SERVER-7612 explicit primary read pref does not work well with shard versioning

Ensure that selectNodeUsingTags will use the same connection to the primary with checkMaster

4 files changed, 294 insertions, 81 deletions

diff --git a/jstests/sharding/read_pref_multi_mongos_stale_config.js b/jstests/sharding/read_pref_multi_mongos_stale_config.js
new file mode 100644
index 00000000000..1556adef9e8
--- /dev/null
+++ b/jstests/sharding/read_pref_multi_mongos_stale_config.js
@@ -0,0 +1,34 @@
+var st = new ShardingTest({ shards: { rs0: { quiet: '' }, rs1: { quiet: '' }}, mongos: 2 });
+
+var testDB1 = st.s0.getDB('test');
+var testDB2 = st.s1.getDB('test');
+
+// Trigger a query on mongos 1 so it will have a view of test.user as being unsharded.
+testDB1.user.findOne();
+
+testDB2.adminCommand({ enableSharding: 'test' });
+testDB2.adminCommand({ shardCollection: 'test.user', key: { x: 1 }});
+
+testDB2.adminCommand({ split: 'test.user', middle: { x: 100 }});
+
+var configDB2 = st.s1.getDB('config');
+var chunkToMove = configDB2.chunks.find().sort({ min: 1 }).next();
+var toShard = configDB2.shards.findOne({ _id: { $ne: chunkToMove.shard }})._id;
+testDB2.adminCommand({ moveChunk: 'test.user', to: toShard, find: { x: 50 }});
+
+for (var x = 0; x < 200; x++) {
+    testDB2.user.insert({ x: x });
+}
+
+testDB2.runCommand({ getLastError: 1 });
+
+var cursor = testDB1.user.find({ x: 30 }).readPref('primary');
+assert(cursor.hasNext());
+assert.eq(30, cursor.next().x);
+
+cursor = testDB1.user.find({ x: 130 }).readPref('primary');
+assert(cursor.hasNext());
+assert.eq(130, cursor.next().x);
+
+st.stop();
+
diff --git a/src/mongo/client/dbclient_rs.cpp b/src/mongo/client/dbclient_rs.cpp
index 657731c40f0..437f75bcf6a 100644
--- a/src/mongo/client/dbclient_rs.cpp
+++ b/src/mongo/client/dbclient_rs.cpp
@@ -46,15 +46,19 @@ namespace mongo {
      * @param lastHost the last host returned (mainly used for doing round-robin).
      *     Will be overwritten with the newly returned host if not empty. Should
      *     never be NULL.
+     * @param isPrimarySelected out parameter that is set to true if the returned host
+     *     is a primary.
      *
      * @return the host object of the node selected. If none of the nodes are
-     *     eligible, returns an empty host.
+     *     eligible, returns an empty host. Cannot be NULL and valid only if returned
+     *     host is not empty.
      */
     HostAndPort _selectNode(const vector<ReplicaSetMonitor::Node>& nodes,
                             const BSONObj& readPreferenceTag,
                             bool secOnly,
                             int localThresholdMillis,
-                            HostAndPort* lastHost /* in/out */) {
+                            HostAndPort* lastHost /* in/out */,
+                            bool* isPrimarySelected) {
         HostAndPort fallbackHost;
 
         // Implicit: start from index 0 if lastHost doesn't exist anymore
@@ -85,6 +89,7 @@ namespace mongo {
             if (node.matchesTag(readPreferenceTag)) {
                 // found an ok candidate; may not be local.
                 fallbackHost = node.addr;
+                *isPrimarySelected = node.ismaster;
 
                 if (node.isLocalSecondary(localThresholdMillis)) {
                     // found a local node.  return early.
@@ -1006,14 +1011,15 @@ namespace mongo {
     }
 
     HostAndPort ReplicaSetMonitor::selectAndCheckNode(ReadPreference preference,
-                                                      TagSet* tags) {
+                                                      TagSet* tags,
+                                                      bool* isPrimarySelected) {
 
