JAVA-2069: Use both setVersion and electionId to detect a stale primary

src/main/com/mongodb/BaseCluster.java

@@ -197,6 +197,10 @@ protected void fireChangeEvent() {
         clusterListener.clusterDescriptionChanged(new ClusterDescriptionChangedEvent(clusterId, description));
     }
 
+    ClusterDescription getCurrentDescription() {
+        return description;
+    }
+
     // gets a random server that still exists in the cluster.  Returns null if there are none.
     private ClusterableServer getRandomServer(final List<ServerDescription> serverDescriptions) {
         while (!serverDescriptions.isEmpty()) {

src/main/com/mongodb/MultiServerCluster.java

@@ -45,6 +45,7 @@ final class MultiServerCluster extends BaseCluster {
     private ClusterType clusterType;
     private String replicaSetName;
     private ObjectId maxElectionId;
+    private Integer maxSetVersion;
     private final ConcurrentMap<ServerAddress, ServerTuple> addressToServerTupleMap =
     new ConcurrentHashMap<ServerAddress, ServerTuple>();
 
@@ -201,10 +202,13 @@ private boolean handleReplicaSetMemberChanged(final ServerDescription newDescrip
         }
 
         if (newDescription.isPrimary()) {
-            if (newDescription.getElectionId() != null) {
-                if (maxElectionId != null && maxElectionId.compareTo(newDescription.getElectionId()) > 0) {
-                    LOGGER.info(format("Invalidating potential primary %s whose election id %s is less than the max election id seen so "
-                            + "far %s", newDescription.getAddress(), newDescription.getElectionId(), maxElectionId));
+            if (newDescription.getSetVersion() != null && newDescription.getElectionId() != null) {
+                if (isStalePrimary(newDescription)) {
+                    LOGGER.info(format("Invalidating potential primary %s whose (set version, election id) tuple of (%d, %s) "
+                                    + "is less than one already seen of (%d, %s)",
+                            newDescription.getAddress(),
+                            newDescription.getSetVersion(), newDescription.getElectionId(),
+                            maxSetVersion, maxElectionId));
                     addressToServerTupleMap.get(newDescription.getAddress()).server.invalidate();
                     return false;
                 }
@@ -216,6 +220,13 @@ private boolean handleReplicaSetMemberChanged(final ServerDescription newDescrip
                 }
             }
 
+            if (newDescription.getSetVersion() != null
+                    && (maxSetVersion == null || newDescription.getSetVersion().compareTo(maxSetVersion) > 0)) {
+                LOGGER.info(format("Setting max set version to %d from replica set primary %s", newDescription.getSetVersion(),
+                        newDescription.getAddress()));
+                maxSetVersion = newDescription.getSetVersion();
+            }
+
             if (isNotAlreadyPrimary(newDescription.getAddress())) {
                 LOGGER.info(format("Discovered replica set primary %s", newDescription.getAddress()));
             }
@@ -224,6 +235,15 @@ private boolean handleReplicaSetMemberChanged(final ServerDescription newDescrip
         return true;
     }
 
+    private boolean isStalePrimary(final ServerDescription newDescription) {
+        if (maxSetVersion == null || maxElectionId == null) {
+            return false;
+        }
+
+        return (maxSetVersion.compareTo(newDescription.getSetVersion()) > 0
+                || (maxSetVersion.equals(newDescription.getSetVersion()) && maxElectionId.compareTo(newDescription.getElectionId()) > 0));
+    }
+
     private boolean isNotAlreadyPrimary(final ServerAddress address) {
         ServerTuple serverTuple = addressToServerTupleMap.get(address);
         return serverTuple == null || !serverTuple.description.isPrimary();

src/main/com/mongodb/ServerDescription.java

@@ -74,6 +74,7 @@ class ServerDescription {
     private final int maxWireVersion;
 
     private final ObjectId electionId;
+    private final Integer setVersion;
 
     private final Throwable exception;
 
@@ -97,6 +98,7 @@ static class Builder {
         private int minWireVersion = 0;
         private int maxWireVersion = 0;
         private ObjectId electionId;
+        private Integer setVersion;
         private Throwable exception;
 
         // CHECKSTYLE:OFF
@@ -202,6 +204,17 @@ public Builder electionId(final ObjectId electionId) {
             return this;
         }
 
