5.0-compatibility.txt

====================================
Compatibility Changes in MongoDB 5.0
====================================

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The following 5.0 changes can affect compatibility with older
versions of MongoDB.

Certain Commands Only Accept Recognized Parameters
--------------------------------------------------

Starting in MongoDB 5.0, certain database commands raise an error if
passed a parameter not explicitly accepted by the command. In MongoDB
4.4 and earlier, unrecognized parameters are silently ignored.

Affected Commands:

- :dbcommand:`abortTransaction`
- :dbcommand:`aggregate`
- :dbcommand:`authenticate`
- :dbcommand:`collMod`
- :dbcommand:`commitTransaction`
- :dbcommand:`create`
- :dbcommand:`createIndexes`
- :dbcommand:`delete`
- :dbcommand:`drop`
- :dbcommand:`dropDatabase`
- :dbcommand:`dropIndexes`
- :dbcommand:`endSessions`
- :dbcommand:`explain`
- :dbcommand:`find`
- :dbcommand:`findAndModify`
- :dbcommand:`getMore`
- :dbcommand:`hello`
- :dbcommand:`insert`
- :dbcommand:`killCursors`
- :dbcommand:`listCollections`
- :dbcommand:`listDatabases`
- :dbcommand:`listIndexes`
- :dbcommand:`ping`
- :dbcommand:`refreshSessions`
- :dbcommand:`update`

Removed Commands
----------------

Starting in MongoDB 5.0, these database commands and
:binary:`~bin.mongo` shell helper methods are removed:

.. list-table::
   :header-rows: 1

   * - Removed Command
     - Alternative

   * - ``db.collection.copyTo()``
     - :pipeline:`$out`

   * - :method:`db.collection.ensureIndex()`
     - :method:`db.collection.createIndex()`

   * - ``db.collection.save()``
     - | :method:`db.collection.insertOne()`
       | :method:`db.collection.insertMany()`

   * - :method:`db.resetError()`
     - Not available

   * - :dbcommand:`geoSearch`
     - One of the :ref:`Geospatial Query Operators <geospatial-query-selectors>`

   * - ``Mongo.getSecondaryOk()``
     - :doc:`/reference/method/Mongo.getReadPrefMode`

   * - ``Mongo.isCausalConsistency``
     - Not available

   * - ``Mongo.setSecondaryOk()``
     -   :doc:`/reference/method/Mongo.setReadPref`

   * - ``rs.secondaryOk()``
     - :doc:`/reference/method/Mongo.setReadPref`

   * - :dbcommand:`resetError`
     - Not available

   * - :dbcommand:`shardConnPoolStats`
     - :dbcommand:`connPoolStats`

   * - :dbcommand:`unsetSharding`
     - Not available


Removed Parameters
------------------

.. include:: /includes/5.0-changes/removed-parameters.rst

Removed Index Types
-------------------

MongoDB 5.0 removes the deprecated :doc:`geoHaystack
</core/geohaystack>` index. Use a :doc:`2d index </core/2d>` instead.

Upgrading your MongoDB instance to 5.0 and setting
:ref:`featureCompatibilityVersion <view-fcv>` to ``5.0`` will delete any
pre-existing :doc:`geoHaystack </core/geohaystack>` indexes.

Removed Metrics
---------------

Starting in MongoDB 5.0, the :dbcommand:`serverStatus` command does not
output :serverstatus:`opReadConcernCounters`, which contained the
:ref:`read concern level <read-concern-levels>` specified by query
operations. Instead, the new :serverstatus:`readConcernCounters`
replaces :serverstatus:`opReadConcernCounters` and contains additional
information.

Starting in MongoDB 5.0, the :dbcommand:`serverStatus` command does not
output the ``cache pressure percentage threshold`` and the
``current cache pressure percentage`` under
``wiredTiger.snapshot-window-settings``.

Shell Changes
-------------

The ``mongo`` shell has been deprecated in MongoDB v5.0. The
replacement shell is :binary:`~bin.mongosh`.

Shell packaging also changes in MongoDB v5.0. Refer to the
:mongosh:`installation instructions </install>` for further details.

Replica Sets
------------

``enableMajorityReadConcern`` Is Not Configurable
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. include:: /includes/fact-eMRC-always-true-in-5.0.rst

.. include:: /includes/fact-psa-performance-issues.rst

``secondaryDelaySecs`` Configuration Setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Starting in MongoDB 5.0, :rsconf:`~members[n].secondaryDelaySecs`
replaces ``slaveDelay``. This change is not backwards compatible.

