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

This reverts commit 225d131.

Author: ShaneHarvey

doc/changelog.rst

@@ -4,40 +4,33 @@ Changelog
 Changes in Version 4.1
 ----------------------
 
+.. warning:: PyMongo 4.1 drops support for Python 3.6.0 and 3.6.1, Python 3.6.2+ is now required.
+
 PyMongo 4.1 brings a number of improvements including:
 
-- :meth:`pymongo.collection.Collection.update_one`,
-  :meth:`pymongo.collection.Collection.update_many`,
-  :meth:`pymongo.collection.Collection.delete_one`,
-  :meth:`pymongo.collection.Collection.delete_many`,
-  :meth:`pymongo.collection.Collection.aggregate`,
-  :meth:`pymongo.collection.Collection.find_one_and_delete`,
-  :meth:`pymongo.collection.Collection.find_one_and_replace`,
-  :meth:`pymongo.collection.Collection.find_one_and_update`,
-  :meth:`pymongo.collection.Collection.find`,
-  and :meth:`pymongo.collection.Collection.replace_one `all support a new
-  keyword argument ``let`` which is a map of parameter names and values.
+- Added support for the ``let`` parameter to
+  :meth:`~pymongo.collection.Collection.update_one`,
+  :meth:`~pymongo.collection.Collection.update_many`,
+  :meth:`~pymongo.collection.Collection.delete_one`,
+  :meth:`~pymongo.collection.Collection.delete_many`,
+  :meth:`~pymongo.collection.Collection.replace_one`,
+  :meth:`~pymongo.collection.Collection.aggregate`,
+  :meth:`~pymongo.collection.Collection.find_one_and_delete`,
+  :meth:`~pymongo.collection.Collection.find_one_and_replace`,
+  :meth:`~pymongo.collection.Collection.find_one_and_update`,
+  :meth:`~pymongo.collection.Collection.find`,
+  :meth:`~pymongo.collection.Collection.find_one`,
+  and :meth:`~pymongo.collection.Collection.bulk_write`.
+  ``let`` is a map of parameter names and values.
   Parameters can then be accessed as variables in an aggregate expression
   context.
 - :meth:`~pymongo.collection.Collection.aggregate` now supports
   $merge and $out executing on secondaries on MongoDB >=5.0.
   aggregate() now always obeys the collection's :attr:`read_preference` on
   MongoDB >= 5.0.
-- :meth:`gridfs.GridOut.seek` now returns the new position in the file, to
+- :meth:`gridfs.grid_file.GridOut.seek` now returns the new position in the file, to
   conform to the behavior of :meth:`io.IOBase.seek`.
 
-Breaking Changes in 4.1
-.......................
-- Removed support for Python 3.6.0 and 3.6.1, Python 3.6.2+ is now required.
-
-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`_).
-
-.. _PYTHON-2970: https://jira.mongodb.org/browse/PYTHON-2970
-
 Issues Resolved
 ...............
 

pymongo/topology_description.py

@@ -17,7 +17,6 @@
 from random import sample
 from typing import Any, Callable, Dict, List, NamedTuple, Optional, Tuple
 
-from bson.min_key import MinKey
 from bson.objectid import ObjectId
 from pymongo import common
 from pymongo.errors import ConfigurationError
@@ -532,16 +531,24 @@ 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

@@ -123,18 +123,15 @@
       "outcome": {
         "servers": {
           "a:27017": {
-            "type": "Unknown",
-            "setName": null,
-            "setVersion": null,
-            "electionId": null
-          },
-          "b:27017": {
             "type": "RSPrimary",
             "setName": "rs",
             "setVersion": 1,
-            "electionId": {
-              "$oid": "000000000000000000000002"
-            }
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
           },
           "c:27017": {
             "type": "Unknown",
@@ -177,18 +174,15 @@
       "outcome": {
         "servers": {
           "a:27017": {
-            "type": "Unknown",
-            "setName": null,
-            "setVersion": null,
-            "electionId": null
-          },
-          "b:27017": {
             "type": "RSPrimary",
             "setName": "rs",
             "setVersion": 1,
-            "electionId": {
-              "$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": [
     {