MongoDB 4.0 New Features ~ Atikh's DBA blog

MongoDB 4.0 has been released on Aug 6, 2018, with tremendous new features specially ACID transactions.

I have listed the MongoDB 4.0 new features below

Read concern snapshot

MongoDB 4.0 introduces a new concern level snapshot for the multi-document transactions.
Read concern helps in targeting consistency and isolation properties of data
This new feature ensures that a consistent view of data is returned to the client, whether data is being modified simultaneously

Data Type Conversions

This is new in MongoDB 4.0 to convert data types, this comes under the aggregation framework and can be used with the help of the $convert expression

New String Operators

Below are the string operators added in the new version 4.0

$ltrim : Removes white spaces or specified characters from beginning of string
$rtrim : Removes white spaces or specified characters from end of the string
$trim : Removes white spaces or specified characters from beginning and end of the string

Read Preference

In the previous release MongoDB blocked secondary reads while oplog entries were applied.
Now there is improved read latency and increased throughput from the replica set which helps in maintaining a consistent ordering of data

Sharding Operations and Migration throughput

Sharded migrations are now up 40% faster helping for better distribution of data
Operations can list and kill queries running in shared cluster.

Locking System

By default, multi-document transactions wait 5 milliseconds to acquire locks required by operations in transactions
If transactions can not acquire their required locks within 5 milliseconds the transactions abort

The latest Minor release is 4.0.5 (Dec 20, 2018)

Below will be featured in the upcoming MongoDB 4.2

MongoDB 4.0 New Features