+        /**
+         * Sets the setVersion reported by this server.
+         *
+         * @param setVersion the set version
+         * @return this
+         */
+        public Builder setVersion(final Integer setVersion) {
+            this.setVersion = setVersion;
+            return this;
+        }
+
         public Builder exception(final Throwable exception) {
             this.exception = exception;
             return this;
@@ -343,6 +356,15 @@ public ObjectId getElectionId() {
         return electionId;
     }
 
+    /**
+     * The replica set setVersion reported by this MongoDB server.
+     *
+     * @return the setVersion, which may be null
+     */
+    public Integer getSetVersion() {
+        return setVersion;
+    }
+
     /**
      * Returns true if the server has the given tags.  A server of either type {@code ServerType.StandAlone} or
      * {@code ServerType.ShardRouter} is considered to have all tags, so this method will always return true for instances of either of
@@ -467,7 +489,9 @@ public boolean equals(final Object o) {
         if (electionId != null ? !electionId.equals(that.electionId) : that.electionId != null) {
             return false;
         }
-
+        if (setVersion != null ? !setVersion.equals(that.setVersion) : that.setVersion != null) {
+            return false;
+        }
         // Compare class equality and message as exceptions rarely override equals
         Class thisExceptionClass = exception != null ? exception.getClass() : null;
         Class thatExceptionClass = that.exception != null ? that.exception.getClass() : null;
@@ -505,6 +529,7 @@ public int hashCode() {
         result = 31 * result + minWireVersion;
         result = 31 * result + maxWireVersion;
         result = 31 * result + (electionId != null ? electionId.hashCode() : 0);
+        result = 31 * result + (setVersion != null ? setVersion.hashCode() : 0);
         result = 31 * result + (exception == null ? 0 : exception.getClass().hashCode());
         result = 31 * result + (exception == null ? 0 : exception.getMessage().hashCode());
         return result;
@@ -524,6 +549,7 @@ public String toString() {
                + ", maxMessageSize=" + maxMessageSize
                + ", maxWriteBatchSize=" + maxWriteBatchSize
                + ", electionId=" + electionId
+               + ", setVersion=" + setVersion
                + ", tagSet=" + tagSet
                + ", setName='" + setName + '\''
                + ", averageLatencyNanos=" + averageLatencyNanos
@@ -587,6 +613,7 @@ private String getAverageLatencyFormattedInMilliseconds() {
         minWireVersion = builder.minWireVersion;
         maxWireVersion = builder.maxWireVersion;
         electionId = builder.electionId;
+        setVersion = builder.setVersion;
         exception = builder.exception;
     }
 }

src/main/com/mongodb/ServerMonitor.java

@@ -239,8 +239,8 @@ private ServerDescription lookupServerDescription(final DBPort connection) throw
     }
 
     @SuppressWarnings("unchecked")
-    private ServerDescription createDescription(final CommandResult commandResult, final ServerVersion serverVersion,
-                                                final long averageLatencyNanos) {
+    ServerDescription createDescription(final CommandResult commandResult, final ServerVersion serverVersion,
+                                        final long averageLatencyNanos) {
         return ServerDescription.builder()
                                 .state(ServerConnectionState.Connected)
                                 .version(serverVersion)
@@ -260,6 +260,7 @@ private ServerDescription createDescription(final CommandResult commandResult, f
                                 .minWireVersion(commandResult.getInt("minWireVersion", ServerDescription.getDefaultMinWireVersion()))
                                 .maxWireVersion(commandResult.getInt("maxWireVersion", ServerDescription.getDefaultMaxWireVersion()))
                                 .electionId(commandResult.containsKey("electionId") ? commandResult.getObjectId("electionId") : null)
+                                .setVersion(commandResult.containsKey("setVersion") ? commandResult.getInt("setVersion") : null)
                                 .averageLatency(averageLatencyNanos, TimeUnit.NANOSECONDS)
                                 .ok(commandResult.ok()).build();
     }

src/test/com/mongodb/MultiServerClusterSpecification.groovy

@@ -510,23 +510,24 @@ class MultiServerClusterSpecification extends Specification {
 
