PYTHON-1864 PYTHON-2931 Spec complaint $readPreference (mongodb#809)

Stop sending $readPreference to standalone servers.
Stop sending $readPreference primary because it's the server default.
Remove outdated secondary_ok flag.

Author: ShaneHarvey

pymongo/aggregation.py

@@ -92,11 +92,6 @@ def _database(self):
         """The database against which the aggregation command is run."""
         raise NotImplementedError
 
-    def _process_result(self, result, session, server, sock_info, secondary_ok):
-        if self._result_processor:
-            self._result_processor(
-                result, session, server, sock_info, secondary_ok)
-
     def get_read_preference(self, session):
         if self._write_preference:
             return self._write_preference
@@ -105,7 +100,7 @@ def get_read_preference(self, session):
             self._write_preference = pref = _AggWritePref(pref)
         return pref
 
-    def get_cursor(self, session, server, sock_info, secondary_ok):
+    def get_cursor(self, session, server, sock_info, read_preference):
         # Serialize command.
         cmd = SON([("aggregate", self._aggregation_target),
                    ("pipeline", self._pipeline)])
@@ -134,8 +129,7 @@ def get_cursor(self, session, server, sock_info, secondary_ok):
         result = sock_info.command(
             self._database.name,
             cmd,
-            secondary_ok,
-            self.get_read_preference(session),
+            read_preference,
             self._target.codec_options,
             parse_write_concern_error=True,
             read_concern=read_concern,
@@ -145,7 +139,8 @@ def get_cursor(self, session, server, sock_info, secondary_ok):
             client=self._database.client,
             user_fields=self._user_fields)
 
-        self._process_result(result, session, server, sock_info, secondary_ok)
+        if self._result_processor:
+            self._result_processor(result, sock_info)
 
         # Extract cursor from result or mock/fake one if necessary.
         if 'cursor' in result:

pymongo/change_stream.py

@@ -148,7 +148,7 @@ def _aggregation_pipeline(self):
         full_pipeline.extend(self._pipeline)
         return full_pipeline
 
-    def _process_result(self, result, session, server, sock_info, secondary_ok):
+    def _process_result(self, result, sock_info):
         """Callback that caches the postBatchResumeToken or
         startAtOperationTime from a changeStream aggregate command response
         containing an empty batch of change documents.

pymongo/collection.py

@@ -186,7 +186,7 @@ def _socket_for_reads(self, session):
     def _socket_for_writes(self, session):
         return self.__database.client._socket_for_writes(session)
 
-    def _command(self, sock_info, command, secondary_ok=False,
+    def _command(self, sock_info, command,
                  read_preference=None,
                  codec_options=None, check=True, allowable_errors=None,
                  read_concern=None,
@@ -200,7 +200,6 @@ def _command(self, sock_info, command, secondary_ok=False,
         :Parameters:
           - `sock_info` - A SocketInfo instance.
           - `command` - The command itself, as a SON instance.
-          - `secondary_ok`: whether to set the secondaryOkay wire protocol bit.
           - `codec_options` (optional) - An instance of
             :class:`~bson.codec_options.CodecOptions`.
           - `check`: raise OperationFailure if there are errors
@@ -226,7 +225,6 @@ def _command(self, sock_info, command, secondary_ok=False,
             return sock_info.command(
                 self.__database.name,
                 command,
-                secondary_ok,
                 read_preference or self._read_preference_for(session),
                 codec_options or self.codec_options,
                 check,
@@ -1356,14 +1354,14 @@ def find_raw_batches(self, *args, **kwargs):
 
         return RawBatchCursor(self, *args, **kwargs)
 
-    def _count_cmd(self, session, sock_info, secondary_ok, cmd, collation):
+    def _count_cmd(self, session, sock_info, read_preference, cmd, collation):
         """Internal count command helper."""
         # XXX: "ns missing" checks can be removed when we drop support for
         # MongoDB 3.0, see SERVER-17051.
         res = self._command(
             sock_info,
             cmd,
-            secondary_ok,
+            read_preference=read_preference,
             allowable_errors=["ns missing"],
             codec_options=self.__write_response_codec_options,
             read_concern=self.read_concern,
@@ -1374,12 +1372,12 @@ def _count_cmd(self, session, sock_info, secondary_ok, cmd, collation):
         return int(res["n"])
 
     def _aggregate_one_result(
-            self, sock_info, secondary_ok, cmd, collation, session):
+            self, sock_info, read_preference, cmd, collation, session):
         """Internal helper to run an aggregate that returns a single result."""
         result = self._command(
             sock_info,
             cmd,
-            secondary_ok,
+            read_preference,
             allowable_errors=[26],  # Ignore NamespaceNotFound.
             codec_options=self.__write_response_codec_options,
             read_concern=self.read_concern,
@@ -1413,7 +1411,7 @@ def estimated_document_count(self, **kwargs):
             raise ConfigurationError(
                 'estimated_document_count does not support sessions')
 