         HostAndPort candidate;
 
         {
             scoped_lock lk(_lock);
             candidate = ReplicaSetMonitor::selectNode(_nodes, preference, tags,
-                    _localThresholdMillis, &_lastReadPrefHost);
+                    _localThresholdMillis, &_lastReadPrefHost, isPrimarySelected);
         }
 
         if (candidate.empty()) {
@@ -1022,7 +1028,7 @@ namespace mongo {
 
             scoped_lock lk(_lock);
             return ReplicaSetMonitor::selectNode(_nodes, preference, tags, _localThresholdMillis,
-                    &_lastReadPrefHost);
+                    &_lastReadPrefHost, isPrimarySelected);
         }
 
         return candidate;
@@ -1033,11 +1039,15 @@ namespace mongo {
                                               ReadPreference preference,
                                               TagSet* tags,
                                               int localThresholdMillis,
-                                              HostAndPort* lastHost) {
+                                              HostAndPort* lastHost,
+                                              bool* isPrimarySelected) {
+        *isPrimarySelected = false;
+
         switch (preference) {
         case ReadPreference_PrimaryOnly:
             for (vector<Node>::const_iterator iter = nodes.begin(); iter != nodes.end(); ++iter) {
                 if (iter->ismaster && iter->ok) {
+                    *isPrimarySelected = true;
                     return iter->addr;
                 }
             }
@@ -1047,14 +1057,14 @@ namespace mongo {
         case ReadPreference_PrimaryPreferred:
         {
             HostAndPort candidatePri = selectNode(nodes, ReadPreference_PrimaryOnly, tags,
-                                                  localThresholdMillis, lastHost);
+                    localThresholdMillis, lastHost, isPrimarySelected);
 
             if (!candidatePri.empty()) {
                 return candidatePri;
             }
 
             return selectNode(nodes, ReadPreference_SecondaryOnly, tags,
-                              localThresholdMillis, lastHost);
+                              localThresholdMillis, lastHost, isPrimarySelected);
         }
 
         case ReadPreference_SecondaryOnly:
@@ -1063,7 +1073,7 @@ namespace mongo {
 
             while (!tags->isExhausted()) {
                 candidate = _selectNode(nodes, tags->getCurrentTag(), true, localThresholdMillis,
-                        lastHost);
+                        lastHost, isPrimarySelected);
 
                 if (candidate.empty()) {
                     tags->next();
@@ -1079,14 +1089,14 @@ namespace mongo {
         case ReadPreference_SecondaryPreferred:
         {
             HostAndPort candidateSec = selectNode(nodes, ReadPreference_SecondaryOnly, tags,
-                                                  localThresholdMillis, lastHost);
+                    localThresholdMillis, lastHost, isPrimarySelected);
 
             if (!candidateSec.empty()) {
                 return candidateSec;
             }
 
             return selectNode(nodes, ReadPreference_PrimaryOnly, tags,
-                              localThresholdMillis, lastHost);
+                    localThresholdMillis, lastHost, isPrimarySelected);
         }
 
         case ReadPreference_Nearest:
@@ -1095,7 +1105,7 @@ namespace mongo {
 
             while (!tags->isExhausted()) {
                 candidate = _selectNode(nodes, tags->getCurrentTag(), false, localThresholdMillis,
-                        lastHost);
+                        lastHost, isPrimarySelected);
 
                 if (candidate.empty()) {
                     tags->next();
@@ -1559,12 +1569,24 @@ namespace mongo {
         }
 
