SERVER-28652 Log the size of connection pools when we make new egress connections

(cherry-picked from commit 0727327d247902253342c988fad307ce07b3fb01)

3 files changed, 27 insertions, 3 deletions

diff --git a/src/mongo/executor/connection_pool.cpp b/src/mongo/executor/connection_pool.cpp
index 631df12fe5d..7fcc7fe53dc 100644
--- a/src/mongo/executor/connection_pool.cpp
+++ b/src/mongo/executor/connection_pool.cpp
@@ -98,6 +98,13 @@ public:
      */
     size_t createdConnections(const stdx::unique_lock<stdx::mutex>& lk);
 
+    /**
+     * Returns the total number of connections currently open that belong to
+     * this pool. This is the sum of refreshingConnections, availableConnections,
+     * and inUseConnections.
+     */
+    size_t openConnections(const stdx::unique_lock<stdx::mutex>& lk);
+
 private:
     using OwnedConnection = std::unique_ptr<ConnectionInterface>;
     using OwnershipPool = std::unordered_map<ConnectionInterface*, OwnedConnection>;
@@ -229,6 +236,16 @@ void ConnectionPool::appendConnectionStats(ConnectionPoolStats* stats) const {
     }
 }
 
+size_t ConnectionPool::getNumConnectionsPerHost(const HostAndPort& hostAndPort) const {
+    stdx::unique_lock<stdx::mutex> lk(_mutex);
+    auto iter = _pools.find(hostAndPort);
+    if (iter != _pools.end()) {
+        return iter->second->openConnections(lk);
+    }
+
+    return 0;
+}
+
 void ConnectionPool::returnConnection(ConnectionInterface* conn) {
     stdx::unique_lock<stdx::mutex> lk(_mutex);
 
@@ -266,6 +283,10 @@ size_t ConnectionPool::SpecificPool::createdConnections(const stdx::unique_lock<
     return _created;
 }
 
+size_t ConnectionPool::SpecificPool::openConnections(const stdx::unique_lock<stdx::mutex>& lk) {
+    return _checkedOutPool.size() + _readyPool.size() + _processingPool.size();
+}
+
 void ConnectionPool::SpecificPool::getConnection(const HostAndPort& hostAndPort,
                                                  Milliseconds timeout,
                                                  stdx::unique_lock<stdx::mutex> lk,
diff --git a/src/mongo/executor/connection_pool.h b/src/mongo/executor/connection_pool.h
index 83dbe54d240..ffa5495602f 100644
--- a/src/mongo/executor/connection_pool.h
+++ b/src/mongo/executor/connection_pool.h
@@ -121,6 +121,8 @@ public:
 
     void appendConnectionStats(ConnectionPoolStats* stats) const;
 
+    size_t getNumConnectionsPerHost(const HostAndPort& hostAndPort) const;
+
 private:
     void returnConnection(ConnectionInterface* connection);
 
@@ -190,7 +192,6 @@ class ConnectionPool::ConnectionInterface : public TimerInterface {
 
 public:
     ConnectionInterface() = default;
-
     virtual ~ConnectionInterface() = default;
 
     /**
diff --git a/src/mongo/executor/network_interface_asio_command.cpp b/src/mongo/executor/network_interface_asio_command.cpp
index 6a4677d4dfa..57b77298b42 100644
--- a/src/mongo/executor/network_interface_asio_command.cpp
+++ b/src/mongo/executor/network_interface_asio_command.cpp
@@ -235,9 +235,11 @@ void NetworkInterfaceASIO::_beginCommunication(AsyncOp* op) {
     // codepath.
 
     if (op->_inSetup) {
+        auto host = op->request().target;
         auto getConnectionDuration = now() - op->start();
-        log() << "Successfully connected to " << op->request().target.toString() << ", took "
-              << getConnectionDuration;
+        log() << "Successfully connected to " << host << ", took " << getConnectionDuration << " ("
+              << _connectionPool.getNumConnectionsPerHost(host) << " connections now open to "
+              << host << ")";
         op->_inSetup = false;
         op->finish(RemoteCommandResponse());
         return;