Revert "PYTHON-2970 Prioritize electionId over setVersion for stale primary check (#845)"

This reverts commit 52d7795.

Author: ShaneHarvey

doc/changelog.rst

@@ -12,8 +12,6 @@ PyMongo 3.13 drops support for Python 3.4.
 Bug fixes
 .........
 
-- Fixed a bug where the client could be unable to discover the new primary
-  after a simultaneous replica set election and reconfig (`PYTHON-2970`_).
 - Fixed a memory leak bug when calling :func:`~bson.decode_all` without a
   ``codec_options`` argument (`PYTHON-3222`_).
 - Fixed a bug where :func:`~bson.decode_all` did not accept ``codec_options``
@@ -29,7 +27,6 @@ Deprecations
 See the `PyMongo 3.13.0 release notes in JIRA`_ for the list of resolved issues
 in this release.
 
-.. _PYTHON-2970: https://jira.mongodb.org/browse/PYTHON-2970
 .. _PYTHON-3222: https://jira.mongodb.org/browse/PYTHON-3222
 .. _PyMongo 3.13.0 release notes in JIRA: https://jira.mongodb.org/secure/ReleaseNote.jspa?projectId=10004&version=31570
 

pymongo/collection.py

@@ -3109,8 +3109,6 @@ def map_reduce(self, map, reduce, out, full_response=False, session=None, **kwar
 
            - https://docs.mongodb.com/manual/reference/map-reduce-to-aggregation-pipeline/
            - https://docs.mongodb.com/manual/reference/aggregation-commands-comparison/
-
-           .. _mapReduce command: https://docs.mongodb.com/manual/reference/command/mapReduce/
         .. versionchanged:: 3.4
            Added the `collation` option.
         .. versionchanged:: 2.2
@@ -3119,7 +3117,6 @@ def map_reduce(self, map, reduce, out, full_response=False, session=None, **kwar
         .. _map reduce command: http://docs.mongodb.org/manual/reference/command/mapReduce/
 
         .. seealso:: The MongoDB documentation on `mapreduce <https://dochub.mongodb.org/core/mapreduce>`_.
-
         """
         warnings.warn(
             'map_reduce is deprecated, use aggregate instead',
@@ -3183,7 +3180,7 @@ def inline_map_reduce(self, map, reduce, full_response=False, session=None, **kw
         .. versionchanged:: 3.4
            Added the `collation` option.
 
-        .. _mapReduce command: https://docs.mongodb.com/manual/reference/command/mapReduce/
+        .. _map reduce command: http://docs.mongodb.org/manual/reference/command/mapReduce/
         """
         warnings.warn(
             'inline_map_reduce is deprecated, use aggregate instead',

pymongo/topology_description.py

@@ -16,7 +16,6 @@
 
 from collections import namedtuple
 
-from bson.min_key import MinKey
 from pymongo import common
 from pymongo.errors import ConfigurationError
 from pymongo.read_preferences import ReadPreference
@@ -495,16 +494,24 @@ def _update_rs_from_primary(
         sds.pop(server_description.address)
         return (_check_has_primary(sds), replica_set_name, max_set_version, max_election_id)
 
-    new_election_tuple = server_description.election_id, server_description.set_version
-    max_election_tuple = max_election_id, max_set_version
-    new_election_safe = tuple(MinKey() if i is None else i for i in new_election_tuple)
-    max_election_safe = tuple(MinKey() if i is None else i for i in max_election_tuple)
-    if new_election_safe >= max_election_safe:
-        max_election_id, max_set_version = new_election_tuple
-    else:
-        # Stale primary, set to type Unknown.
-        sds[server_description.address] = server_description.to_unknown()
-        return _check_has_primary(sds), replica_set_name, max_set_version, max_election_id
+    max_election_tuple = max_set_version, max_election_id
+    if None not in server_description.election_tuple:
+        if (
+            None not in max_election_tuple
+            and max_election_tuple > server_description.election_tuple
+        ):
+
+            # Stale primary, set to type Unknown.
+            sds[server_description.address] = server_description.to_unknown()
+            return (_check_has_primary(sds), replica_set_name, max_set_version, max_election_id)
+
+        max_election_id = server_description.election_id
+
+    if server_description.set_version is not None and (
+        max_set_version is None or server_description.set_version > max_set_version
+    ):
+
+        max_set_version = server_description.set_version
 
     # We've heard from the primary. Is it the same primary as before?
     for server in sds.values():

test/discovery_and_monitoring/rs/electionId_precedence_setVersion.json

@@ -120,18 +120,15 @@
       "outcome": {
         "servers": {
           "a:27017": {
-            "type": "Unknown",
-            "setName": null,
-            "setVersion": null,
-            "electionId": null
-          },
-          "b:27017": {
             "type": "RSPrimary",
             "setName": "rs",
             "setVersion": 1,
-            "electionId": {
-              "$oid": "000000000000000000000002"
-            }
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
           },
           "c:27017": {
             "type": "Unknown",
@@ -173,18 +170,15 @@
       "outcome": {
         "servers": {
           "a:27017": {
-            "type": "Unknown",
-            "setName": null,
-            "setVersion": null,
-            "electionId": null
-          },
-          "b:27017": {
             "type": "RSPrimary",
             "setName": "rs",
             "setVersion": 1,
-            "electionId": {
-              "$oid": "000000000000000000000002"
-            }
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
           },
           "c:27017": {
             "type": "Unknown",

test/discovery_and_monitoring/rs/null_election_id.json

@@ -1,5 +1,5 @@
 {
-  "description": "Secondary ignored when ok is zero",
+  "description": "New primary",
   "uri": "mongodb://a,b/?replicaSet=rs",
   "phases": [
     {