         ReplicaSetMonitorPtr monitor = _getMonitor();
-        _lastSlaveOkHost = monitor->selectAndCheckNode(preference, tags);
+        bool isPrimarySelected = false;
+        _lastSlaveOkHost = monitor->selectAndCheckNode(preference, tags, &isPrimarySelected);
 
         if ( _lastSlaveOkHost.empty() ){
             return NULL;
         }
 
+        // Primary connection is special because it is the only connection that is
+        // versioned in mongos. Therefore, we have to make sure that this object
+        // maintains only one connection to the primary and use that connection
+        // every time we need to talk to the primary.
+        if (isPrimarySelected) {
+            checkMaster();
+            _lastSlaveOkConn = _master;
+            _lastSlaveOkHost = _masterHost; // implied, but still assign just to be safe
+            return _master.get();
+        }
+
         _lastSlaveOkConn.reset(new DBClientConnection(true , this , _so_timeout));
         _lastSlaveOkConn->connect(_lastSlaveOkHost);
 
diff --git a/src/mongo/client/dbclient_rs.h b/src/mongo/client/dbclient_rs.h
index 79d604384d8..1b21bae8876 100644
--- a/src/mongo/client/dbclient_rs.h
+++ b/src/mongo/client/dbclient_rs.h
@@ -147,6 +147,8 @@ namespace mongo {
          *     robin, starting from the node next to this lastHost. This will be overwritten
          *     with the newly chosen host if not empty, not primary and when preference
          *     is not Nearest.
+         * @param isPrimarySelected out parameter that is set to true if the returned host
+         *     is a primary. Cannot be NULL and valid only if returned host is not empty.
          *
          * @return the host object of the node selected. If none of the nodes are
          *     eligible, returns an empty host.
@@ -155,7 +157,8 @@ namespace mongo {
                                       ReadPreference preference,
                                       TagSet* tags,
                                       int localThresholdMillis,
-                                      HostAndPort* lastHost);
+                                      HostAndPort* lastHost,
+                                      bool* isPrimarySelected);
 
         /**
          * Selects the right node given the nodes to pick from and the preference. This
@@ -163,14 +166,17 @@ namespace mongo {
          * if the primary node needs to be returned but is not currently available (except
          * for ReadPrefrence_Nearest).
          *
-         * @param preference the read mode to use
-         * @param tags the tags used for filtering nodes
+         * @param preference the read mode to use.
+         * @param tags the tags used for filtering nodes.
+         * @param isPrimarySelected out parameter that is set to true if the returned host
+         *     is a primary. Cannot be NULL and valid only if returned host is not empty.
          *
          * @return the host object of the node selected. If none of the nodes are
          *     eligible, returns an empty host.
          */
         HostAndPort selectAndCheckNode(ReadPreference preference,
-                                       TagSet* tags);
+                                       TagSet* tags,
+                                       bool* isPrimarySelected);
 
         /**
          * Creates a new ReplicaSetMonitor, if it doesn't already exist.
@@ -270,6 +276,8 @@ namespace mongo {
          */
         bool isAnyNodeOk() const;
 
+        bool isHostPrimary(const std::string& hostName) const;
+
     private:
         /**
          * This populates a list of hosts from the list of seeds (discarding the
@@ -556,12 +564,18 @@ namespace mongo {
         string _setName;
 
         HostAndPort _masterHost;
-        scoped_ptr<DBClientConnection> _master;
+        // Note: reason why this is a shared_ptr is because we want _lastSlaveOkConn to
+        // keep a reference of the _master connection when it selected a primary node.
+        // This is because the primary connection is special in mongos - it is the only
+        // connection that is versioned.
+        // WARNING: do not assign this variable (which will increment the internal ref
+        // counter) to any other variable other than _lastSlaveOkConn.
+        boost::shared_ptr<DBClientConnection> _master;
 
         // Last used host in a slaveOk query (can be a primary)
         HostAndPort _lastSlaveOkHost;
         // Last used connection in a slaveOk query (can be a primary)
-        scoped_ptr<DBClientConnection> _lastSlaveOkConn;
+        boost::shared_ptr<DBClientConnection> _lastSlaveOkConn;
         
         double _so_timeout;
 
diff --git a/src/mongo/dbtests/replica_set_monitor_test.cpp b/src/mongo/dbtests/replica_set_monitor_test.cpp
index 717423b599e..e7965e35cda 100644
--- a/src/mongo/dbtests/replica_set_monitor_test.cpp
+++ b/src/mongo/dbtests/replica_set_monitor_test.cpp
@@ -369,8 +369,11 @@ namespace {
         TagSet tags(TagSetFixtures::getDefaultSet());
         HostAndPort lastHost = nodes[0].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
+        ASSERT(isPrimarySelected);
 
