Release Notes for MongoDB 8.3

serverStatus Output

serverStatus includes the following new fields in its output:

• aggregate.withExtension sub-field in metrics.commands.aggregate, tracking success and failure counts

• shardingStatistics.databaseCriticalSectionStatistics

• shardingStatistics.collectionCriticalSectionStatistics

• shardingStatistics.databaseVersionUpdateCounters

• metrics.ttl.deletedKeys

• metrics.ttl.durationMicros

• metrics.ttl.examinedDocuments

• metrics.ttl.examinedKeys

• metrics.extension

• metrics.extension.totalAggStageExecMicros

• metrics.extension.apiCallSuccesses

• metrics.extension.apiCallFailures

• metrics.extension.vectorSearch

• metrics.extension.vectorSearch.legacyVectorSearchUsed

• metrics.extension.vectorSearch.extensionVectorSearchUsed

• metrics.extension.vectorSearch.onViewKickbackRetries

• metrics.extension.vectorSearch.inSubpipelineKickbackRetries

MongoDB 8.3 removes the service field in the serverStatus output.

Starting in MongoDB 8.3, you can exclude all optional fields from the serverStatus output by specifying none: 1. After you exclude all optional fields, you can then specify the fields you want to include.

For details, see Exclude All Optional Fields.

You can also optionally specify lockContentionMetrics: 1 in the serverStatus command to include lockContentionMetrics in the output.

String Conversion Enhancements

Starting in MongoDB 8.3, $toString can convert additional BSON types to strings, including objects, arrays, regular expressions, MaxKeys, MinKeys, and timestamps. For details, see $toString.

Geospatial Index Generation

Starting in MongoDB 8.3, if a document contains both GeoJSON and legacy numeric coordinate fields, geospatial index generation prioritizes GeoJSON coordinates.

If your documents contain legacy numeric coordinate values that precede GeoJSON coordinates and existing indexes rely on that behavior, you might need to rebuild your geospatial indexes.

This change may require you to rebuild geospatial indexes if your documents contain legacy numeric coordinate values that precede GeoJSON coordinates and existing indexes rely on that behavior. Review geospatial queries to confirm they return expected results.

cachePressureQueryPeriodMilliseconds Parameter

MongoDB 8.3 adds the cachePressureQueryPeriodMilliseconds parameter which sets the time interval MongoDB waits between checks for storage engine cache pressure. If the storage engine is under cache pressure, MongoDB aborts the oldest transaction. For details, see cachePressureQueryPeriodMilliseconds.

diagnosticDataCollectionDirectorySizeMB Parameter

MongoDB 8.3 increases the default value of diagnosticDataCollectionDirectorySizeMB from 200 to 500 MiB.

BSONObjectTooLarge Code for Upsert Errors

Starting in 8.3, upsert operations that produce a BSON object that is too large return the 10334 BSONObjectTooLarge error code. In earlier versions, upsert operations that produce a BSON object that is too large return the 17419 or 17420 error codes.

checkBSONConformance Field

Starting in 8.3, MongoDB no longer automatically enables the checkBSONConformance field in the db.collection.validate() method when full is true.

New Expression $subtype

MongoDB 8.3 introduces a new $subtype expression to extract the subtype of binary data objects.

New Expressions for Extended JSON Conversion

MongoDB 8.3 introduces new aggregation expressions for converting between BSON and Extended JSON (EJSON) format:

• $serializeEJSON - Converts BSON values to Extended JSON format with type wrappers. Supports both Canonical and Relaxed Extended JSON formats.

• $deserializeEJSON - Converts Extended JSON format back to native BSON values.

These expressions can be combined with $convert to parse JSON strings, transform Extended JSON values into native BSON values, and convert back to JSON format.

findShardsOnConfigTimeoutMS Parameter

MongoDB 8.3 adds the findShardsOnConfigTimeoutMS parameter which sets the timeout in milliseconds for find operations against the config.shards namespace. For details, see findShardsOnConfigTimeoutMS.

config.csrs.indexes Removed

MongoDB 8.3 removes the config.csrs.indexes namespace.

2dsphereIndexVersion

Starting in MongoDB 8.3, 2dsphereIndexVersion is set to version 4 by default.

If you need to downgrade the FCV to anything below 8.3, you must first drop the 2dsphere version 4 indexes.

refineCollectionShardKey Formatting

Starting in MongoDB 8.3, refineCollectionShardKey for time-series collections only accepts shard keys specified using the collection's logical meta and time fields. MongoDB no longer supports specifying keys using the underlying buckets format.

Index Naming Restrictions

Starting in MongoDB 8.3, creating an index with the name of "_id_" or specifying a hint of "_id_" on time series collections returns an error.

timeField Naming Restrictions

Starting in MongoDB 8.3, you cannot create a timeField that starts with a $ character.

Fields to Track Use of Memory by Queries

Starting in MongoDB 8.3, you can use the following new fields to track query memory use:

Both fields appear in the following places:

• $currentOp (Aggregation Stage) output

• db.currentOp() output

• Database profiler output

• Log messages

• Slow query log messages

The peakTrackedMemBytes field also appears in the following places:

• Explain results

• PlanCache.list() output

• $planCacheStats output

Mongos Query Shape Field

Starting in MongoDB 8.3, slow query log entries have an optional routerQueryShapeHash field that contains that query shape of the following operations that originate on the mongos :

• find

• aggregate

• count

• distinct