PYTHON-3005 Make maxConnecting configurable (#789)

Author: ShaneHarvey

doc/changelog.rst

@@ -185,6 +185,8 @@ Notable improvements
 
 - Enhanced connection pooling to create connections more efficiently and
   avoid connection storms.
+- Added the ``maxConnecting`` URI and
+  :class:`~pymongo.mongo_client.MongoClient` keyword argument.
 - :class:`~pymongo.mongo_client.MongoClient` now accepts a URI and keyword
   argument `srvMaxHosts` that limits the number of mongos-like hosts a client
   will connect to. More specifically, when a mongodb+srv:// connection string

pymongo/client_options.py

@@ -138,6 +138,7 @@ def _parse_pool_options(options):
         options.get('zlibcompressionlevel', -1))
     ssl_context, tls_allow_invalid_hostnames = _parse_ssl_options(options)
     load_balanced = options.get('loadbalanced')
+    max_connecting = options.get('maxconnecting', common.MAX_CONNECTING)
     return PoolOptions(max_pool_size,
                        min_pool_size,
                        max_idle_time_seconds,
@@ -148,6 +149,7 @@ def _parse_pool_options(options):
                        appname,
                        driver,
                        compression_settings,
+                       max_connecting=max_connecting,
                        server_api=server_api,
                        load_balanced=load_balanced)
 

pymongo/common.py

@@ -615,6 +615,7 @@ def validate_auto_encryption_opts_or_none(option, value):
     'journal': validate_boolean_or_string,
     'localthresholdms': validate_positive_float_or_zero,
     'maxidletimems': validate_timeout_or_none,
+    'maxconnecting': validate_positive_integer,
     'maxpoolsize': validate_non_negative_integer_or_none,
     'maxstalenessseconds': validate_max_staleness,
     'readconcernlevel': validate_string_or_none,

pymongo/mongo_client.py

@@ -216,6 +216,8 @@ def __init__(
           - `maxIdleTimeMS` (optional): The maximum number of milliseconds that
             a connection can remain idle in the pool before being removed and
             replaced. Defaults to `None` (no limit).
+          - `maxConnecting` (optional): The maximum number of connections that
+            each pool can establish concurrently. Defaults to `2`.
           - `socketTimeoutMS`: (integer or None) Controls how long (in
             milliseconds) the driver will wait for a response after sending an
             ordinary (non-monitoring) database operation before concluding that
@@ -506,7 +508,8 @@ def __init__(
            arguments.
            The default for `uuidRepresentation` was changed from
            ``pythonLegacy`` to ``unspecified``.
-           Added the ``srvServiceName`` URI and keyword argument.
+           Added the ``srvServiceName`` and ``maxConnecting`` URI and keyword
+           argument.
 
         .. versionchanged:: 3.12
            Added the ``server_api`` keyword argument.

test/cmap/pool-checkout-custom-maxConnecting-is-enforced.json

@@ -0,0 +1,81 @@
+{
+  "version": 1,
+  "style": "integration",
+  "description": "custom maxConnecting is enforced",
+  "runOn": [
+    {
+      "minServerVersion": "4.4.0"
+    }
+  ],
+  "failPoint": {
+    "configureFailPoint": "failCommand",
+    "mode": "alwaysOn",
+    "data": {
+      "failCommands": [
+        "isMaster",
+        "hello"
+      ],
+      "closeConnection": false,
+      "blockConnection": true,
+      "blockTimeMS": 500
+    }
+  },
+  "poolOptions": {
+    "maxConnecting": 1,
+    "maxPoolSize": 2,
+    "waitQueueTimeoutMS": 5000
+  },
+  "operations": [
+    {
+      "name": "ready"
+    },
+    {
+      "name": "start",
+      "target": "thread1"
+    },
+    {
+      "name": "start",
+      "target": "thread2"
+    },
+    {
+      "name": "checkOut",
+      "thread": "thread1"
+    },
+    {
+      "name": "waitForEvent",
+      "event": "ConnectionCreated",
+      "count": 1
+    },
+    {
+      "name": "checkOut",
+      "thread": "thread2"
+    },
+    {
+      "name": "waitForEvent",
+      "event": "ConnectionReady",
+      "count": 2
+    }
+  ],
+  "events": [
+    {
+      "type": "ConnectionCreated"
+    },
+    {
+      "type": "ConnectionReady"
+    },
+    {
+      "type": "ConnectionCreated"
+    },
+    {
+      "type": "ConnectionReady"
+    }
+  ],
+  "ignore": [
+    "ConnectionCheckOutStarted",
+    "ConnectionCheckedIn",
+    "ConnectionCheckedOut",
+    "ConnectionClosed",
+    "ConnectionPoolCreated",
+    "ConnectionPoolReady"
+  ]
+}

test/uri_options/connection-pool-options.json

@@ -2,15 +2,16 @@
   "tests": [
     {
       "description": "Valid connection pool options are parsed correctly",
-      "uri": "mongodb://example.com/?maxIdleTimeMS=50000&maxPoolSize=5&minPoolSize=3",
+      "uri": "mongodb://example.com/?maxIdleTimeMS=50000&maxPoolSize=5&minPoolSize=3&maxConnecting=1",
       "valid": true,
       "warning": false,
       "hosts": null,
       "auth": null,
       "options": {
         "maxIdleTimeMS": 50000,
         "maxPoolSize": 5,
-        "minPoolSize": 3
+        "minPoolSize": 3,
+        "maxConnecting": 1
       }
     },
     {
@@ -52,6 +53,24 @@
       "options": {
         "minPoolSize": 0
       }
+    },
+    {
+      "description": "maxConnecting=0 causes a warning",
+      "uri": "mongodb://example.com/?maxConnecting=0",
+      "valid": true,
+      "warning": true,
+      "hosts": null,
+      "auth": null,
+      "options": {}
+    },
+    {
+      "description": "maxConnecting<0 causes a warning",
+      "uri": "mongodb://example.com/?maxConnecting=-1",
+      "valid": true,
+      "warning": true,
+      "hosts": null,
+      "auth": null,
+      "options": {}
     }
   ]
 }