         ASSERT_EQUALS("b", host.host());
     }
@@ -383,9 +386,12 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3,  &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3,  &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT(host.empty());
     }
 
@@ -397,8 +403,10 @@ namespace {
 
         nodes[1].ismaster = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -410,9 +418,12 @@ namespace {
         TagSet tags(TagSetFixtures::getDefaultSet());
         HostAndPort lastHost = nodes[0].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 1, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -424,9 +435,12 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 1, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -439,9 +453,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryOnly, &tags, 1, &lastHost);
+            mongo::ReadPreference_SecondaryOnly, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -455,8 +472,10 @@ namespace {
         nodes[0].ok = false;
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryOnly, &tags, 1, &lastHost);
+            mongo::ReadPreference_SecondaryOnly, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -469,9 +488,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -485,9 +507,12 @@ namespace {
         nodes[0].ok = false;
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -502,8 +527,10 @@ namespace {
         nodes[1].ok = false;
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 1, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -518,9 +545,12 @@ namespace {
         nodes[1].pingTimeMillis = 2;
         nodes[2].pingTimeMillis = 3;
 
+        bool isPrimarySelected = 0;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -535,8 +565,10 @@ namespace {
         nodes[1].pingTimeMillis = 20;
         nodes[2].pingTimeMillis = 30;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(!host.empty());
     }
@@ -547,9 +579,12 @@ namespace {
         TagSet tags(TagSetFixtures::getP2Tag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         // Note: PrimaryOnly ignores tag
         ASSERT_EQUALS("b", host.host());
     }
@@ -562,8 +597,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
@@ -575,8 +612,10 @@ namespace {
         TagSet tags(TagSetFixtures::getSingleNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT_EQUALS("b", host.host());
     }
@@ -589,8 +628,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -601,9 +642,12 @@ namespace {
         TagSet tags(TagSetFixtures::getP2Tag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -617,8 +661,10 @@ namespace {
         arrayBuilder.append(BSON("dc" << "sf"));
         TagSet tags(arrayBuilder.arr());
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost);
+             mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost,
+             &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -629,8 +675,10 @@ namespace {
         TagSet tags(TagSetFixtures::getP2Tag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
@@ -647,9 +695,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -660,9 +711,12 @@ namespace {
         TagSet tags(TagSetFixtures::getSingleNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -674,8 +728,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -686,9 +742,12 @@ namespace {
         TagSet tags(TagSetFixtures::getSingleNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -701,9 +760,12 @@ namespace {
         arrayBuilder.append(BSON("p" << "1"));
         TagSet tags(arrayBuilder.arr());
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -714,8 +776,10 @@ namespace {
         TagSet tags(TagSetFixtures::getSingleNoMatchTag());
         HostAndPort lastHost = nodes[1].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -726,9 +790,12 @@ namespace {
         TagSet tags(TagSetFixtures::getMultiNoMatchTag());
         HostAndPort lastHost = nodes[1].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -741,8 +808,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryOnly, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -758,9 +827,12 @@ namespace {
         TagSet tags(arrayBuilder.arr());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -839,10 +911,12 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -854,10 +928,12 @@ namespace {
         nodes[0].ok = false;
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -868,10 +944,12 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -883,10 +961,12 @@ namespace {
         nodes[1].ok = false;
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -897,10 +977,12 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -912,9 +994,10 @@ namespace {
         nodes[0].ok = false;
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_PrimaryPreferred, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -926,9 +1009,12 @@ namespace {
         TagSet tags(TagSetFixtures::getMultiNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -940,8 +1026,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost);
+            mongo::ReadPreference_PrimaryPreferred, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -950,10 +1038,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -964,10 +1054,12 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -976,10 +1068,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -990,10 +1084,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1002,10 +1098,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1016,9 +1114,10 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryOnly, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -1028,10 +1127,12 @@ namespace {
                 NodeSetFixtures::getThreeMemberWithTags();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
              mongo::ReadPreference_SecondaryOnly, getMatchesPriTagSet(),
-             3, &lastHost);
+             3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1042,8 +1143,10 @@ namespace {
         TagSet tags(TagSetFixtures::getMultiNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost);
+             mongo::ReadPreference_SecondaryOnly, &tags, 3, &lastHost,
+             &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -1052,10 +1155,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1066,22 +1171,26 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
 
