DRIVERS-2412: add pre 6.0 condition to stale primary logic

source/server-discovery-and-monitoring/server-discovery-and-monitoring.rst

@@ -8,8 +8,8 @@ Server Discovery And Monitoring
 :Advisors: David Golden, Craig Wilson
 :Status: Accepted
 :Type: Standards
-:Version: 2.34
-:Last Modified: 2022-01-19
+:Version: 2.35
+:Last Modified: 2022-09-30
 
 .. contents::
 
@@ -1109,21 +1109,55 @@ updateRSFromPrimary
         return
 
     # Election ids are ObjectIds, see
-    # "using setVersion and electionId to detect stale primaries"
+    # "Using electionId and setVersion to detect stale primaries"
     # for comparison rules.
 
-    # Null values for both electionId and setVersion are always considered less than
-    if serverDescription.electionId > topologyDescription.maxElectionId or (
-        serverDescription.electionId == topologyDescription.maxElectionId
-        and serverDescription.setVersion >= topologyDescription.maxSetVersion
-    ):
-        topologyDescription.maxElectionId = serverDescription.electionId
-        topologyDescription.maxSetVersion = serverDescription.setVersion
+    if serverDescription.maxWireVersion >= 17:  # MongoDB 6.0+
+        # Null values for both electionId and setVersion are always considered less than
+        if serverDescription.electionId > topologyDescription.maxElectionId or (
+            serverDescription.electionId == topologyDescription.maxElectionId
+            and serverDescription.setVersion >= topologyDescription.maxSetVersion
+        ):
+            topologyDescription.maxElectionId = serverDescription.electionId
+            topologyDescription.maxSetVersion = serverDescription.setVersion
+        else:
+            # Stale primary.
+            # replace serverDescription with a default ServerDescription of type "Unknown"
+            checkIfHasPrimary()
+            return
     else:
-        # Stale primary.
-        # replace serverDescription with a default ServerDescription of type "Unknown"
-        checkIfHasPrimary()
-        return
+        # Maintain old comparison rules, namely setVersion is checked before electionId
+        # see "Using electionId and setVersion to detect stale primaries"
+        # for comparison rules.
+
+        if serverDescription.setVersion is not null and serverDescription.electionId is not null:
+            # Election ids are ObjectIds, see
+            # "using setVersion and electionId to detect stale primaries"
+            # for comparison rules.
+            if (
+                topologyDescription.maxSetVersion is not null
+                and topologyDescription.maxElectionId is not null
+                and (
+                    topologyDescription.maxSetVersion > serverDescription.setVersion
+                    or (
+                        topologyDescription.maxSetVersion == serverDescription.setVersion
+                        and topologyDescription.maxElectionId > serverDescription.electionId
+                    )
+                )
+            ):
+                # Stale primary.
+                # replace serverDescription with a default ServerDescription of type "Unknown"
+                checkIfHasPrimary()
+                return
+
+            topologyDescription.maxElectionId = serverDescription.electionId
+
+            if serverDescription.setVersion is not null and (
+                topologyDescription.maxSetVersion is null
+                or serverDescription.setVersion > topologyDescription.maxSetVersion
+            ):
+                topologyDescription.maxSetVersion = serverDescription.setVersion
+
 
     for each server in topologyDescription.servers:
         if server.address != serverDescription.address:
@@ -1986,10 +2020,16 @@ between the old and new primary during a split-brain period,
 and helps provide read-your-writes consistency with write concern "majority"
 and read preference "primary".
 
