Compatibility Changes in MongoDB 6.1

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Aggregation

Removed Options
Time Series Collections
Server Parameters
No Automatic Chunk Splitting
Sharding Metrics Changes

Important

MongoDB 6.1 is a rapid release and is only supported for MongoDB Atlas. MongoDB 6.1 is not supported for use on-premises. For more information, see MongoDB Versioning.

To install the latest MongoDB version supported for on-premises use, MongoDB 6.0, see the MongoDB 6.0 installation instructions.

This page describes changes introduced in MongoDB 6.1 that can affect compatibility with older versions of MongoDB.

Aggregation

The following changes to aggregation can affect compatibility with older versions of MongoDB.

`$add` Floating Point Rounding Errors

Starting in MongoDB 6.1, when an $add expression receives an input list with multiple floating point values, MongoDB may return slightly different results compared to previous versions.

The $add expression no longer accounts for floating-point rounding errors. As a result, $add behaves like addition in most programming languages.

For example, the following $add expression returns a different result when run on MongoDB 6.1 compared to older versions:

db.test.aggregate(
   [
     {
        $project: {
           sumOfValues: {
              $add: [ 0.1, 0.2, 0.3 ]
           }
         }
      }
   ]
)

MongoDB 6.1 and later output:

[
  {
    _id: ObjectId("6390f8085425651d8d0ef0a7"),
    sumOfValues: 0.6000000000000001
  }
]

MongoDB 6.0 and earlier output:

[
  {
    _id: ObjectId("6390f8085425651d8d0ef0a7"),
    sumOfValues: 0.6
  }
]

Removed Options

Starting in MongoDB 6.1, journaling is always enabled. As a result, MongoDB removes the storage.journal.enabled option and the corresponding --journal and --nojournal command-line options.

Time Series Collections

Views Not Permitted on Bucket Collection Namespace

You cannot create a view from a time series bucket collection namespace (namely, a collection prefixed with system.buckets).

If you are upgrading to MongoDB 6.1 from a prior version, you must drop all views which are created on system.buckets collections.

Server Parameters

Starting in MongoDB 6.1, the default value for coordinateCommitReturnImmediatelyAfterPersistingDecision is false.

No Automatic Chunk Splitting

Starting in MongoDB 6.1, automatic chunk splitting is not performed. This is because of balancing policy improvements. Auto-splitting commands still exist, but do not perform an operation. For details, see Balancing Policy Changes.

Starting in MongoDB 6.1, the following auto-splitting commands do not perform an operation:

Sharding Metrics Changes

currentOp.opStatus is removed from the resharding metrics in MongoDB 6.1. For a list of new metrics that replace the reporting currentOp.opStatus provided, see the release notes.

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Release Notes for MongoDB 6.1

6.1 Changelog