     def sendNotification(ServerAddress serverAddress, ServerType serverType, List<ServerAddress> hosts, String setName,
                          ServerAddress trueAddress) {
-        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], true, setName, null, trueAddress)
-                                                                  .build())
+        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], true, setName, null, null,
+                trueAddress).build())
     }
 
     def sendNotification(ServerAddress serverAddress, ServerType serverType, List<ServerAddress> hosts, List<ServerAddress> passives,
                          String setName) {
-        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, passives, true, setName, null, null)
-                                                                  .build())
+        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, passives, true, setName, null, null,
+                null).build())
     }
 
     def sendNotification(ServerAddress serverAddress, ServerType serverType, List<ServerAddress> hosts, ObjectId electionId) {
-        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], true, 'test', electionId, null)
-                                                                  .build())
+        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], true, 'test', 2, electionId,
+                null).build())
     }
 
     def sendNotification(ServerAddress serverAddress, ServerType serverType, List<ServerAddress> hosts, boolean ok) {
-        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], ok, null, null, null).build())
+        factory.getServer(serverAddress).sendNotification(getBuilder(serverAddress, serverType, hosts, [], ok, null, null, null, null)
+                .build())
     }
 
     def getClusterDescription(MultiServerCluster cluster) {
@@ -542,7 +543,7 @@ class MultiServerClusterSpecification extends Specification {
     }
 
     def getBuilder(ServerAddress serverAddress, ServerType serverType, List<ServerAddress> hosts, List<ServerAddress> passives, boolean ok,
-                   String setName, ObjectId electionId, ServerAddress trueAddress) {
+                   String setName, Integer setVersion, ObjectId electionId, ServerAddress trueAddress) {
         ServerDescription.builder()
                          .address(serverAddress)
                          .type(serverType)
@@ -553,5 +554,6 @@ class MultiServerClusterSpecification extends Specification {
                          .passives(passives*.toString() as Set)
                          .setName(setName)
                          .electionId(electionId)
+                         .setVersion(setVersion)
     }
 }

src/test/com/mongodb/ServerDescriptionTest.java

@@ -88,6 +88,7 @@ public void testDefaults() throws UnknownHostException {
         assertEquals(0, serverDescription.getMinWireVersion());
         assertEquals(0, serverDescription.getMaxWireVersion());
         assertNull(serverDescription.getElectionId());
+        assertNull(serverDescription.getSetVersion());
         assertNull(serverDescription.getException());
     }
 
@@ -117,6 +118,7 @@ public void testBuilder() throws UnknownHostException {
                                               .minWireVersion(1)
                                               .maxWireVersion(2)
                                               .electionId(new ObjectId("123412341234123412341234"))
+                                              .setVersion(2)
                                               .exception(exception)
                                               .build();
 
@@ -151,6 +153,7 @@ public void testBuilder() throws UnknownHostException {
         assertEquals(1, serverDescription.getMinWireVersion());
         assertEquals(2, serverDescription.getMaxWireVersion());
         assertEquals(new ObjectId("123412341234123412341234"), serverDescription.getElectionId());
+        assertEquals(new Integer(2), serverDescription.getSetVersion());
         assertEquals(exception, serverDescription.getException());
     }
 
@@ -176,6 +179,7 @@ public void testObjectOverrides() throws UnknownHostException {
                                             .minWireVersion(1)
                                             .maxWireVersion(2)
                                             .electionId(new ObjectId())
+                                            .setVersion(2)
                                             .exception(new IllegalArgumentException("This is illegal"));
         assertEquals(builder.build(), builder.build());
         assertEquals(builder.build().hashCode(), builder.build().hashCode());

src/test/com/mongodb/ServerMonitorSpecification.groovy

@@ -72,6 +72,19 @@ class ServerMonitorSpecification extends FunctionalSpecification {
         newDescription.electionId == expected
     }
 
+    def 'should set setVersion'() {
+        given:
+        initializeServerMonitor(new ServerAddress())
+        CommandResult commandResult = database.command(new BasicDBObject('ismaster', 1))
+        def expected = commandResult.get('setVersion')
+
+        when:
+        latch.await()
+
+        then:
+        newDescription.setVersion == expected
+    }
+
     @IgnoreIf( { serverIsAtLeastVersion(2.6) } )
     def 'should set default max wire batch size when not provided by server'() {
         given: