PYTHON-1592 Remove Collection.parallel_scan (#547)

Author: ShaneHarvey

doc/api/pymongo/collection.rst

@@ -68,7 +68,6 @@
       .. automethod:: options
       .. automethod:: map_reduce
       .. automethod:: inline_map_reduce
-      .. automethod:: parallel_scan
       .. automethod:: initialize_unordered_bulk_op
       .. automethod:: initialize_ordered_bulk_op
       .. automethod:: group

doc/changelog.rst

@@ -15,13 +15,14 @@ Breaking Changes in 4.0
 .......................
 
 - Removed support for Python 2.7, 3.4, and 3.5. Python 3.6+ is now required.
-- Removed :meth:`~pymongo.database.Database.eval`,
-  :data:`~pymongo.database.Database.system_js` and
-  :class:`~pymongo.database.SystemJS`.
+- Removed :meth:`pymongo.database.Database.eval`,
+  :data:`pymongo.database.Database.system_js` and
+  :class:`pymongo.database.SystemJS`.
 - Removed :meth:`pymongo.mongo_client.MongoClient.fsync`,
   :meth:`pymongo.mongo_client.MongoClient.unlock`, and
   :attr:`pymongo.mongo_client.MongoClient.is_locked`.
-- Removed :mod:`~pymongo.thread_util`.
+- Removed :meth:`pymongo.collection.Collection.parallel_scan`.
+- Removed :mod:`pymongo.thread_util`.
 
 Notable improvements
 ....................

doc/migrate-to-pymongo4.rst

@@ -116,3 +116,12 @@ can be changed to this::
 
   >>> from bson.code import Code
   >>> result = database.command('eval', Code('function (x) {return x;}'), args=[3]).get('retval')
+
+
+Collection.parallel_scan is removed
+...................................
+
+Removed :meth:`~pymongo.collection.Collection.parallel_scan`. MongoDB 4.2
+removed the `parallelCollectionScan command`_.  There is no replacement.
+
+.. _parallelCollectionScan command: https://docs.mongodb.com/manual/reference/command/parallelCollectionScan/

pymongo/collection.py

@@ -1559,93 +1559,6 @@ def find_raw_batches(self, *args, **kwargs):
 
         return RawBatchCursor(self, *args, **kwargs)
 
-    def parallel_scan(self, num_cursors, session=None, **kwargs):
-        """**DEPRECATED**: Scan this entire collection in parallel.
-
-        Returns a list of up to ``num_cursors`` cursors that can be iterated
-        concurrently. As long as the collection is not modified during
-        scanning, each document appears once in one of the cursors result
-        sets.
-
-        For example, to process each document in a collection using some
-        thread-safe ``process_document()`` function:
-
-          >>> def process_cursor(cursor):
-          ...     for document in cursor:
-          ...     # Some thread-safe processing function:
-          ...     process_document(document)
-          >>>
-          >>> # Get up to 4 cursors.
-          ...
-          >>> cursors = collection.parallel_scan(4)
-          >>> threads = [
-          ...     threading.Thread(target=process_cursor, args=(cursor,))
-          ...     for cursor in cursors]
-          >>>
-          >>> for thread in threads:
-          ...     thread.start()
-          >>>
-          >>> for thread in threads:
-          ...     thread.join()
-          >>>
-          >>> # All documents have now been processed.
-
-        The :meth:`parallel_scan` method obeys the :attr:`read_preference` of
-        this :class:`Collection`.
-
-        :Parameters:
-          - `num_cursors`: the number of cursors to return
-          - `session` (optional): a
-            :class:`~pymongo.client_session.ClientSession`.
-          - `**kwargs`: additional options for the parallelCollectionScan
-            command can be passed as keyword arguments.
-
-        .. note:: Requires server version **>= 2.5.5**.
-
-        .. versionchanged:: 3.7
-           Deprecated.
-
-        .. versionchanged:: 3.6
-           Added ``session`` parameter.
-
-        .. versionchanged:: 3.4
-           Added back support for arbitrary keyword arguments. MongoDB 3.4
-           adds support for maxTimeMS as an option to the
-           parallelCollectionScan command.
-
-        .. versionchanged:: 3.0
-           Removed support for arbitrary keyword arguments, since
-           the parallelCollectionScan command has no optional arguments.
-        """
-        warnings.warn("parallel_scan is deprecated. MongoDB 4.2 will remove "
-                      "the parallelCollectionScan command.",
-                      DeprecationWarning, stacklevel=2)
-        cmd = SON([('parallelCollectionScan', self.__name),
-                   ('numCursors', num_cursors)])
-        cmd.update(kwargs)
-
-        with self._socket_for_reads(session) as (sock_info, slave_ok):
-            # We call sock_info.command here directly, instead of
-            # calling self._command to avoid using an implicit session.
-            result = sock_info.command(
-                self.__database.name,
-                cmd,
-                slave_ok,
-                self._read_preference_for(session),
-                self.codec_options,
-                read_concern=self.read_concern,
-                parse_write_concern_error=True,
-                session=session,
-                client=self.__database.client)
-
-        cursors = []
-        for cursor in result['cursors']:
-            cursors.append(CommandCursor(
-                self, cursor['cursor'], sock_info.address,
-                session=session, explicit_session=session is not None))
-
-        return cursors
-
     def _count(self, cmd, collation=None, session=None):
         """Internal count helper."""
         # XXX: "ns missing" checks can be removed when we drop support for