+Prior to MongoDB server version 6.0 drivers had the logic opposite from
+the server side Replica Set Management logic by ordering the tuple by ``setVersion`` before the ``electionId``.
+In order to remain compatibility with backup systems, etc. drivers continue to
+maintain the reversed logic when connected to a topology that reports a maxWireVersion less than ``17``.
+Server versions 6.0 and beyond MUST order the tuple by ``electionId`` then ``setVersion``.
+
 Requirements for read-your-writes consistency
 `````````````````````````````````````````````
 
-Using (setVersion, electionId) only provides read-your-writes consistency if:
+Using (electionId, setVersion) only provides read-your-writes consistency if:
 
 * The application uses the same MongoClient instance for write-concern
   "majority" writes and read-preference "primary" reads, and
@@ -2534,6 +2574,8 @@ mark the server Unknown and clear the pool.
 
 2022-07-11: Convert integration tests to the unified format.
 
+2022-30-09: Update ``updateRSFromPrimary`` to include logic before and after 6.0 servers
+
 .. Section for links.
 
 .. _hello or legacy hello: /source/mongodb-handshake/handshake.rst#terms

source/server-discovery-and-monitoring/tests/README.rst

@@ -150,6 +150,8 @@ All files in the "rs" directory include a connection string with a "replicaSet"
 Set the client's initial TopologyType to ReplicaSetNoPrimary.
 (For most clients, parsing a connection string with a "replicaSet" option
 automatically sets the TopologyType to ReplicaSetNoPrimary.)
+Some of the files in "rs" are post-fixed with "pre-6.0". These files test the ``updateRSFromPrimary`` behavior
+prior to maxWireVersion 17, there should be no special handling required for these tests.
 
 Set up a listener to collect SDAM events published by the client, including
 events published during client construction.

source/server-discovery-and-monitoring/tests/rs/electionId_precedence_setVersion.json

@@ -20,7 +20,7 @@
               "$oid": "000000000000000000000001"
             },
             "minWireVersion": 0,
-            "maxWireVersion": 6
+            "maxWireVersion": 17
           }
         ],
         [
@@ -39,7 +39,7 @@
               "$oid": "000000000000000000000001"
             },
             "minWireVersion": 0,
-            "maxWireVersion": 6
+            "maxWireVersion": 17
           }
         ],
         [
@@ -58,7 +58,7 @@
               "$oid": "000000000000000000000002"
             },
             "minWireVersion": 0,
-            "maxWireVersion": 6
+            "maxWireVersion": 17
           }
         ]
       ],

source/server-discovery-and-monitoring/tests/rs/electionId_precedence_setVersion.yml

@@ -14,7 +14,7 @@ phases:
           electionId:
             $oid: "000000000000000000000001"
           minWireVersion: 0
-          maxWireVersion: 6
+          maxWireVersion: 17
       - - "b:27017"
         - ok: 1
           helloOk: true
@@ -27,7 +27,7 @@ phases:
           electionId:
             $oid: "000000000000000000000001"
           minWireVersion: 0
-          maxWireVersion: 6
+          maxWireVersion: 17
       - - "a:27017"
         - ok: 1
           helloOk: true
@@ -40,7 +40,7 @@ phases:
           electionId:
             $oid: "000000000000000000000002"
           minWireVersion: 0
-          maxWireVersion: 6
+          maxWireVersion: 17
     outcome:
       servers:
         "a:27017":

source/server-discovery-and-monitoring/tests/rs/null_election_id-pre-6.0.json

@@ -0,0 +1,203 @@
+{
+  "description": "Pre 6.0 Primaries with and without electionIds",
+  "uri": "mongodb://a/?replicaSet=rs",
+  "phases": [
+    {
+      "responses": [
+        [
+          "a:27017",
+          {
+            "ok": 1,
+            "helloOk": true,
+            "isWritablePrimary": true,
+            "hosts": [
+              "a:27017",
+              "b:27017",
+              "c:27017"
+            ],
+            "setVersion": 1,
+            "setName": "rs",
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "RSPrimary",
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          },
+          "c:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          }
+        },
+        "topologyType": "ReplicaSetWithPrimary",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": "rs",
+        "maxSetVersion": 1
+      }
+    },
+    {
+      "responses": [
+        [
+          "b:27017",
+          {
+            "ok": 1,
+            "helloOk": true,
+            "isWritablePrimary": true,
+            "hosts": [
+              "a:27017",
+              "b:27017",
+              "c:27017"
+            ],
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": {
+              "$oid": "000000000000000000000002"
+            },
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "RSPrimary",
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": {
+              "$oid": "000000000000000000000002"
+            }
+          },
+          "c:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          }
+        },
+        "topologyType": "ReplicaSetWithPrimary",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": "rs",
+        "maxSetVersion": 1,
+        "maxElectionId": {
+          "$oid": "000000000000000000000002"
+        }
+      }
+    },
+    {
+      "responses": [
+        [
+          "a:27017",
+          {
+            "ok": 1,
+            "helloOk": true,
+            "isWritablePrimary": true,
+            "hosts": [
+              "a:27017",
+              "b:27017",
+              "c:27017"
+            ],
+            "setVersion": 1,
+            "setName": "rs",
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "RSPrimary",
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          },
+          "c:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          }
+        },
+        "topologyType": "ReplicaSetWithPrimary",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": "rs",
+        "maxSetVersion": 1,
+        "maxElectionId": {
+          "$oid": "000000000000000000000002"
+        }
+      }
+    },
+    {
+      "responses": [
+        [
+          "c:27017",
+          {
+            "ok": 1,
+            "helloOk": true,
+            "isWritablePrimary": true,
+            "hosts": [
+              "a:27017",
+              "b:27017",
+              "c:27017"
+            ],
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": {
+              "$oid": "000000000000000000000001"
+            },
+            "minWireVersion": 0,
+            "maxWireVersion": 6
+          }
+        ]
+      ],
+      "outcome": {
+        "servers": {
+          "a:27017": {
+            "type": "RSPrimary",
+            "setName": "rs",
+            "setVersion": 1,
+            "electionId": null
+          },
+          "b:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          },
+          "c:27017": {
+            "type": "Unknown",
+            "setName": null,
+            "electionId": null
+          }
+        },
+        "topologyType": "ReplicaSetWithPrimary",
+        "logicalSessionTimeoutMinutes": null,
+        "setName": "rs",
+        "maxSetVersion": 1,
+        "maxElectionId": {
+          "$oid": "000000000000000000000002"
+        }
+      }
+    }
+  ]
+}