MongoDB 3.6 RC3 Release Highlights & Common Pitfalls Explained

Security

The default bind_ip changed to localhost in 3.6, which can cause startup delays if not adjusted. Resolve it by starting MongoDB with --bind_ip_all or adding net.bindIp: 0.0.0.0 or net.bindIpAll: true to the configuration file.

SSL enhancements : added opensslCipherConfig parameter.

Cursor restrictions : when authentication is enabled, developers can only issue getMore cursor requests.

Authentication restrictions : authenticationRestrictions added to db.createUser() and db.updateUser() to limit client IPs.

Custom role storage : convertToCapped method introduced.

Aggregation

The $lookup operator now supports let and pipeline for more powerful joins (see MongoDB documentation for syntax).

Additional aggregation operators introduced:

$listSessions

$listLocalSessions

$currentOp

$arrayToObject

$objectToArray

$mergeObjects

$dateFromString

$dateFromParts

$dateToParts

New db.aggregate() method allows admin‑level aggregation, e.g., using $currentOp or $listLocalSessions.

The REMOVE variable can delete a specified field within an aggregation pipeline (see documentation URL).

Array Update Operator Enhancements

The $[] positional all operator enables updating every element of an array in a single statement, supporting arithmetic operators like $divide and $sum.

Combined with $[<em>identifier</em>] and conditional expressions ( $cond), it allows targeted updates of array elements that meet specific criteria.

Mongo Shell Changes

New shell commands for session management have been added, including $listSessions and $listLocalSessions.

JSON Schema

The $jsonSchema operator lets you enforce collection validation rules. Use the required field to specify mandatory keys and the description field to annotate schema elements for better developer understanding.

Replica Sets

Online activation of authentication mode is now possible without restarting the replica set, eliminating downtime.

OpLog can be resized hot‑reloaded via the new replSetResizeOplog command, and protocol version 0 is being deprecated.

Sharded Clusters

A new parameter ShardingTaskExecutorPoolMaxConnecting controls the maximum number of concurrent connections for sharding tasks (see documentation URL).

Other Improvements

Each collection now receives a UUID.

Index names cannot contain the asterisk (*) character.

Multi‑key indexes now support documents without array fields. listDatabases command gains nameOnly and filter options.

Network traffic now supports zlib compression.

The author plans future posts on enabling replica set authentication online and deeper exploration of the $jsonSchema feature.