MongoDB Documentation, Release 3.0.4 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. WiredTiger (page 198) section in the Production Notes (page 197) 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 (page 804). MMAPv1 Record Allocation Behavior Changes MongoDB 3.0 no longer implements dynamic record alloca- tion and deprecates paddingFactor . The default allocation strategy for collections in instances that use MMAPv1 is power of 2 allocation (page 91), 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 (page 91). 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. Dynamic Record Allocation (page 805) In MongoDB 3.0, replica sets can have up to 50 members. 230 The following drivers support the larger replica sets: 800 Chapter 12. Release Notes 230 The maximum number of voting members remains at 7. • C# (.NET) Driver 1.10 • Java Driver 2.13 • Python Driver (PyMongo) 3.0 • Ruby Driver 2.0 • Node.JS Driver 2.0 See also: Replica Sets Increased Number of Replica Set Members MMAPv1 Improvements See also: