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Release Notes for MongoDB 3.0

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  • Minor Releases
  • Major Changes
  • Replica Sets
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  • Security Improvements
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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.

Issues fixed:

  • SERVER-27164: Deadlock during initial sync or steady state replication when CRUD operations implicitly create collections on the same database.
  • SERVER-28548: In MMAPv1, index readers/writers can return invalid data if record no longer exists.
  • All issues closed in 3.0.15

Issues fixed:

  • Incorrect memory access on 3.0.13 triggers segmentation fault: SERVER-26889

Issues fixed:

Issues fixed:

Issues fixed:

  • For MongoDB 3.0.9 and MongoDB 3.0.10, during chunk migration, insert and update operations to documents in the migrating chunk are not reflected in the destination shard: SERVER-23425

Issues fixed:

Issues fixed:

  • Queries which specify sort and batch size can return results out of order if documents are concurrently updated. SERVER-19996
  • Large amounts of create and drop collections can cause listDatabases to be slow under WiredTiger. SERVER-20961
  • Authentication failure message includes server IP address instead of the client IP address. SERVER-22054
  • All issues closed in 3.0.9

Issues fixed:

Issues fixed:

Issues fixed:

Issues fixed and improvements:

Issues fixed:

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

Issues fixed:

Issues fixed:

Issues fixed:

  • Race condition in WiredTiger between inserts and checkpoints that could result in lost records: SERVER-17506.
  • WiredTiger's capped collections implementation causes a server crash: SERVER-17345.
  • Initial sync with duplicate _id entries: SERVER-17487.
  • Deadlock condition in MMAPv1 between the journal lock and the oplog collection lock: SERVER-17416.
  • All issues closed in 3.0.1

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

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 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.

Tip
See also:

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.

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.

Tip

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

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

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 legacy 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.

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.
  • 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.

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.

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 Requirements.
  • Increases restrictions when using the Localhost Exception to access MongoDB. For details, see Localhost Exception Changed.
Tip

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.

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.

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.
  • 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.

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.

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.

Tip

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.

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.

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.

See Upgrade MongoDB to 3.0 for full upgrade instructions.

To download MongoDB 3.0, go to the downloads page.

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