JAVA-2389: Allow smallest max staleness check to proceed if cluster type is replica set, even when there are no available servers

Author: jyemin

driver-core/src/main/com/mongodb/TaggableReadPreference.java

@@ -20,7 +20,6 @@
 import com.mongodb.connection.ClusterDescription;
 import com.mongodb.connection.ClusterType;
 import com.mongodb.connection.ServerDescription;
-import com.mongodb.connection.ServerType;
 import org.bson.BsonArray;
 import org.bson.BsonDocument;
 import org.bson.BsonInt64;
@@ -35,7 +34,6 @@
 import static com.mongodb.assertions.Assertions.notNull;
 import static java.lang.String.format;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
-import static java.util.concurrent.TimeUnit.NANOSECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
 /**
@@ -186,10 +184,6 @@ protected List<ServerDescription> selectFreshServers(final ClusterDescription cl
             return servers;
         }
 
-        if (servers.isEmpty()) {
-            return servers;
-        }
-
         long heartbeatFrequencyMS = clusterDescription.getServerSettings().getHeartbeatFrequency(MILLISECONDS);
 
         if (getMaxStaleness(MILLISECONDS) < Math.max(SMALLEST_MAX_STALENESS_MS, heartbeatFrequencyMS + IDLE_WRITE_PERIOD_MS)) {
@@ -229,22 +223,6 @@ protected List<ServerDescription> selectFreshServers(final ClusterDescription cl
         return freshServers;
     }
 
-    private ServerDescription getMostUpToDateServerDescription(final ClusterDescription clusterDescription) {
-        ServerDescription mostUpToDateServerDescription = null;
-        for (ServerDescription cur : clusterDescription.getServerDescriptions()) {
-            if (cur.getType() == ServerType.REPLICA_SET_PRIMARY) {
-                mostUpToDateServerDescription = cur;
-                break;
-            } else if (cur.getType() == ServerType.REPLICA_SET_SECONDARY) {
-                if (mostUpToDateServerDescription == null
-                            || cur.getLastUpdateTime(NANOSECONDS) > mostUpToDateServerDescription.getLastUpdateTime(NANOSECONDS)) {
-                    mostUpToDateServerDescription = cur;
-                }
-            }
-        }
-        return mostUpToDateServerDescription;
-    }
-
     private long getStalenessOfSecondaryRelativeToPrimary(final ServerDescription primary, final ServerDescription serverDescription,
                                                           final long heartbeatFrequencyMS) {
         return primary.getLastWriteDate().getTime()

driver-core/src/test/resources/max-staleness/server_selection/ReplicaSetNoPrimary/NoKnownServers.json

@@ -1,10 +1,9 @@
 {
-    "in_latency_window": [],
+    "error": true,
     "read_preference": {
         "maxStalenessSeconds": 1,
         "mode": "Nearest"
     },
-    "suitable_servers": [],
     "topology_description": {
         "servers": [
             {

driver-core/src/test/resources/max-staleness/server_selection/ReplicaSetNoPrimary/ZeroMaxStaleness.json

@@ -0,0 +1,36 @@
+{
+    "error": true,
+    "read_preference": {
+        "maxStalenessSeconds": 0,
+        "mode": "Nearest"
+    },
+    "topology_description": {
+        "servers": [
+            {
+                "address": "a:27017",
+                "avg_rtt_ms": 5,
+                "lastUpdateTime": 0,
+                "lastWrite": {
+                    "lastWriteDate": {
+                        "$numberLong": "2"
+                    }
+                },
+                "maxWireVersion": 5,
+                "type": "RSSecondary"
+            },
+            {
+                "address": "b:27017",
+                "avg_rtt_ms": 5,
+                "lastUpdateTime": 0,
+                "lastWrite": {
+                    "lastWriteDate": {
+                        "$numberLong": "1"
+                    }
+                },
+                "maxWireVersion": 4,
+                "type": "RSSecondary"
+            }
+        ],
+        "type": "ReplicaSetNoPrimary"
+    }
+}

driver-core/src/test/resources/max-staleness/server_selection/ReplicaSetWithPrimary/LongHeartbeat2.json

@@ -18,6 +18,18 @@
                 },
                 "maxWireVersion": 5,
                 "type": "RSPrimary"
+            },
+            {
+                "address": "b:27017",
+                "avg_rtt_ms": 5,
+                "lastUpdateTime": 0,
+                "lastWrite": {
+                    "lastWriteDate": {
+                        "$numberLong": "1"
+                    }
+                },
+                "maxWireVersion": 5,
+                "type": "RSSecondary"
             }
         ],
         "type": "ReplicaSetWithPrimary"

driver-core/src/test/resources/max-staleness/server_selection/ReplicaSetWithPrimary/ZeroMaxStaleness.json

@@ -0,0 +1,36 @@
+{
+    "error": true,
+    "read_preference": {
+        "maxStalenessSeconds": 0,
+        "mode": "Nearest"
+    },
+    "topology_description": {
+        "servers": [
+            {
+                "address": "a:27017",
+                "avg_rtt_ms": 5,
+                "lastUpdateTime": 0,
+                "lastWrite": {
+                    "lastWriteDate": {
+                        "$numberLong": "2"
+                    }
+                },
+                "maxWireVersion": 5,
+                "type": "RSPrimary"
+            },
+            {
+                "address": "b:27017",
+                "avg_rtt_ms": 5,
+                "lastUpdateTime": 0,
+                "lastWrite": {
+                    "lastWriteDate": {
+                        "$numberLong": "1"
+                    }
+                },
+                "maxWireVersion": 4,
+                "type": "RSSecondary"
+            }
+        ],
+        "type": "ReplicaSetWithPrimary"
+    }
+}