     TEST_F(MultiTags, SecPrefMatchesSecond) {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
-            HostAndPort lastHost = nodes[2].addr;
+        HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -1092,10 +1201,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesSecondTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1104,10 +1215,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1118,10 +1231,12 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_SecondaryPreferred, getMatchesLastTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -1129,10 +1244,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
              mongo::ReadPreference_SecondaryPreferred, getMatchesPriTagSet(),
-             3, &lastHost);
+             3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1143,9 +1260,12 @@ namespace {
         TagSet tags(TagSetFixtures::getMultiNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+             mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+             &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
     }
 
@@ -1157,8 +1277,10 @@ namespace {
 
         nodes[1].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost);
+             mongo::ReadPreference_SecondaryPreferred, &tags, 3, &lastHost,
+             &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -1167,10 +1289,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
             mongo::ReadPreference_Nearest, getMatchesFirstTagSet(),
-            3, &lastHost);
+            3, &lastHost, &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1187,9 +1311,12 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -1198,9 +1325,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, getMatchesSecondTagSet(), 3, &lastHost);
+            mongo::ReadPreference_Nearest, getMatchesSecondTagSet(), 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("c", host.host());
         ASSERT_EQUALS("c", lastHost.host());
     }
@@ -1218,9 +1348,12 @@ namespace {
 
         nodes[2].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+            mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -1229,9 +1362,12 @@ namespace {
         vector<ReplicaSetMonitor::Node> nodes = getNodes();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, getMatchesLastTagSet(), 3, &lastHost);
+            mongo::ReadPreference_Nearest, getMatchesLastTagSet(), 3, &lastHost,
+            &isPrimarySelected);
 
+        ASSERT(!isPrimarySelected);
         ASSERT_EQUALS("a", host.host());
         ASSERT_EQUALS("a", lastHost.host());
     }
@@ -1242,8 +1378,10 @@ namespace {
 
         nodes[0].ok = false;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-            mongo::ReadPreference_Nearest, getMatchesLastTagSet(), 3, &lastHost);
+            mongo::ReadPreference_Nearest, getMatchesLastTagSet(), 3, &lastHost,
+            &isPrimarySelected);
 
         ASSERT(host.empty());
     }
@@ -1253,9 +1391,12 @@ namespace {
                 NodeSetFixtures::getThreeMemberWithTags();
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_Nearest, getMatchesPriTagSet(), 3, &lastHost);
+             mongo::ReadPreference_Nearest, getMatchesPriTagSet(), 3, &lastHost,
+             &isPrimarySelected);
 
+        ASSERT(isPrimarySelected);
         ASSERT_EQUALS("b", host.host());
         ASSERT_EQUALS("b", lastHost.host());
     }
@@ -1266,8 +1407,10 @@ namespace {
         TagSet tags(TagSetFixtures::getMultiNoMatchTag());
         HostAndPort lastHost = nodes[2].addr;
 
+        bool isPrimarySelected = false;
         HostAndPort host = ReplicaSetMonitor::selectNode(nodes,
-             mongo::ReadPreference_Nearest, &tags, 3, &lastHost);
+             mongo::ReadPreference_Nearest, &tags, 3, &lastHost,
+             &isPrimarySelected);
 
         ASSERT(host.empty());
     }