.InetSocketAddress;
+import java.util.concurrent.TimeUnit;
 
 import org.apache.hadoop.hdfs.NameNodeProxiesClient.ProxyAndInfo;
 import org.apache.hadoop.ipc.RPC;
+import org.apache.hadoop.util.Time;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Context to track a connection in a {@link ConnectionPool}. When a client uses
@@ -36,13 +40,19 @@
  */
 public class ConnectionContext {
 
+  private static final Logger LOG =
+      LoggerFactory.getLogger(ConnectionContext.class);
+
   /** Client for the connection. */
   private final ProxyAndInfo<?> client;
   /** How many threads are using this connection. */
   private int numThreads = 0;
   /** If the connection is closed. */
   private boolean closed = false;
-
+  /** Last timestamp the connection was active. */
+  private long lastActiveTs = 0;
+  /** The connection's active status would expire after this window. */
+  private final static long ACTIVE_WINDOW_TIME = TimeUnit.SECONDS.toMillis(30);
 
   public ConnectionContext(ProxyAndInfo<?> connection) {
     this.client = connection;
@@ -57,6 +67,16 @@ public synchronized boolean isActive() {
     return this.numThreads > 0;
   }
 
+  /**
+   * Check if the connection is/was active recently.
+   *
+   * @return True if the connection is active or
+   * was active in the past period of time.
+   */
+  public synchronized boolean isActiveRecently() {
+    return Time.monotonicNow() - this.lastActiveTs <= ACTIVE_WINDOW_TIME;
+  }
+
   /**
    * Check if the connection is closed.
    *
@@ -83,30 +103,41 @@ public synchronized boolean isUsable() {
    */
   public synchronized ProxyAndInfo<?> getClient() {
     this.numThreads++;
+    this.lastActiveTs = Time.monotonicNow();
     return this.client;
   }
 
   /**
-   * Release this connection. If the connection was closed, close the proxy.
-   * Otherwise, mark the connection as not used by us anymore.
+   * Release this connection.
    */
   public synchronized void release() {
-    if (--this.numThreads == 0 && this.closed) {
-      close();
+    if (this.numThreads > 0) {
+      this.numThreads--;
     }
   }
 
   /**
-   * We will not use this connection anymore. If it's not being used, we close
-   * it. Otherwise, we let release() do it once we are done with it.
+   * Close a connection. Only idle connections can be closed since
+   * the RPC proxy would be shut down immediately.
+   *
+   * @param force whether the connection should be closed anyway.
    */
-  public synchronized void close() {
-    this.closed = true;
-    if (this.numThreads == 0) {
-      Object proxy = this.client.getProxy();
-      // Nobody should be using this anymore so it should close right away
-      RPC.stopProxy(proxy);
+  public synchronized void close(boolean force) {
+    if (!force && this.numThreads > 0) {
+      // this is an erroneous case but we have to close the connection
+      // anyway since there will be connection leak if we don't do so
+      // the connection has been moved out of the pool
+      LOG.error("Active connection with {} handlers will be closed",
+          this.numThreads);
     }
+    this.closed = true;
+    Object proxy = this.client.getProxy();
+    // Nobody should be using this anymore so it should close right away
+    RPC.stopProxy(proxy);
+  }
+
+  public synchronized void close() {
+    close(false);
   }
 
   @Override

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/ConnectionManager.java

@@ -281,6 +281,42 @@ public int getNumActiveConnections() {
     return total;
   }
 
+  /**
+   * Get number of idle connections.
+   *
+   * @return Number of active connections.
+   */
+  public int getNumIdleConnections() {
+    int total = 0;
+    readLock.lock();
+    try {
+      for (ConnectionPool pool : this.pools.values()) {
+        total += pool.getNumIdleConnections();
+      }
+    } finally {
+      readLock.unlock();
+    }
+    return total;
+  }
+
+  /**
+   * Get number of recently active connections.
+   *
+   * @return Number of recently active connections.
+   */
+  public int getNumActiveConnectionsRecently() {
+    int total = 0;
+    readLock.lock();
+    try {
+      for (ConnectionPool pool : this.pools.values()) {
+        total += pool.getNumActiveConnectionsRecently();
+      }
+    } finally {
+      readLock.unlock();
+    }
+    return total;
+  }
+
   /**
    * Get the number of connections to be created.
    *
@@ -327,12 +363,21 @@ void cleanup(ConnectionPool pool) {
       // Check if the pool hasn't been active in a while or not 50% are used
       long timeSinceLastActive = Time.now() - pool.getLastActiveTime();
       int total = pool.getNumConnections();
-      int active = pool.getNumActiveConnections();
+      // Active is a transient status in many cases for a connection since
+      // the handler thread uses the connection very quickly. Thus the number
+      // of connections with handlers using at the call time is constantly low.
+      // Recently active is more lasting status and it shows how many
+      // connections have been used with a recent time period. (i.e. 30 seconds)
+      int active = pool.getNumActiveConnectionsRecently();
       float poolMinActiveRatio = pool.getMinActiveRatio();
       if (timeSinceLastActive > connectionCleanupPeriodMs ||
           active < poolMinActiveRatio * total) {
-        // Remove and close 1 connection
-        List<ConnectionContext> conns = pool.removeConnections(1);
+        // Be greedy here to close as many connections as possible in one shot
+        // The number should at least be 1
+        int targetConnectionsCount = Math.max(1,
+            (int)(poolMinActiveRatio * total) - active);
+        List<ConnectionContext> conns =
+            pool.removeConnections(targetConnectionsCount);
         for (ConnectionContext conn : conns) {
           conn.close();
         }
@@ -414,7 +459,7 @@ public void run() {
           ConnectionPool pool = this.queue.take();
           try {
             int total = pool.getNumConnections();
-            int active = pool.getNumActiveConnections();
+            int active = pool.getNumActiveConnectionsRecently();
             float poolMinActiveRatio = pool.getMinActiveRatio();
             if (pool.getNumConnections() < pool.getMaxSize() &&
                 active >= poolMinActiveRatio * total) {

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/ConnectionPool.java

@@ -252,19 +252,23 @@ public synchronized void addConnection(ConnectionContext conn) {
    */
   public synchronized List<ConnectionContext> removeConnections(int num) {
     List<ConnectionContext> removed = new LinkedList<>();
-
-    // Remove and close the last connection
-    List<ConnectionContext> tmpConnections = new ArrayList<>();
-    for (int i=0; i<this.connections.size(); i++) {
-      ConnectionContext conn = this.connections.get(i);
-      if (i < this.minSize || i < this.connections.size() - num) {
-        tmpConnections.add(conn);
-      } else {
-        removed.add(conn);
+    if (this.connections.size() > this.minSize) {
+      int targetCount = Math.min(num, this.connections.size() - this.minSize);
+      // Remove and close targetCount of connections
+      List<ConnectionContext> tmpConnections = new ArrayList<>();
+      for (int i = 0; i < this.connections.size(); i++) {
+        ConnectionContext conn = this.connections.get(i);
+        // Only pick idle connections to close
+        if (removed.size() < targetCount && conn.isUsable()) {
+          removed.add(conn);
+        } else {
+          tmpConnections.add(conn);
+        }
       }
+      this.connections = tmpConnections;
     }
-    this.connections = tmpConnections;
-
+    LOG.debug("Expected to remove {} connection " +
+        "and actually removed {} connections", num, removed.size());
     return removed;
   }
 
@@ -278,7 +282,7 @@ protected synchronized void close() {
         this.connectionPoolId, timeSinceLastActive);
 
     for (ConnectionContext connection : this.connections) {
-      connection.close();
+      connection.close(true);
     }
     this.connections.clear();
   }
@@ -309,6 +313,39 @@ protected int getNumActiveConnections() {
     return ret;
   }
 
+  /**
+   * Number of usable i.e. no active thread connections.
+   *
+   * @return Number of idle connections
+   */
+  protected int getNumIdleConnections() {
+    int ret = 0;
+
+    List<ConnectionContext> tmpConnections = this.connections;
+    for (ConnectionContext conn : tmpConnections) {
+      if (conn.isUsable()) {
+        ret++;
+      }
+    }
+    return ret;
+  }
+
+  /**
+   * Number of active connections recently in the pool.
+   *
+   * @return Number of active connections recently.
+   */
+  protected int getNumActiveConnectionsRecently() {
+    int ret = 0;
+    List<ConnectionContext> tmpConnections = this.connections;
+    for (ConnectionContext conn : tmpConnections) {
+      if (conn.isActiveRecently()) {
+        ret++;
+      }
+    }
+    return ret;
+  }
+
   /**
    * Get the last time the connection pool was used.
    *
@@ -331,12 +368,18 @@ public String toString() {
   public String getJSON() {
     final Map<String, String> info = new LinkedHashMap<>();
     info.put("active", Integer.toString(getNumActiveConnections()));
+    info.put("recent_active",
+        Integer.toString(getNumActiveConnectionsRecently()));
+    info.put("idle", Integer.toString(getNumIdleConnections()));
     info.put("total", Integer.toString(getNumConnections()));
     if (LOG.isDebugEnabled()) {
       List<ConnectionContext> tmpConnections = this.connections;
       for (int i=0; i<tmpConnections.size(); i++) {
         ConnectionContext connection = tmpConnections.get(i);
         info.put(i + " active", Boolean.toString(connection.isActive()));
+        info.put(i + " recent_active",
+            Integer.toString(getNumActiveConnectionsRecently()));
+        info.put(i + " idle", Boolean.toString(connection.isUsable()));
         info.put(i + " closed", Boolean.toString(connection.isClosed()));
       }
     }

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcClient.java

@@ -260,6 +260,24 @@ public int getNumActiveConnections() {
     return this.connectionManager.getNumActiveConnections();
   }
 
+  /**
+   * Total number of idle sockets between the router and NNs.
+   *
+   * @return Number of namenode clients.
+   */
+  public int getNumIdleConnections() {
+    return this.connectionManager.getNumIdleConnections();
+  }
+
+  /**
+   * Total number of active sockets between the router and NNs.
+   *
+   * @return Number of recently active namenode clients.
+   */
+  public int getNumActiveConnectionsRecently() {
+    return this.connectionManager.getNumActiveConnectionsRecently();
+  }
+
   /**
    * Total number of open connection pools to a NN. Each connection pool.
    * represents one user + one NN.