PYTHON-926 - ReadPreference.NEAREST shouldn't pick arbiters.

pymongo/server_selectors.py

@@ -21,6 +21,10 @@ def any_server_selector(server_descriptions):
     return server_descriptions
 
 
+def readable_server_selector(server_descriptions):
+    return [s for s in server_descriptions if s.is_readable]
+
+
 def writable_server_selector(server_descriptions):
     return [s for s in server_descriptions if s.is_writable]
 
@@ -49,6 +53,11 @@ def single_tag_set_server_selector(tag_set, server_descriptions):
     A server tagged {'a': '1', 'b': '2'} matches the tag set {'a': '1'}.
 
     The empty tag set {} matches any server.
+
+    The `server_descriptions` passed to this function should have
+    non-readable servers (e.g. RSGhost, RSArbiter, Unknown) filtered
+    out (e.g. by readable_server_selector or secondary_server_selector)
+    first.
     """
     def tags_match(server_tags):
         for key, value in tag_set.items():
@@ -68,6 +77,11 @@ def tag_sets_server_selector(tag_sets, server_descriptions):
     [{'a': 'value'}, {}] expresses a preference for servers tagged
     {'a': 'value'}, but accepts any server if none matches the first
     preference.
+
+    The `server_descriptions` passed to this function should have
+    non-readable servers (e.g. RSGhost, RSArbiter, Unknown) filtered
+    out (e.g. by readable_server_selector or secondary_server_selector)
+    first.
     """
     for tag_set in tag_sets:
         selected = single_tag_set_server_selector(tag_set, server_descriptions)
@@ -81,6 +95,11 @@ def apply_local_threshold(latency_ms, server_descriptions):
     """All servers with round trip times within latency_ms of the fastest one.
 
     No ServerDescription's round_trip_time can be None.
+
+    The `server_descriptions` passed to this function should have
+    non-readable servers (e.g. RSGhost, RSArbiter, Unknown) filtered
+    out (e.g. by readable_server_selector or secondary_server_selector)
+    first.
     """
     if not server_descriptions:
         # Avoid ValueError from min() with empty sequence.
@@ -104,4 +123,5 @@ def secondary_with_tags_server_selector(tag_sets, server_descriptions):
 
 def member_with_tags_server_selector(tag_sets, server_descriptions):
     """All near-enough members matching the tag sets."""
-    return tag_sets_server_selector(tag_sets, server_descriptions)
+    return tag_sets_server_selector(
+        tag_sets, readable_server_selector(server_descriptions))

test/__init__.py

@@ -127,8 +127,13 @@ class ClientContext(object):
                 self.rs_client = pymongo.MongoClient(
                     pair, replicaSet=self.replica_set_name)
 
-                self.nodes = set([partition_node(node)
-                                  for node in self.ismaster.get('hosts', [])])
+                nodes = [partition_node(node)
+                         for node in self.ismaster.get('hosts', [])]
+                nodes.extend([partition_node(node)
+                              for node in self.ismaster.get('passives', [])])
+                nodes.extend([partition_node(node)
+                              for node in self.ismaster.get('arbiters', [])])
+                self.nodes = set(nodes)
 
             self.rs_or_standalone_client = self.rs_client or self.client
 

test/test_read_preferences.py

@@ -31,7 +31,7 @@ from pymongo.read_preferences import (ReadPreference, MovingAverage,
                                       Primary, PrimaryPreferred,
                                       Secondary, SecondaryPreferred,
                                       Nearest, _ServerMode)
-from pymongo.server_selectors import any_server_selector
+from pymongo.server_selectors import readable_server_selector
 from pymongo.server_type import SERVER_TYPE
 from pymongo.write_concern import WriteConcern
 
@@ -97,7 +97,7 @@ class TestReadPreferencesBase(TestReplicaSetClientBase):
     def assertReadsFrom(self, expected, **kwargs):
         c = rs_client(**kwargs)
         wait_until(
-            lambda: len(c.nodes) == self.w,
+            lambda: len(c.nodes - c.arbiters) == self.w,
             "discovered all nodes")
 
         used = self.read_from_which_kind(c)
@@ -249,7 +249,8 @@ class TestReadPreferences(TestReadPreferencesBase):
         latencies = ', '.join(
             '%s: %dms' % (server.description.address,
                           server.description.round_trip_time)
-            for server in c._get_topology().select_servers(any_server_selector))
+            for server in c._get_topology().select_servers(
+                readable_server_selector))
 
         self.assertFalse(
             not_used,