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Release Notes for MongoDB 2.2
.. default-domain:: mongodb
MongoDB 2.2 is a production release series and succeeds the 2.0
production release series.
MongoDB 2.0 data files are compatible with 2.2-series binaries without any
special migration process. However, always perform the upgrade process for replica
sets and sharded clusters using the procedures that follow.
- :program:`mongod`, 2.2 is a drop-in replacement for 2.0 and 1.8.
- Check your :doc:`driver </applications/drivers>` documentation for
information regarding required compatibility upgrades, and always
run the recent release of your driver.
Typically, only users running with authentication, will need to
upgrade drivers before continuing with the upgrade to 2.2.
- For all deployments using authentication, upgrade the
drivers (i.e. client libraries), before upgrading the
:program:`mongod` instance or instances.
- For all upgrades of sharded clusters:
- turn off the balancer during the upgrade process. See the
:ref:`sharding-balancing-disable-temporarily` section for more
- upgrade all :program:`mongos` instances before upgrading any
:program:`mongod` instances.
Other than the above restrictions, 2.2 processes can interoperate with
2.0 and 1.8 tools and processes. You can safely upgrade the
:program:`mongod` and :program:`mongos` components of a deployment
one by one while the deployment is otherwise operational. Be sure to
read the detailed upgrade procedures below before upgrading production
.. [#secondaries-first] To minimize the interruption caused by
:ref:`election process <replica-set-elections>`, always upgrade the
secondaries of the set first, then :dbcommand:`step down
<replSetStepDown>` the primary, and then upgrade the primary.
.. _2.2-upgrade-standalone:
Upgrading a Standalone ``mongod``
#. Download binaries of the latest release in the 2.2 series from the
`MongoDB Download Page`_.
#. Shutdown your :program:`mongod` instance. Replace the existing
binary with the 2.2 :program:`mongod` binary and restart MongoDB.
.. _`MongoDB Download Page`:
.. _2.2-upgrade-replica-set:
Upgrading a Replica Set
You can upgrade to 2.2 by performing a "rolling"
upgrade of the set by upgrading the members individually while the
other members are available to minimize downtime. Use the following
#. Upgrade the :term:`secondary` members of the set one at a time by
shutting down the :program:`mongod` and replacing the 2.0 binary
with the 2.2 binary. After upgrading a :program:`mongod` instance,
wait for the member to recover to ``SECONDARY`` state
before upgrading the next instance.
To check the member's state, issue :method:`rs.status()` in the
:program:`mongo` shell.
#. Use the :program:`mongo` shell method :method:`rs.stepDown()` to
step down the :term:`primary` to allow the normal :ref:`failover
<replica-set-failover>` procedure. :method:`rs.stepDown()`
expedites the failover procedure and is preferable to shutting down
the primary directly.
Once the primary has stepped down and another member has assumed
``PRIMARY`` state, as observed in the output of
:method:`rs.status()`, shut down the previous primary and replace
:program:`mongod` binary with the 2.2 binary and start the new
.. note:: Replica set failover is not instant but will
render the set unavailable to read or accept writes
until the failover process completes. Typically this takes
10 seconds or more. You may wish to plan the upgrade during
a predefined maintenance window.
.. _2.2-upgrade-shard-cluster:
.. _2.2-upgrade-sharded-cluster:
Upgrading a Sharded Cluster
Use the following procedure to upgrade a sharded cluster:
- :ref:`Disable the balancer <sharding-balancing-disable-temporarily>`.
- Upgrade all :program:`mongos` instances *first*, in any order.
- Upgrade all of the :program:`mongod` config server instances
using the :ref:`stand alone <2.2-upgrade-standalone>` procedure.
To keep the cluster online, be sure that at all times at least one config
server is up.
- Upgrade each shard's replica set, using the :ref:`upgrade
procedure for replica sets <2.2-upgrade-replica-set>` detailed above.
- re-enable the balancer.
.. note::
Balancing is not currently supported in *mixed* 2.0.x and 2.2.0
deployments. Thus you will want to reach a consistent version for all
shards within a reasonable period of time, e.g. same-day.
See :issue:`SERVER-6902` for more information.
Major Features
Aggregation Framework
The aggregation framework makes it possible to do aggregation
operations without needing to use :term:`map-reduce`. The
:dbcommand:`aggregate` command exposes the aggregation framework, and the
:method:`~db.collection.aggregate()` helper in the :program:`mongo` shell
provides an interface to these operations. Consider the following
resources for background on the aggregation framework and its use:
- Documentation: :doc:`/core/aggregation`
- Reference: :doc:`/reference/aggregation`
- Examples: :doc:`/applications/aggregation`
TTL Collections
TTL collections remove expired data from a collection, using a special
index and a background thread that deletes expired documents every
minute. These collections are useful as an alternative to
:term:`capped collections <capped collection>` in some cases, such as for data
warehousing and caching cases, including: machine generated event data,
logs, and session information that needs to persist in a database
for only a limited period of time.
For more information, see the :doc:`/tutorial/expire-data` tutorial.
Concurrency Improvements
MongoDB 2.2 increases the server's capacity for concurrent
operations with the following improvements:
#. :issue:`DB Level Locking <SERVER-4328>`
#. :issue:`Improved Yielding on Page Faults <SERVER-3357>`
#. :issue:`Improved Page Fault Detection on Windows <SERVER-4538>`
To reflect these changes, MongoDB now provides changed and improved
reporting for concurrency and use, see :ref:`locks` and
:ref:`server-status-record-stats` in :doc:`server status
</reference/command/serverStatus>` and see
:doc:`mongotop </reference/program/mongotop>`, and :doc:`mongostat
.. todo:: add links to current op output documentation when it happens.
Improved Data Center Awareness with Tag Aware Sharding
MongoDB 2.2 adds additional support for geographic distribution or
other custom partitioning for sharded collections in :term:`clusters
<sharded cluster>`. By using this "tag aware" sharding, you can
automatically ensure that data in a sharded database system is always
on specific shards. For example, with tag aware sharding, you can
ensure that data is closest to the application servers that use that
data most frequently.
.. todo When draft/core/write-operations.txt goes live, change this below:
Shard tagging controls data location, and is complementary but
separate from replica set tagging, which controls :doc:`read
preference </core/read-preference>` and :ref:`write concern
<write-concern>`. For example, shard tagging can pin all
"USA" data to one or more logical shards, while replica set tagging
can control which :program:`mongod` instances (e.g. "``production``"
or "``reporting``") the application uses to service requests.
See the documentation for the following helpers in the :program:`mongo`
shell that support tagged sharding configuration:
- :method:`sh.addShardTag()`
- :method:`sh.addTagRange()`
- :method:`sh.removeShardTag()`
Also, see :doc:`/core/tag-aware-sharding` and
Fully Supported Read Preference Semantics
All MongoDB clients and drivers now support full :doc:`read
preferences </core/read-preference>`, including consistent
support for a full range of :ref:`read preference modes
<replica-set-read-preference-modes>` and :ref:`tag sets
<replica-set-read-preference-tag-sets>`. This support extends to the
:program:`mongos` and applies identically to single replica sets and
to the replica sets for each shard in a :term:`sharded cluster`.
Additional read preference support now exists in the :program:`mongo`
shell using the :method:`~cursor.readPref()` cursor method.
.. including tagging
Compatibility Changes
Authentication Changes
MongoDB 2.2 provides more reliable and robust support for
authentication clients, including drivers and :program:`mongos`
If your cluster runs with authentication:
- For all drivers, use the latest release of your driver and check
its release notes.
- In sharded environments,
to ensure that your cluster remains available during the upgrade
process you **must** use the :ref:`upgrade procedure for sharded clusters
.. _2.2-findandmodify-returns-null:
``findAndModify`` Returns Null Value for Upserts that Perform Inserts
In version 2.2, for :term:`upsert` that perform inserts with the
``new`` option set to ``false``, :dbcommand:`findAndModify` commands will
now return the following output:
.. code-block:: javascript
{ 'ok': 1.0, 'value': null }
In the :program:`mongo` shell, upsert :dbcommand:`findAndModify`
operations that perform inserts (with ``new`` set to ``false``.)only output a ``null`` value.
In version 2.0 these operations would return an empty document,
e.g. ``{ }``.
See: :issue:`SERVER-6226` for more information.
``mongodump`` 2.2 Output Incompatible with Pre-2.2 ``mongorestore``
If you use the :program:`mongodump` tool from the 2.2 distribution to
create a dump of a database, you must use a 2.2 (or later) version of
:program:`mongorestore` to restore that dump.
See: :issue:`SERVER-6961` for more information.
.. _2.2-ObjectId-toString-valueOf-methods:
``ObjectId().toString()`` Returns String Literal ``ObjectId("...")``
In version 2.2, the :method:`~ObjectId.toString()` method returns the
string representation of the :ref:`ObjectId() <core-object-id-class>`
object and has the format ``ObjectId("...")``.
Consider the following example that calls the
:method:`~ObjectId.toString()` method on the
``ObjectId("507c7f79bcf86cd7994f6c0e")`` object:
.. code-block:: javascript
The method now returns the *string*
Previously, in version 2.0, the method would return the *hexadecimal
string* ``507c7f79bcf86cd7994f6c0e``.
If compatibility between versions 2.0 and 2.2 is required, use
:ref:`ObjectId().str <core-object-id-class>`, which holds the
hexadecimal string value in both versions.
``ObjectId().valueOf()`` Returns hexadecimal string
In version 2.2, the :method:`~ObjectId.valueOf()` method returns the
value of the :ref:`ObjectId() <core-object-id-class>` object as a
lowercase hexadecimal string.
Consider the following example that calls the :method:`~ObjectId.valueOf()` method on the
``ObjectId("507c7f79bcf86cd7994f6c0e")`` object:
.. code-block:: javascript
The method now returns the *hexadecimal string*
Previously, in version 2.0, the method would return the *object*
If compatibility between versions 2.0 and 2.2 is required, use
:ref:`ObjectId().str <core-object-id-class>` attribute, which holds the
hexadecimal string value in both versions.
Behavioral Changes
.. _rn-2.2-collection-name-restriction:
Restrictions on Collection Names
In version 2.2, collection names cannot:
- contain the ``$``.
- be an empty string (i.e. ``""``).
This change does not affect collections created with now illegal names
in earlier versions of MongoDB.
These new restrictions are in addition to the existing restrictions on
collection names which are:
- A collection name should begin with a letter or an underscore.
- A collection name cannot contain the null character.
- Begin with the ``system.`` prefix. MongoDB
reserves ``system.``
for system collections, such as the
``system.indexes`` collection.
- The maximum size of a collection name is 128 characters, including
the name of the database. However, for maximum flexibility,
collections should have names less than 80 characters.
Collections names may have any other valid UTF-8 string.
See the :issue:`SERVER-4442` and the
:ref:`faq-restrictions-on-collection-names` FAQ item.
.. _rn-2.2-database-name-restriction-windows:
Restrictions on Database Names for Windows
Database names running on Windows can no longer contain the following
.. code-block:: none
/\. "*<>:|?
The names of the data files include the database name. If you attempt
to upgrade a database instance with one or more of these characters,
:program:`mongod` will refuse to start.
Change the name of these databases before upgrading. See
:issue:`SERVER-4584` and :issue:`SERVER-6729` for more information.
.. _2.2-id-indexes-capped-collections:
``_id`` Fields and Indexes on Capped Collections
All :term:`capped collections <capped collection>` now have an ``_id``
field by default, *if* they exist outside of the ``local`` database,
and now have indexes on the ``_id`` field. This change only affects capped
collections created with 2.2 instances and does not affect existing
capped collections.
See: :issue:`SERVER-5516` for more information.
New ``$elemMatch`` Projection Operator
The :projection:`$elemMatch` operator allows applications to narrow
the data returned from queries so that the query operation will only
return the first matching element in an array. See the
:doc:`/reference/operator/projection/elemMatch` documentation and the
:issue:`SERVER-2238` and :issue:`SERVER-828` issues for more
Windows Specific Changes
Windows XP is Not Supported
As of 2.2, MongoDB does not support Windows XP. Please upgrade to a
more recent version of Windows to use the latest releases of
MongoDB. See :issue:`SERVER-5648` for more information.
Service Support for ``mongos.exe``
You may now run :program:`mongos.exe` instances as a Windows
Service. See the :doc:`/reference/program/mongos.exe` reference and
:ref:`tutorial-mongod-as-windows-service` and :issue:`SERVER-1589` for
more information.
Log Rotate Command Support
MongoDB for Windows now supports log rotation by way of the
:dbcommand:`logRotate` database command. See :issue:`SERVER-2612` for
more information.
New Build Using SlimReadWrite Locks for Windows Concurrency
Labeled "2008+" on the `Downloads Page`_, this build for 64-bit
versions of Windows Server 2008 R2 and for Windows 7 or newer, offers
increased performance over the standard 64-bit Windows build of
MongoDB. See :issue:`SERVER-3844` for more information.
.. _`Downloads Page`:
Tool Improvements
Index Definitions Handled by ``mongodump`` and ``mongorestore``
When you specify the :option:`--collection <mongodump --collection>`
option to :program:`mongodump`, :program:`mongodump` will now backup
the definitions for all indexes that exist on the source
database. When you attempt to restore this backup with
:program:`mongorestore`, the target :program:`mongod` will rebuild all
indexes. See :issue:`SERVER-808` for more information.
:program:`mongorestore` now includes the :option:`--noIndexRestore
<mongorestore --noIndexRestore>` option to provide the preceding
behavior. Use :option:`--noIndexRestore <mongorestore --noIndexRestore>`
to prevent :program:`mongorestore` from building
previous indexes.
``mongooplog`` for Replaying Oplogs
The :program:`mongooplog` tool makes it possible to pull :term:`oplog`
entries from :program:`mongod` instance and apply them to another
:program:`mongod` instance. You can use :program:`mongooplog` to
achieve point-in-time backup of a MongoDB data set. See the
:issue:`SERVER-3873` case and the :doc:`/reference/program/mongooplog`
Authentication Support for ``mongotop`` and ``mongostat``
:program:`mongotop` and :program:`mongostat` now contain support for
username/password authentication. See :issue:`SERVER-3875` and
:issue:`SERVER-3871` for more information regarding this change. Also
consider the documentation of the following options for additional
- :option:`mongotop --username`
- :option:`mongotop --password`
- :option:`mongostat --username`
- :option:`mongostat --password`
Write Concern Support for ``mongoimport`` and ``mongorestore``
:program:`mongoimport` now provides an option to halt the import if
the operation encounters an error, such as a network interruption, a
duplicate key exception, or a write error.
The :option:`--stopOnError <mongoimport --stopOnError>` option
produce an error rather than silently continue importing data. See
:issue:`SERVER-3937` for more information.
In :program:`mongorestore`, the :option:`--w <mongorestore --w>`
option provides support for configurable write concern.
``mongodump`` Support for Reading from Secondaries
You can now run :program:`mongodump` when connected to a
:term:`secondary` member of a :term:`replica set`. See
:issue:`SERVER-3854` for more information.
``mongoimport`` Support for full 16MB Documents
Previously, :program:`mongoimport` would only import documents that
were less than 4 megabytes in size. This issue is now corrected, and
you may use :program:`mongoimport` to import documents that are at
least 16 megabytes ins size. See :issue:`SERVER-4593` for more
``Timestamp()`` Extended JSON format
MongoDB extended JSON now includes a new ``Timestamp()`` type to
represent the Timestamp type that MongoDB uses for timestamps in the
:term:`oplog` among other contexts.
This permits tools like :program:`mongooplog` and :program:`mongodump`
to query for specific timestamps. Consider the following
:program:`mongodump` operation:
.. code-block:: sh
mongodump --db local --collection --query '{"ts":{"$gt":{"$timestamp" : {"t": 1344969612000, "i": 1 }}}}' --out oplog-dump
See :issue:`SERVER-3483` for more information.
Shell Improvements
Improved Shell User Interface
2.2 includes a number of changes that improve the overall quality and
consistency of the user interface for the :program:`mongo` shell:
- Full Unicode support.
- Bash-like line editing features. See :issue:`SERVER-4312` for more
- Multi-line command support in shell history.
See :issue:`SERVER-3470` for more information.
- Windows support for the ``edit`` command. See :issue:`SERVER-3998` for
more information.
Helper to load Server-Side Functions
The :method:`db.loadServerScripts()` loads the contents of the current
database's ``system.js`` collection into the current :program:`mongo`
shell session. See :issue:`SERVER-1651` for more information.
Support for Bulk Inserts
If you pass an array of :term:`documents <document>` to the
:method:`~db.collection.insert()` method, the :program:`mongo`
shell will now perform a bulk insert operation. See
:issue:`SERVER-3819` and :issue:`SERVER-2395` for more information.
.. include:: /includes/note-bulk-inserts-on-sharded-clusters.rst
Support for Logging to Syslog
See the :issue:`SERVER-2957` case and the documentation of
the :setting:`syslog` run-time option or the :option:`mongod --syslog`
and :option:`mongos --syslog` command line-options.
``touch`` Command
Added the :dbcommand:`touch` command to read the data and/or indexes
from a collection into memory. See: :issue:`SERVER-2023` and
:dbcommand:`touch` for more information.
``indexCounters`` No Longer Report Sampled Data
:data:`indexCounters` now report actual counters that reflect index
use and state. In previous versions, these data were sampled. See
:issue:`SERVER-5784` and :data:`indexCounters` for more information.
Padding Specifiable on ``compact`` Command
See the documentation of the :dbcommand:`compact` and the
:issue:`SERVER-4018` issue for more information.
.. todo:: fix documentation and link
Added Build Flag to Use System Libraries
The Boost library, version 1.49, is now embedded in the MongoDB
code base.
If you want to build MongoDB binaries using system Boost libraries,
you can pass ``scons`` using the ``--use-system-boost`` flag, as follows:
.. code-block:: sh
scons --use-system-boost
When building MongoDB, you can also pass ``scons`` a flag to compile
MongoDB using only system libraries rather than the included versions
of the libraries. For example:
.. code-block:: sh
scons --use-system-all
See the :issue:`SERVER-3829` and :issue:`SERVER-5172` issues for more
Memory Allocator Changed to TCMalloc
To improve performance, MongoDB 2.2 uses the TCMalloc memory
allocator from Google Perftools. For more information about this
change see the :issue:`SERVER-188` and :issue:`SERVER-4683`. For more
information about TCMalloc, see the documentation of `TCMalloc`_ itself.
.. _`TCMalloc`:
Improved Logging for Replica Set Lag
When :term:`secondary` members of a replica set fall behind in
replication, :program:`mongod` now provides better reporting in the
log. This makes it possible to track replication in general and
identify what process may produce errors or halt replication. See
:issue:`SERVER-3575` for more information.
Replica Set Members can Sync from Specific Members
.. the following has been copied to source/administration/replica-sets.txt
The new :dbcommand:`replSetSyncFrom` command and new
:method:`rs.syncFrom()` helper in the :program:`mongo` shell make it
possible for you to manually configure from which member of the set a
replica will poll :term:`oplog` entries. Use these commands to
override the default selection logic if needed. Always exercise
caution with :dbcommand:`replSetSyncFrom` when overriding the default
Replica Set Members will not Sync from Members Without Indexes Unless ``buildIndexes: false``
.. the following has been copied to source/core/replication-internals.txt
To prevent inconsistency between members of replica sets, if the
member of a replica set has
:data:`~local.system.replset.members[n].buildIndexes` set to ``true``,
other members of the replica set will *not* sync from this member,
unless they also have
:data:`~local.system.replset.members[n].buildIndexes` set to
``true``. See :issue:`SERVER-4160` for more information.
New Option To Configure Index Pre-Fetching during Replication
.. the following has been copied to source/core/replication-internals.txt
By default, when replicating options, :term:`secondaries <secondary>`
will pre-fetch :ref:`indexes` associated with a query to improve replication
throughput in most cases. The :setting:`replIndexPrefetch` setting and
:option:`--replIndexPrefetch <mongod --replIndexPrefetch>` option allow administrators to disable
this feature or allow the :program:`mongod` to pre-fetch only the
index on the ``_id`` field. See :issue:`SERVER-6718` for more information.
Map Reduce Improvements
In 2.2 Map Reduce received the following improvements:
- :issue:`Improved support for sharded MapReduce <SERVER-4521>`, and
- :issue:`MapReduce will retry jobs following a config error <SERVER-4158>`.
Sharding Improvements
Index on Shard Keys Can Now Be a Compound Index
If your shard key uses the prefix of an existing index, then you do not
need to maintain a separate index for your shard key in addition to
your existing index. This index, however, cannot be a multi-key
index. See the :ref:`sharding-shard-key-indexes` documentation and
:issue:`SERVER-1506` for more information.
Migration Thresholds Modified
The :ref:`migration thresholds <sharding-migration-thresholds>` have
changed in 2.2 to permit more even distribution of :term:`chunks
<chunk>` in collections that have smaller quantities of data. See the
:ref:`sharding-migration-thresholds` documentation for more
.. Withholding from release notes. Internal feature.
Option to Disable ``splitVector`` for :program:`mongos` Instances
By default, all :program:`mongos` instances are responsible for
creating chunk splits. For deployments with large numbers of
:program:`mongos` instances, this may impact the performance of the
To ameliorate the additional load generated by these operations,
the new :program:`mongos` option :option:`--noAutoSplit <mongos>`
and the configuration file :setting:`noAutoSplit` setting both
disable chunk splitting for individual :program:`mongos` instances.
See :issue:`SERVER-6305` for more information.
Licensing Changes
Added License notice for Google Perftools (TCMalloc Utility). See the
`License Notice <>`_
and the :issue:`SERVER-4683` for more information.
- `MongoDB Downloads <>`_.
- `All JIRA issues resolved in 2.2 <>`_.
- `All backwards incompatible changes <>`_.
- `All third party license notices <>`_.
- `What's New in MongoDB 2.2 Online Conference <>`_.
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