-        def _cmd(session, server, sock_info, secondary_ok):
+        def _cmd(session, server, sock_info, read_preference):
             if sock_info.max_wire_version >= 12:
                 # MongoDB 4.9+
                 pipeline = [
@@ -1425,15 +1423,17 @@ def _cmd(session, server, sock_info, secondary_ok):
                            ('cursor', {})])
                 cmd.update(kwargs)
                 result = self._aggregate_one_result(
-                    sock_info, secondary_ok, cmd, collation=None, session=session)
+                    sock_info, read_preference, cmd, collation=None,
+                    session=session)
                 if not result:
                     return 0
                 return int(result['n'])
             else:
                 # MongoDB < 4.9
                 cmd = SON([('count', self.__name)])
                 cmd.update(kwargs)
-                return self._count_cmd(None, sock_info, secondary_ok, cmd, None)
+                return self._count_cmd(
+                    None, sock_info, read_preference, cmd, collation=None)
 
         return self.__database.client._retryable_read(
             _cmd, self.read_preference, None)
@@ -1506,9 +1506,9 @@ def count_documents(self, filter, session=None, **kwargs):
         collation = validate_collation_or_none(kwargs.pop('collation', None))
         cmd.update(kwargs)
 
-        def _cmd(session, server, sock_info, secondary_ok):
+        def _cmd(session, server, sock_info, read_preference):
             result = self._aggregate_one_result(
-                sock_info, secondary_ok, cmd, collation, session)
+                sock_info, read_preference, cmd, collation, session)
             if not result:
                 return 0
             return result['n']
@@ -1799,12 +1799,12 @@ def list_indexes(self, session=None):
         read_pref = ((session and session._txn_read_preference())
                      or ReadPreference.PRIMARY)
 
-        def _cmd(session, server, sock_info, secondary_ok):
+        def _cmd(session, server, sock_info, read_preference):
             cmd = SON([("listIndexes", self.__name), ("cursor", {})])
             with self.__database.client._tmp_session(session, False) as s:
                 try:
-                    cursor = self._command(sock_info, cmd, secondary_ok,
-                                           read_pref,
+                    cursor = self._command(sock_info, cmd,
+                                           read_preference,
                                            codec_options,
                                            session=s)["cursor"]
                 except OperationFailure as exc:
@@ -2220,9 +2220,10 @@ def distinct(self, key, filter=None, session=None, **kwargs):
             kwargs["query"] = filter
         collation = validate_collation_or_none(kwargs.pop('collation', None))
         cmd.update(kwargs)
-        def _cmd(session, server, sock_info, secondary_ok):
+        def _cmd(session, server, sock_info, read_preference):
             return self._command(
-                sock_info, cmd, secondary_ok, read_concern=self.read_concern,
+                sock_info, cmd, read_preference=read_preference,
+                read_concern=self.read_concern,
                 collation=collation, session=session,
                 user_fields={"values": 1})["values"]
 

pymongo/database.py

@@ -492,7 +492,7 @@ def watch(self, pipeline=None, full_document=None, resume_after=None,
             batch_size, collation, start_at_operation_time, session,
             start_after)
 
-    def _command(self, sock_info, command, secondary_ok=False, value=1, check=True,
+    def _command(self, sock_info, command, value=1, check=True,
                  allowable_errors=None, read_preference=ReadPreference.PRIMARY,
                  codec_options=DEFAULT_CODEC_OPTIONS,
                  write_concern=None,
@@ -506,7 +506,6 @@ def _command(self, sock_info, command, secondary_ok=False, value=1, check=True,
             return sock_info.command(
                 self.__name,
                 command,
-                secondary_ok,
                 read_preference,
                 codec_options,
                 check,
@@ -605,8 +604,8 @@ def command(self, command, value=1, check=True,
             read_preference = ((session and session._txn_read_preference())
                                or ReadPreference.PRIMARY)
         with self.__client._socket_for_reads(
-                read_preference, session) as (sock_info, secondary_ok):
-            return self._command(sock_info, command, secondary_ok, value,
+                read_preference, session) as (sock_info, read_preference):
+            return self._command(sock_info, command, value,
                                  check, allowable_errors, read_preference,
                                  codec_options, session=session, **kwargs)
 
