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This article introduces whether MongoDB 3.0 supports multiple storage engines, the content is very detailed, interested friends can use for reference, I hope it can be helpful to you.

MongoDB 3.0 has been officially released, with updates mainly related to storage engine, backup set, sharding cluster, and security.

The default storage engine for MongoDB 3.0is still MMAPv1, but in addition to adding set-level locks to improve concurrency and changing partial settings to support multiple storage engines, it also changes record allocation behavior. This version no longer uses the dynamic record allocation policy and deprecates the paddingFactor identity and uses the power allocation policy of 2 instead. Therefore, in version 3.0, the usePowerOf2Sizes identity is ignored and all collections will use this policy without setting the noPadding identity. However, if the workload of the collection contains only inserts or in-place updates, you should disable this policy.

In addition to improving the default storage engine, MongoDB 3.0 introduces a pluggable storage engine, API, which allows third parties to develop a storage engine for MongoDB. In addition, this version also supports the WiredTiger storage engine, but only for the 64-bit version of MongoDB 3.0. As an alternative to MMAPv1, WiredTiger supports all the features of MongoDB. It is important to note that switching to WiredTiger requires changing the disk storage format. For the storage engine switching instructions, please see the MongoDB 3.0 upgrade documentation. In addition, WiredTiger also requires the latest version of the official MongoDB driver, for driver version compatibility information, please see here.

MongoDB 3.0 increases the number of backup set members to 50, although the maximum number of voting members is 7. Currently, only the following drivers support large backup sets:

C # (.NET) Driver 1.10

Java Driver 2.13

Python Driver (PyMongo) 3.0 +

Ruby Driver 2.0 +

Node.JS Driver 2.0 +

PyMongo 3.0, Ruby Driver 2.0, and Node.JS Driver 2.0 are under development. In addition, the demotion behavior of the backup set Master member (primary member) has also changed.

In terms of sharding clustering, MongoDB 3.0 makes the following enhancements:

Add sh.removeTagRange () as a supplement to sh.addTagRange ()

Provides a more predictable "read preference (read preference)" in which the mongos instance no longer fixes the connection to the members of the backup set when performing a read operation, but reevaluates the read preference each time the operation is performed

A new writeConcern setting is provided to configure write concern (write concern) for block migration operations, as well as for balancer, moveChunk, and cleanupOrphaned commands

To improve the visibility of the balancer operation, sh.status () contains the status information of the balancer.

In terms of security, MongoDB 3.0 adds a new user authentication mechanism, SCRAM-SHA-1, and adds restrictions on using the Localhost Exception mechanism to access MongoDB (see here for more details).

Other improvements include: adding a new query introspection system to improve the query output format; classifying some log messages under specific components or operations to improve log availability, and can set the information display level for the component; rewriting all MongoDB tools in the go language, and each tool is maintained as a separate project; improved indexing and enhanced queries.

Along with MongoDB 3.0, MongoDB Ops Manager has also been officially released.

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