Non-transactional Reads on ``config.transactions``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. include:: /includes/fact-5.0-non-transactional-config-reads.rst

Manual Oplog Writes
~~~~~~~~~~~~~~~~~~~

Starting in MongoDB 5.0, it is no longer possible to perform manual
write operations to the :doc:`oplog </core/replica-set-oplog>` on a
cluster running as a :ref:`replica set <replication>`. Performing write
operations to the oplog when running as a
:term:`standalone instance <standalone>` should only be done with
guidance from MongoDB Support.

Automatic Reconfiguration for New Voting Replica Set Members
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. include:: /includes/extracts/initial-sync-semantics.rst

Removed Customizable Values For getLastErrorDefaults 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. include:: /includes/5.0-changes-getLastErrorDefaults-removed.rst


Read Concern ``snapshot`` on Capped Collections
-----------------------------------------------

.. include:: /includes/extracts/transactions-capped-collection-read-change.rst


``local`` is the Default Read Concern
-------------------------------------

Starting in MongoDB 5.0, :readconcern:`"local"` is the default read 
concern level for read operations against the primary and secondaries.

This may introduce a significant latency increase for count queries that 
use a filter and for :ref:`covered queries <covered-queries>`.

You can opt out of this behavior by setting the cluster-wide 
:ref:`read concern <read-concern>` with 
:dbcommand:`setDefaultRWConcern`.

New ``cursor.map()`` Return Type
--------------------------------

:method:`cursor.map()` returned an ``Array`` in the legacy
:binary:`~bin.mongo` shell. The return type is ``Cursor`` in
:binary:`~bin.mongosh`. You can use ``.toArray()`` to convert the
results. 

Update Operator Changes
-----------------------

Starting in MongoDB 5.0, :binary:`~bin.mongod` no longer raises
an error when you use the following update operators with an empty
operand expression ( ``{ }`` ):

- :update:`$addToSet`
- :update:`$bit`
- :update:`$currentDate`
- :update:`$inc`
- :update:`$max`
- :update:`$min`
- :update:`$mul`
- :update:`$pop`
- :update:`$pull`
- :update:`$pullAll`
- :update:`$push`
- :update:`$rename`
- :update:`$set`
- :update:`$setOnInsert`
- :update:`$unset`

An empty update results in no changes and no :term:`oplog` entry is
created (meaning that the operation is a no-op).

Aggregation Pipeline Operator Parameter Limits
----------------------------------------------

The following aggregation pipeline operators now have a 64-bit
integer value maximum limit.  

- :pipeline:`$sort`
- :pipeline:`$limit`

If you pass a value that exceeds this limit, the pipeline returns an 
invalid argument error.

``listDatabases`` Output Changes
--------------------------------

Starting in MongoDB 5.0, output from the :dbcommand:`listDatabases`
command running against a :binary:`~bin.mongod` is more consistent with
output from :dbcommand:`listDatabases` running against a
:binary:`~bin.mongos`.

The following table shows the differences in data types for
:dbcommand:`listDatabases` output fields between MongoDB 5.0 and earlier
versions. Only fields which differ between 5.0 and earlier versions are
listed.

.. list-table::
   :header-rows: 1
   :widths: 25 25 25 25

   * - Field

     - Type in MongoDB 5.0

     - Type in MongoDB 4.4 and earlier (``mongod``)

     - Type in MongoDB 4.4 and earlier (``mongos``)

   * - ``sizeOnDisk``

     - integer

     - double

     - integer

   * - ``totalSize``

     - integer

     - double

     - integer

   * - ``totalSizeMb``

     - integer

     - not present (see below)

     - integer

The output from :dbcommand:`listDatabases` now includes the
``totalSizeMb`` field when run against either a :binary:`~bin.mongos` or
a :binary:`~bin.mongod`. In MongoDB 4.4 and earlier, ``totalSizeMb``
only appears when run against :binary:`~bin.mongos`. ``totalSizeMb`` is
the sum of the ``sizeOnDisk`` fields, expressed in megabytes.

When run against :binary:`~bin.mongos`, the ``shards`` field in the
:dbcommand:`listDatabases` output contains a field-value pair for each
collection on a particular shard. Size values in the ``shards`` field
are expressed as integers.

Map-Reduce
----------

Starting in version 5.0, MongoDB deprecates the
:doc:`map-reduce</core/map-reduce>` operation.

For examples of aggregation pipeline alternatives to map-reduce
operations, see :doc:`/reference/map-reduce-to-aggregation-pipeline` and
:doc:`/tutorial/map-reduce-examples`.

Auditing
--------

MongoDB 5.0 adds auditing capabilities that can be configured at
runtime.

If ``auditLog.runtimeConfiguration`` is set to ``true``, then the
``mongod`` and ``mongos`` configuration files can no longer set
``setParameter.auditAuthorizationSuccess`` or
:doc:`configure audit filters
</tutorial/configure-audit-filters>`. If the server configuration files
contain these settings the server will fail to start and will log an
error.

If ``auditLog.runtimeConfiguration`` is set to ``false`` and an audit
filter config document is present, then a startup warning will be
issued but the server will not abort.

General Changes
---------------

Starting in MongoDB 5.0:

- For :ref:`featureCompatibilityVersion <view-fcv>` set to ``"5.0"`` or
  greater, users can no longer write directly to the
  :data:`<database>.system.views` collection.

- The :dbcommand:`reIndex` command and the
  :method:`db.collection.reIndex()` shell method may only be run on
  :term:`standalone` instances.

- The number of :doc:`aggregation pipeline stages
  </reference/operator/aggregation-pipeline>` allowed in a single
  pipeline is limited to 1000.

- Dropping the final collection in a database (or dropping the database
  itself) when :setting:`~storage.directoryPerDB` or
  :option:`--directoryperdb` is enabled deletes the newly empty
  subdirectory for that database.

- The :expression:`$subtract` aggregation operator will convert the data
  type of the result if necessary to accurately represent the result
  value. See :expression:`$subtract` for the specific conversions. This
  change also applies to MongoDB 4.4.3+, 4.2.12+, 4.0.22+, and 3.6.22+.

- MongoDB removes the ``--serviceExecutor`` command-line option and
  the corresponding ``net.serviceExecutor`` configuration option.

- You may not authenticate as multiple simultaneous users on the same
  client session if the :option:`--apiStrict` option is set. Attempting
  to authenticate as a new user while currently logged in as an existing
  user when the :option:`--apiStrict` option is set will generate an
  error message once per authentication attempt. If you are not using
  the :option:`--apiStrict` option, authenticating as a new user while
  currently logged in as an existing user will write a warning to the
  log once per authentication attempt.

- The :ref:`weights <specify-weights>` option is only allowed  for
  ``$text`` indexes. 

- You must explicitly set the global default
  :ref:`write concern <write-concern>` before attempting to reconfigure
  a :ref:`non-sharded <sharded-vs-non-sharded-collections>`
  :term:`replica set <replica set>` with a :doc:`configuration
  </reference/replica-configuration>` that would change the implicit
  default write concern. To set the global default write concern, use
  the :dbcommand:`setDefaultRWConcern` command.

- To set the ``replSetOplog`` size in :binary:`~bin.mongosh`, use the
  ``Double()`` constructor with the :dbcommand:`replSetResizeOplog`
  command.

Deprecations
~~~~~~~~~~~~

.. list-table::
   :widths: 20 80
   :header-rows: 1

   * - Deprecated

     - Description

   * - :binary:`~bin.mongo`

     - The legacy ``mongo`` shell has been deprecated in MongoDB v5.0. The
       replacement is :binary:`~bin.mongosh`.

   * - :method:`db.printSlaveReplicationInfo()`

     - .. include:: /includes/deprecated-db.printSlaveReplicationInfo.rst

   * - :method:`rs.printSlaveReplicationInfo()`

     - .. include:: /includes/deprecated-rs.printSlaveReplicationInfo.rst

   * - :setting:`security.clusterIpSourceWhitelist`

     - *Deprecated in version 5.0:* Use 
       :setting:`security.clusterIpSourceAllowlist` instead.

   * - :option:`--clusterIpSourceWhitelist`
       
     - *Deprecated in version 5.0:*  Use :option:`--clusterIpSourceAllowlist`
       instead.

   * - :dbcommand:`logout`

     - *Deprecated in version 5.0:* Disconnect from the server to end your
       session instead.

   * - :method:`db.logout()`

     - *Deprecated in version 5.0:* Disconnect from the server to end your
       session instead.

   * - :ref:`local <audit-message-local>` audit message field

     - *Deprecated in version 5.0:* Use the ``localEndpoint`` field in
       the :ref:`clientMetadata <audit-message-clientMetadata>` audit message
       instead.

.. _deprecated-wire-protocol-opcodes:

Deprecated Wire Protocol Opcodes
````````````````````````````````

MongoDB 5.0 deprecates the following
:ref:`wire protocol opcodes <mongodb-wire-protocol>`:

- ``OP_REPLY``
- ``OP_UPDATE``
- ``OP_INSERT``
- ``OP_QUERY``
- ``OP_GET_MORE``
- ``OP_DELETE``
- ``OP_KILL_CURSORS``

Newer driver versions use :ref:`OP_MSG <wire-op-msg>` instead of these
deprecated op codes. 

The related commands and methods are also deprecated in MongoDB 5.0:

- :dbcommand:`getLastError`
- :method:`db.getLastError()`
- :method:`db.getLastErrorObj()`

To ensure your driver uses the most up-to-date wire
protocol, upgrade your driver to a 5.0-compatible version.

Any code explicitly using :dbcommand:`getLastError`, 
:method:`db.getLastError()`, or :method:`db.getLastErrorObj()`  
should instead use the CRUD API to issue the write with
the desired :doc:`write concern </reference/write-concern>`. 
Information about the success or failure of the write operation will be 
provided directly by the driver as a return value.

.. _5.0-compatibility-enabled:

5.0 Feature Compatibility
-------------------------

Some features in 5.0 require not just the 5.0 binaries but the
:ref:`featureCompatibilityVersion <view-fcv>` (fCV) set to 5.0. These
features include:

- Creation of :ref:`time series collections
  <manual-timeseries-collection>` requires fCV set to 5.0+.

- Configuring Runtime Audit Filter Management requires fCV set to 5.0+.

- Usage of ``.`` and ``$`` in field names requires fCV set to 5.0+.

- :ref:`Resharding a collection <sharding-resharding>` requires fCV set
  to 5.0+.