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Release Notes for MongoDB 3.0

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March 3, 2015

MongoDB 3.0 is now available. Key features include support for the WiredTiger storage engine, pluggable storage engine API, SCRAM-SHA-1 authentication mechanism, and improved explain functionality.

MongoDB Ops Manager, which includes Automation, Backup, and Monitoring, is now also available. See the Ops Manager documentation and the Ops Manager release notes for more information.

Minor Releases

3.0.9 – Jan 26, 2016

  • Fixed issue where queries which specify sort and batch size can return results out of order if documents are concurrently updated. SERVER-19996
  • Fixed performance issue where large amounts of create and drop collections can cause listDatabases to be slow under WiredTiger. SERVER-20961
  • Modified the authentication failure message to include the client IP address. SERVER-22054
  • All issues closed in 3.0.9

3.0.8 – Dec 15, 2015

3.0.7 – Oct 13, 2015

3.0.6 – August 24, 2015

3.0.5 – July 28, 2015

3.0.4 – June 16, 2015

  • Fix missed writes with concurrent inserts during chunk migration from shards with WiredTiger primaries: SERVER-18822
  • Resolve write conflicts with multi-update updates with upsert=true with the Wired Tiger Storage engine: SERVER-18213
  • Fix case where secondary reads could block replication: SERVER-18190
  • Improve performance on Windows with WiredTiger and documents larger than 16kb: SERVER-18079
  • Fix issue where WiredTiger data files are not correctly recovered following unexpected system restarts: SERVER-18316
  • All issues closed in 3.0.4

3.0.3 – May 12, 2015

3.0.2 – April 9, 2015

3.0.1 – March 17, 2015

  • Fixed race condition in WiredTiger between inserts and checkpoints that could result in lost records: SERVER-17506.
  • Resolved issue in WiredTiger’s capped collections implementation that caused a server crash: SERVER-17345.
  • Fixed issue is initial sync with duplicate _id entries: SERVER-17487.
  • Fixed deadlock condition in MMAPv1 between the journal lock and the oplog collection lock: SERVER-17416.
  • All issues closed in 3.0.1

Major Changes

Pluggable Storage Engine API

MongoDB 3.0 introduces a pluggable storage engine API that allows third parties to develop storage engines for MongoDB.

WiredTiger

MongoDB 3.0 introduces support for the WiredTiger storage engine. With the support for WiredTiger, MongoDB now supports two storage engines:

  • MMAPv1, the storage engine available in previous versions of MongoDB and the default storage engine for MongoDB 3.0, and
  • WiredTiger, available only in the 64-bit versions of MongoDB 3.0.

WiredTiger Usage

WiredTiger is an alternate to the default MMAPv1 storage engine. WiredTiger supports all MongoDB features, including operations that report on server, database, and collection statistics. Switching to WiredTiger, however, requires a change to the on-disk storage format. For instructions on changing the storage engine to WiredTiger, see the appropriate sections in the Upgrade MongoDB to 3.0 documentation.

MongoDB 3.0 replica sets and sharded clusters can have members with different storage engines; however, performance can vary according to workload. For details, see the appropriate sections in the Upgrade MongoDB to 3.0 documentation.

The WiredTiger storage engine requires the latest official MongoDB drivers. For more information, see WiredTiger and Driver Version Compatibility.

See also

Support for touch Command, WiredTiger Storage Engine documentation

WiredTiger Configuration

To configure the behavior and properties of the WiredTiger storage engine, see storage.wiredTiger configuration options. You can set WiredTiger options on the command line.

See also

WiredTiger Storage Engine

WiredTiger Concurrency and Compression

The 3.0 WiredTiger storage engine provides document-level locking and compression.

By default, WiredTiger compresses collection data using the snappy compression library. WiredTiger uses prefix compression on all indexes by default.

See also

WiredTiger section in the Production Notes, the blog post New Compression Options in MongoDB 3.0

MMAPv1 Improvements

MMAPv1 Concurrency Improvement

In version 3.0, the MMAPv1 storage engine adds support for collection-level locking.

MMAPv1 Configuration Changes

To support multiple storage engines, some configuration settings for MMAPv1 have changed. See Configuration File Options Changes.

MMAPv1 Record Allocation Behavior Changes

MongoDB 3.0 no longer implements dynamic record allocation and deprecates paddingFactor. The default allocation strategy for collections in instances that use MMAPv1 is power of 2 allocation, which has been improved to better handle large document sizes. In 3.0, the usePowerOf2Sizes flag is ignored, so the power of 2 strategy is used for all collections that do not have noPadding flag set.

For collections with workloads that consist only of inserts or in-place updates (such as incrementing counters), you can disable the power of 2 strategy. To disable the power of 2 strategy for a collection, use the collMod command with the noPadding flag or the db.createCollection() method with the noPadding option.

Warning

Do not set noPadding if the workload includes removes or any updates that may cause documents to grow. For more information, see No Padding Allocation Strategy.

When low on disk space, MongoDB 3.0 no longer errors on all writes but only when the required disk allocation fails. As such, MongoDB now allows in-place updates and removes when low on disk space.

See also

Dynamic Record Allocation

Replica Sets

Increased Number of Replica Set Members

In MongoDB 3.0, replica sets can have up to 50 members. [1] The following drivers support the larger replica sets:

  • C# (.NET) Driver 1.10
  • Java Driver 2.13
  • Python Driver (PyMongo) 3.0
  • Ruby Driver 2.0
  • Node.JS Driver 2.0

The C, C++, Perl, and PHP drivers, as well as the earlier versions of the Ruby, Python, and Node.JS drivers, discover and monitor replica set members serially, and thus are not suitable for use with large replica sets.

[1]The maximum number of voting members remains at 7.

Replica Set Step Down Behavior Changes

The process that a primary member of a replica set uses to step down has the following changes:

  • Before stepping down, replSetStepDown will attempt to terminate long running user operations that would block the primary from stepping down, such as an index build, a write operation or a map-reduce job.
  • To help prevent rollbacks, the replSetStepDown will wait for an electable secondary to catch up to the state of the primary before stepping down. Previously, a primary would wait for a secondary to catch up to within 10 seconds of the primary (i.e. a secondary with a replication lag of 10 seconds or less) before stepping down.
  • replSetStepDown now allows users to specify a secondaryCatchUpPeriodSecs parameter to specify how long the primary should wait for a secondary to catch up before stepping down.

Other Replica Set Operational Changes

  • Initial sync builds indexes more efficiently for each collection and applies oplog entries in batches using threads.
  • Definition of w: “majority” write concern changed to mean majority of voting nodes.
  • Stronger restrictions on Replica Set Configuration. For details, see Replica Set Configuration Validation.
  • For pre-existing collections on secondary members, MongoDB 3.0 no longer automatically builds missing _id indexes.

See also

Replication Changes in Compatibility Changes in MongoDB 3.0

Sharded Clusters

MongoDB 3.0 provides the following enhancements to sharded clusters:

  • Adds a new sh.removeTagRange() helper to improve management of sharded collections with tags. The new sh.removeTagRange() method acts as a complement to sh.addTagRange().
  • Provides a more predictable read preference behavior. mongos instances no longer pin connections to members of replica sets when performing read operations. Instead, mongos reevaluates read preferences for every operation to provide a more predictable read preference behavior when read preferences change.
  • Provides a new writeConcern setting to configure the write concern of chunk migration operations. You can configure the writeConcern setting for the balancer as well as for moveChunk and cleanupOrphaned commands.
  • Improves visibility of balancer operations. sh.status() includes information about the state of the balancer. See sh.status() for details.

See also

Sharded Cluster Setting in Compatibility Changes in MongoDB 3.0

Security Improvements

MongoDB 3.0 includes the following security enhancements:

  • MongoDB 3.0 adds a new SCRAM-SHA-1 challenge-response user authentication mechanism. SCRAM-SHA-1 requires a driver upgrade if your current driver version does not support SCRAM-SHA-1. For the driver versions that support SCRAM-SHA-1, see Upgrade Drivers.
  • Increases restrictions when using the Localhost Exception to access MongoDB. For details, see Localhost Exception Changed.

See also

Security Changes

Improvements

New Query Introspection System

MongoDB 3.0 includes a new query introspection system that provides an improved output format and a finer-grained introspection into both query plan and query execution.

For details, see the new db.collection.explain() method and the new explain command as well as the updated cursor.explain() method.

For information on the format of the new output, see Explain Results.

Enhanced Logging

To improve usability of the log messages for diagnosis, MongoDB categorizes some log messages under specific components, or operations, and provides the ability to set the verbosity level for these components. For information, see Log Messages.

MongoDB Tools Enhancements

All MongoDB tools except for mongosniff and mongoperf are now written in Go and maintained as a separate project.

  • New options for parallelized mongodump and mongorestore. You can control the number of collections that mongorestore will restore at a time with the --numParallelCollections option.
  • New options -excludeCollection and --excludeCollectionsWithPrefix for mongodump to exclude collections.
  • mongorestore can now accept BSON data input from standard input in addition to reading BSON data from file.
  • mongostat and mongotop can now return output in JSON format with the --json option.
  • Added configurable write concern to mongoimport, mongorestore, and mongofiles. Use the --writeConcern option. The default writeConcern has been changed to ‘w:majority’.
  • mongofiles now allows you to configure the GridFS prefix with the --prefix option so that you can use custom namespaces and store multiple GridFS namespaces in a single database.

See also

MongoDB Tools Changes

Indexes

  • Background index builds will no longer automatically interrupt if dropDatabase, drop, dropIndexes operations occur for the database or collection affected by the index builds. The dropDatabase, drop, and dropIndexes commands will still fail with the error message a background operation is currently running, as in 2.6.
  • If you specify multiple indexes to the createIndexes command,
    • the command only scans the collection once, and
    • if at least one index is to be built in the foreground, the operation will build all the specified indexes in the foreground.
  • For sharded collections, indexes can now cover queries that execute against the mongos if the index includes the shard key.

See also

Indexes in Compatibility Changes in MongoDB 3.0

Query Enhancements

MongoDB 3.0 includes the following query enhancements:

  • For geospatial queries, adds support for “big” polygons for $geoIntersects and $geoWithin queries. “Big” polygons are single-ringed GeoJSON polygons with areas greater than that of a single hemisphere. See $geometry, $geoIntersects, and $geoWithin for details.
  • For aggregate(), adds a new $dateToString operator to facilitate converting a date to a formatted string.
  • Adds the $eq query operator to query for equality conditions.

See also

2d Indexes and Geospatial Near Queries

Distributions and Supported Versions

Most non-Enterprise MongoDB distributions now include support for TLS/SSL. Previously, only MongoDB Enterprise distributions came with TLS/SSL support included; for non-Enterprise distributions, you had to build MongoDB locally with the --ssl flag (i.e. scons --ssl).

32-bit MongoDB builds are available for testing, but are not for production use. 32-bit MongoDB builds do not include the WiredTiger storage engine.

MongoDB builds for Solaris do not support the WiredTiger storage engine.

MongoDB builds are available for Windows Server 2003 and Windows Vista (as “64-bit Legacy”), but the minimum officially supported Windows version is Windows Server 2008.

See also

Platform Support, Deprecation of 32-bit Versions

Package Repositories

Non-Enterprise MongoDB Linux packages for 3.0 and later are in a new repository. Follow the appropriate Linux installation instructions to install the 3.0 packages from the new location.

MongoDB Enterprise Features

Auditing

Auditing in MongoDB Enterprise can filter on any field in the audit message, including the fields returned in the param document. This enhancement, along with the auditAuthorizationSuccess parameter, enables auditing to filter on CRUD operations. However, enabling auditAuthorizationSuccess to audit of all authorization successes degrades performance more than auditing only the authorization failures.

Additional Information

Changes Affecting Compatibility

Some changes in 3.0 can affect compatibility and may require user actions. For a detailed list of compatibility changes, see Compatibility Changes in MongoDB 3.0.

Upgrade Process

See Upgrade MongoDB to 3.0 for full upgrade instructions.

Download

To download MongoDB 3.0, go to the downloads page.

See also

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