test/test_collection.py

@@ -1737,52 +1737,6 @@ def test_aggregation_cursor_alive(self):
 
             self.assertTrue(cursor.alive)
 
-    @client_context.require_no_mongos
-    @client_context.require_version_max(4, 1, 0)
-    @ignore_deprecations
-    def test_parallel_scan(self):
-        db = self.db
-        db.drop_collection("test")
-        if client_context.has_secondaries:
-            # Test that getMore messages are sent to the right server.
-            db = self.client.get_database(
-                db.name,
-                read_preference=ReadPreference.SECONDARY,
-                write_concern=WriteConcern(w=self.w))
-
-        coll = db.test
-        coll.insert_many([{'_id': i} for i in range(8000)])
-        docs = []
-        threads = [threading.Thread(target=docs.extend, args=(cursor,))
-                   for cursor in coll.parallel_scan(3)]
-        for t in threads:
-            t.start()
-        for t in threads:
-            t.join()
-
-        self.assertEqual(
-            set(range(8000)),
-            set(doc['_id'] for doc in docs))
-
-    @client_context.require_no_mongos
-    @client_context.require_version_min(3, 3, 10)
-    @client_context.require_version_max(4, 1, 0)
-    @client_context.require_test_commands
-    @ignore_deprecations
-    def test_parallel_scan_max_time_ms(self):
-            self.client.admin.command("configureFailPoint",
-                                      "maxTimeAlwaysTimeOut",
-                                      mode="alwaysOn")
-            try:
-                self.assertRaises(ExecutionTimeout,
-                                  self.db.test.parallel_scan,
-                                  3,
-                                  maxTimeMS=1)
-            finally:
-                self.client.admin.command("configureFailPoint",
-                                          "maxTimeAlwaysTimeOut",
-                                          mode="off")
-
     def test_large_limit(self):
         db = self.db
         db.drop_collection("test_large_limit")

test/test_session.py

@@ -323,40 +323,6 @@ def test_collection(self):
 
         self._test_ops(client, *ops)
 
-    @client_context.require_no_mongos
-    @client_context.require_version_max(4, 1, 0)
-    @ignore_deprecations
-    def test_parallel_collection_scan(self):
-        listener = self.listener
-        client = self.client
-        coll = client.pymongo_test.collection
-        coll.insert_many([{'_id': i} for i in range(1000)])
-
-        listener.results.clear()
-
-        def scan(session=None):
-            cursors = coll.parallel_scan(4, session=session)
-            for c in cursors:
-                c.batch_size(2)
-                list(c)
-
-        listener.results.clear()
-        with client.start_session() as session:
-            scan(session)
-        cursor_lsids = {}
-        for event in listener.results['started']:
-            self.assertIn(
-                'lsid', event.command,
-                "parallel_scan sent no lsid with %s" % (event.command_name, ))
-
-            if event.command_name == 'getMore':
-                cursor_id = event.command['getMore']
-                if cursor_id in cursor_lsids:
-                    self.assertEqual(cursor_lsids[cursor_id],
-                                     event.command['lsid'])
-                else:
-                    cursor_lsids[cursor_id] = event.command['lsid']
-
     def test_cursor_clone(self):
         coll = self.client.pymongo_test.collection
         # Ensure some batches.
@@ -874,14 +840,6 @@ def test_reads(self):
                 lambda coll, session: coll.inline_map_reduce(
                     'function() {}', 'function() {}', session=session),
                 exception=map_reduce_exc)
-        if (not client_context.is_mongos and
-                not client_context.version.at_least(4, 1, 0)):
-            def scan(coll, session):
-                cursors = coll.parallel_scan(1, session=session)
-                for cur in cursors:
-                    list(cur)
-            self._test_reads(
-                lambda coll, session: scan(coll, session=session))
 
         self.assertRaises(
             ConfigurationError,