Feature Category

Feature Details

DDS 4.0

DDS 4.2

Community edition MongoDB 4.2

Database Commands

The find command supports the allowDiskUse field, which allows MongoDB to use temporary files on disk to store data that exceeds the memory limit when processing non-indexed sort operations.

New syntax and usage of projection, such as
Currently, the projection supports aggregation syntax, for example, aggregation operators.
The projection supports mapping of specified fields in the JSON nested format.
In projection, the $character can be used to specify the subelement of the index of the mapped array element.

Distributed transaction

Supports distributed transaction functions. Distributed transactions are multi-document transactions on sharded clusters and replica sets. Starting with MongoDB 4.2, multi-document transactions. (whether on a sharded cluster or replica set) Also known as distributed transactions.

Remove the 16 MB limit for the total size of a transaction.

Drivers supporting version 4.2 must be used.

agglomerated

The aggregation capability is improved and data can be updated in the aggregation pipeline.
Add $merge.
Added $accumulator and $function.
Supports union All.
Add $unionWith.
For more aggregation operations, see #dds_01_0046/table583141110423.

Wildcard Index

Supports wildcard indexing.

Sharded cluster

Allows you to modify the shard key value of the cluster document.

Adjust the fields associated with the shard key.

A collection can be sharded using a composite shard key with a single hash field.

The length limit of the key is removed from 512 bytes.

Multi-document transactions allow the creation of indexes and collections (non-distributed transactions) to be performed.

Index

Remove the restriction on the length of the index field.

The length limit for index names is removed.

Composite indexes can contain hash indexes.

Supports the function of hiding indexes for commissioning.

Collection namespace limit.
The length of <database>.<collection> is increased from 120 bytes to 255 bytes.

Other Optimized Features

Default Read and Write Concern
Global default read/write concerns, involving connections and command read/write contexts.

Supports jumbo chunk migration.

Hedge query is supported.

Mongos supports the javascripts function to support.

Holds some special aggregation operators.