@@ -618,16 +617,15 @@ def _retryable_read_command(self, command, value=1, check=True,
             read_preference = ((session and session._txn_read_preference())
                                or ReadPreference.PRIMARY)
 
-        def _cmd(session, server, sock_info, secondary_ok):
-            return self._command(sock_info, command, secondary_ok, value,
+        def _cmd(session, server, sock_info, read_preference):
+            return self._command(sock_info, command, value,
                                  check, allowable_errors, read_preference,
                                  codec_options, session=session, **kwargs)
 
         return self.__client._retryable_read(
             _cmd, read_preference, session)
 
-    def _list_collections(self, sock_info, secondary_okay, session,
-                          read_preference, **kwargs):
+    def _list_collections(self, sock_info, session, read_preference, **kwargs):
         """Internal listCollections helper."""
 
         coll = self.get_collection(
@@ -638,7 +636,7 @@ def _list_collections(self, sock_info, secondary_okay, session,
         with self.__client._tmp_session(
                 session, close=False) as tmp_session:
             cursor = self._command(
-                sock_info, cmd, secondary_okay,
+                sock_info, cmd,
                 read_preference=read_preference,
                 session=tmp_session)["cursor"]
             cmd_cursor = CommandCursor(
@@ -674,9 +672,9 @@ def list_collections(self, session=None, filter=None, **kwargs):
         read_pref = ((session and session._txn_read_preference())
                      or ReadPreference.PRIMARY)
 
-        def _cmd(session, server, sock_info, secondary_okay):
+        def _cmd(session, server, sock_info, read_preference):
             return self._list_collections(
-                sock_info, secondary_okay, session, read_preference=read_pref,
+                sock_info, session, read_preference=read_preference,
                 **kwargs)
 
         return self.__client._retryable_read(

pymongo/message.py

@@ -316,9 +316,9 @@ def as_command(self, sock_info):
         self._as_command = cmd, self.db
         return self._as_command
 
-    def get_message(self, set_secondary_ok, sock_info, use_cmd=False):
+    def get_message(self, read_preference, sock_info, use_cmd=False):
         """Get a query message, possibly setting the secondaryOk bit."""
-        if set_secondary_ok:
+        if read_preference.mode:
             # Set the secondaryOk bit.
             flags = self.flags | 4
         else:
@@ -330,8 +330,7 @@ def get_message(self, set_secondary_ok, sock_info, use_cmd=False):
         if use_cmd:
             spec = self.as_command(sock_info)[0]
             request_id, msg, size, _ = _op_msg(
-                0, spec, self.db, self.read_preference,
-                set_secondary_ok, self.codec_options,
+                0, spec, self.db, read_preference, self.codec_options,
                 ctx=sock_info.compression_context)
             return request_id, msg, size
 
@@ -346,8 +345,7 @@ def get_message(self, set_secondary_ok, sock_info, use_cmd=False):
                 ntoreturn = self.limit
 
         if sock_info.is_mongos:
-            spec = _maybe_add_read_preference(spec,
-                                              self.read_preference)
+            spec = _maybe_add_read_preference(spec, read_preference)
 
         return _query(flags, ns, self.ntoskip, ntoreturn,
                       spec, None if use_cmd else self.fields,
@@ -429,8 +427,7 @@ def get_message(self, dummy0, sock_info, use_cmd=False):
             else:
                 flags = 0
             request_id, msg, size, _ = _op_msg(
-                flags, spec, self.db, None,
-                False, self.codec_options,
+                flags, spec, self.db, None, self.codec_options,
                 ctx=sock_info.compression_context)
             return request_id, msg, size
 
@@ -572,16 +569,13 @@ def _op_msg_uncompressed(flags, command, identifier, docs, opts):
     _op_msg_uncompressed = _cmessage._op_msg
 
 
-def _op_msg(flags, command, dbname, read_preference, secondary_ok,
-            opts, ctx=None):
+def _op_msg(flags, command, dbname, read_preference, opts, ctx=None):
     """Get a OP_MSG message."""
     command['$db'] = dbname
     # getMore commands do not send $readPreference.
     if read_preference is not None and "$readPreference" not in command:
-        if secondary_ok and not read_preference.mode:
-            command["$readPreference"] = (
-                ReadPreference.PRIMARY_PREFERRED.document)
-        else:
+        # Only send $readPreference if it's not primary (the default).
+        if read_preference.mode:
             command["$readPreference"] = read_preference.document
     name = next(iter(command))
     try: