Release Notes for MongoDB 2.6

Release Notes for MongoDB 2.6

April 8, 2014

MongoDB 2.6 is now available. Key features include aggregation enhancements, text search integration, query engine improvements, a new write operation protocol, and security enhancements.

MMS 1.4, which includes On-Prem Backup in addition to Monitoring, is now also available. See MMS 1.4 documentation and the MMS 1.4 release notes for more information.

Major Changes

The following changes in MongoDB affect both the standard and Enterprise editions:

Aggregation Enhancements

The aggregation pipeline adds the ability to return result sets of any size either by returning a cursor, or optionally writing the output to a collection. Additionally, the aggregation pipeline supports variables and adds new operations to handle sets and redact data.

- The db.collection.aggregate() now returns a cursor, which enables the aggregation pipeline to return result sets of any size.

- Aggregation pipelines now support an explain operation to aid analysis of aggregation operations.

- Aggregation can now use a more efficient external-disk-based sorting process.

- New pipeline stages:

- $out stage to output to a collection

- $redact stage to allow additional control to accessing the data

- New or modified operators:

- set expression operators

- $let and $map operators to allow for the use of variables

- $literal operator and $size operator

- $cond expression now accepts either an object or an array

Text Search Integration

Text search is now enabled by default, and the query system, including the aggregation pipeline $matchstage, includes the $text operator which resolves text-search queries.

MongoDB 2.6 includes an updated text index format and deprecates the text command.

Insert and Update Improvements

Improvements to the update and insert systems include additional operations and improvements that increase consistency of modified data.

- MongoDB preserves the order of the document fields following write operations except for the following cases:

- The _id field is always the first field in the document.

- Updates that include renaming of field names may result in the reordering of fields in the document.

- New or enhanced update operators:

- $bit operator supports bitwise xor operation.

- $min and $max operators that perform conditional update depending on the relative size of the specified value and the current value of a field.

- $push operator has enhanced support for the $sort$slice, and $each modifiers and supports a new $position modifier.

- $currentDate operator to set the value of a field to the current date.

- The $mul operator for multiplicative increments for insert and update operations.


Updates Enforce Field Name Restrictions

New Write Operation Protocol

A new protocol for write operations integrates write operations with write concerns. The write protocol also provides improved support for bulk operations.

2.6 adds write commands, insertupdate, and delete, which provide the basis for these improvements and affect the behavior of the mongo shell. All officially supported MongoDB drivers support the new write commands.

As part of these changes, the mongo shell now includes methods to perform bulk write operations. SeeBulk() for more information.


Write Method Acknowledgements

MSI Package for MongoDB Available for Windows

MongoDB now distributes MSI packages for Microsoft Windows. This is the recommended method for MongoDB installation under Windows.

Security Improvements

MongoDB 2.6 enhances support for secure deployments by improved SSL support, x.509-based authentication, an improved authorization system with more granular controls, as well as centralized credential storage and improved user management tools.

Specifically these changes include:

- New authorization model which provides the ability to create custom User-Defined Roles and the ability to specify user privileges at a collection-level granularity.

- A global user management, storing all user and user-defined role data in the admin database and providing a new set of commands for managing users and roles.

- x.509 certificate authentication, for client authentication as well as for internal authentication of sharded and/or replica set cluster members. x.509 authentication is only available for deployments using SSL.

- Enhanced SSL Support:

- Support rolling upgrades of clusters to use SSL.

- MongoDB Tools support connections to mongod and mongos instances using SSL connection.

- Can prompt for passphrase by mongod or mongos at startup.

- Require the use of strong SSL ciphers, with a minimum 128-bit key length for all connections. The strong-cipher requirement prevents an old or malicious client from forcing use of a weak cipher.

- MongoDB disables the http interface by default, limiting network exposure. To enable the interface, see httpinterface.


New Authorization ModelSSL Certificate Hostname Validation, and Security Checklist.

Query Engine Improvements

- MongoDB can now use index intersection to fulfill queries supported by more than one index.

- Index Filters to limit which indexes can become the winning plan for a query.

- Query Plan Cache Methods methods to view and clear the query plans cached by the query optimizer.

- MongoDB can now use count() with hint(). See count() for details.


Geospatial Enhancements

- Introduce version 2 of 2dsphere indexes.

- Support for MultiPointMultiLineStringMultiPolygon, and GeometryCollection.

- Support for geospatial query clauses in $or expressions.


2dsphere Index Version 2$maxDistance ChangesDeprecated $uniqueDocsStronger Validation of Geospatial Queries,

Index Build Enhancements

- Background index build allowed on secondaries; i.e. if you initiate a background index build on a primary, the secondaries will replicate the index build in the background.

- Automatic rebuild of interrupted index builds after a restart.

- If a standalone or a primary instance terminates during an index build without a clean shutdown,mongod now restarts the index build when the instance restarts. If the instance shut down cleanly or if a user killed the index build, the interrupted index builds do not automatically restart upon the restart of the server.

- If a secondary instance terminates during an index build, the mongod instance will now restart the interrupted index build when the instance restarts.

To disable this behavior, use the --noIndexBuildRetry command line option.

- ensureIndex() now wraps a new createIndex command.

- The dropDups option to ensureIndex() and createIndex is deprecated.


Enforce Index Key Length Limit

Enhanced Sharding and Replication Administration

- New cleanupOrphaned command to remove orphaned documents from a shard.

- New mergeChunks command to combine contiguous chunks located on a single shard. SeemergeChunks and Merge Chunks in a Sharded Cluster.

- New rs.printReplicationInfo() and rs.printSlaveReplicationInfo() methods to provide a formatted report of the status of a replica set from the perspective of the primary and the secondary, respectively.

Operational Changes


usePowerOf2Sizes is the default allocation strategy for all new collections. The new allocation strategy uses more storage relative to total document size, but results in lower levels of storage fragmentation and more predictable storage capacity planning over time.

To use the previous exact fit allocation strategy:

- For a specific collection, use collMod with usePowerOf2Sizes set to false.

- For all new collections on an entire mongod instance, set newCollectionsUsePowerOf2Sizesto false.

See Storage for more information about MongoDB’s storage system.


- Removed upward limit for the maxIncomingConnections for mongod and mongos. Previous versions capped the maximum possible maxIncomingConnections setting at 20,000 connections.

- Connection pools for mongos instance may be used by multiple MongoDB servers. This can reduce the number of connections needed for high volume workloads and reduce resource consumption in sharded clusters.

- The C++ driver now monitors replica set health with the isMaster command instead ofreplSetGetStatus. This allows the C++ driver to support systems that require authentication.

- New cursor.maxTimeMS() and corresponding maxTimeMS option for commands to specify a time limit.

Tool Improvements

- mongo shell supports a global /etc/mongorc.js.

- All MongoDB executable files now support the --quiet option to suppress all logging output except for error messages.

- mongoimport uses the input filename, without the file extension if any, as the collection name if run without the -c or --collection specification.

- mongoexport can now constrain export data using --skip and --limit as well as order the documents in an export using the --sort option.

- mongostat can support the use of --rowcount (-n) with the --discover option to produce the specified number of output lines.

- Add strict mode representation for data_numberlong for use by mongoexport and mongoimport.

MongoDB Enterprise Features

The following changes are specific to MongoDB Enterprise Editions:

MongoDB Enterprise for Windows

MongoDB Enterprise for Windows is now available. It includes support for Kerberos, SSL, and SNMP.

MongoDB Enterprise for Windows does not include LDAP support for authentication.

MongoDB Enterprise for Windows includes with OpenSSL version 1.0.1g.


MongoDB Enterprise adds auditing capability for mongod and mongos instances. See Auditing for details.

LDAP Support for Authentication

MongoDB Enterprise provides support for proxy authentication of users. This allows administrators to configure a MongoDB cluster to authenticate users by proxying authentication requests to a specified Lightweight Directory Access Protocol (LDAP) service. See Authenticate Using SASL and LDAP for details.

MongoDB Enterprise for Windows does not include LDAP support for authentication.

MongoDB does not support LDAP authentication in mixed sharded cluster deployments that contain both version 2.4 and version 2.6 shards. See Upgrade MongoDB to 2.6 for upgrade instructions.

Expanded SNMP Support

MongoDB Enterprise has greatly expanded its SNMP support to provide SNMP access to nearly the full range of metrics provided by db.serverStatus().


SNMP Changes

Additional Information

Changes Affecting Compatibility

Some changes in 2.6 can affect compatibility and may require user actions. The 2.6 mongo shell provides andb.upgradeCheckAllDBs() method to perform a check for upgrade preparedness for some of these changes.

See Compatibility Changes in MongoDB 2.6 for a detailed list of compatibility changes.


All Backwards incompatible changes (JIRA).

Upgrade Process

See Upgrade MongoDB to 2.6 for full upgrade instructions.


To download MongoDB 2.6, go to the downloads page.

Other Resources

- All JIRA issues resolved in 2.6.

- All Third Party License Notices.