• Resolved issue in WiredTiger’s capped collections implementation that caused a server crash: SERVER- 17345$^{224}$. 

• Fixed issue is initial sync with duplicate _id entries: SERVER-17487$^{225}$. 

• Fixed deadlock condition in MMAPv1 between the journal lock and the oplog collection lock: SERVER- 17416$^{226}$. 

• All issues closed in 3.0.1 227 

## 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 228 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$^{229}$, 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 Mon- goDB features, including operations that report on server, database, and collection statistics. Switching to WiredTiger, however, requires a change to the on-disk storage format (page 804). For instructions on changing the storage engine to WiredTiger, see the appropriate sections in the Upgrade MongoDB to 3.0 (page 810) documentation. 

MongoDB 3.0 replica sets and sharded clusters can have members with different storage engines; however, perfor- mance can vary according to workload. For details, see the appropriate sections in the Upgrade MongoDB to 3.0 (page 810) documentation. 

The WiredTiger storage engine requires the latest official MongoDB drivers. For more information, see WiredTiger and Driver Version Compatibility (page 804). 

## See also: 

Support for touch Command (page 805), WiredTiger Storage Engine (page 90) section in the Storage (page 89) docu- mentation 

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 (page 90) section in the Storage (page 89) documentation 

