Release Notes for MongoDB 6.0

6.0.19 - Oct 24, 2024

• SERVER-96419 Improper neutralization of null bytes may lead to buffer over-reads in MongoDB Server

• All Jira issues closed in 6.0.19

• 6.0.19 Changelog

6.0.18 - Sep 30, 2024

• SERVER-70508 Add current thread count to extra_info in serverStatus on Linux

• SERVER-94166 Disable the SBE query engine in v6.0

• SERVER-94170 Revert SERVER-91570

• All Jira issues closed in 6.0.18

• 6.0.18 Changelog

6.0.17 - Aug 21, 2024

• SERVER-96254 CSFLE and Queryable Encryption self-lookup may fail to encrypt values in subpipelines

• SERVER-85892 $merge with pipeline after $documents returns error

• SERVER-91195 Provide a generic backportable solution not to miss top-level timeseries collection options

• SERVER-91362 Performance: Do not copy JS "scope" object if a cached JsExecution exists

• SERVER-91406 $changeStreamSplitLargeEvent returns Location7182803 error when used with non-renameable match expression

• WT-12708 Evaluation/Revision of eviction random traversal

• All Jira issues closed in 6.0.17

• 6.0.17 Changelog

6.0.16 - Jun 28, 2024

• SERVER-79637 Incorrect query results in $lookup with TS foreign collection using a correlated predicate

• SERVER-86474 $_internalApplyOplogUpdate with $set: { foo: Timestamp(0, 0) } is not replicated correctly

• SERVER-89625 Handle directoryPerDb and wiredTigerDirectoryForIndexes correctly when reporting namespaces and UUIDs during a backup

• WT-10807 Skip in-memory deleted pages as part of the tree walk

• WT-12609 Improve checkpoint cleanup and page eviction logic

• All Jira issues closed in 6.0.16

• 6.0.16 Changelog

6.0.15 - Apr 18, 2024

• SERVER-72703 Downgrade $out's db lock to MODE_IX

• SERVER-78556 Return default of internalInsertMaxBatchSize to 64

• SERVER-80363 server default writeConcern is not honored when wtimeout is set

• SERVER-83602 $or -> $in MatchExpression rewrite should not generate $or directly nested in another $or

• WT-11062 Safe free the ref addr to allow concurrent access

• All Jira issues closed in 6.0.15

• 6.0.15 Changelog

6.0.14 - Feb 28, 2024

• SERVER-82353 Multi-document transactions can miss documents when movePrimary runs concurrently

• SERVER-83119 Secondary replica crashes on clustered collection if notablescan is enabled

• SERVER-83145 Shared buffer fragment incorrectly tracks memory usage in freeUnused()

• SERVER-83564 Make sure the process field is indexed in config.locks

• WT-12077 Incorrect hardware checksum calculation on zSeries for buffers on stack

• All Jira issues closed in 6.0.14

• 6.0.14 Changelog

6.0.13 - Jan 18, 2024

• SERVER-33494 WT SizeStorer never deletes old entries

• SERVER-50792 Return more useful errors when a shard key index can't be found for shardCollection/refineCollectionShardKey

• SERVER-70155 Add duration of how long an oplog slot is kept open to mongod "Slow query" log lines

• SERVER-77506 Sharded multi-document transactions can mismatch data and ShardVersion

• SERVER-83091 $or query can trigger an infinite loop during plan enumeration

• All Jira issues closed in 6.0.13

• 6.0.13 Changelog

6.0.12 - Nov 27, 2023

• SERVER-69244 $merge fails when session default read concern has been set to "majority"

• SERVER-81295 Cannot resume V2 changeStream pipelines with V1 resume tokens

• SERVER-81966 Avoid modification of previous ChunkMap instances during refresh

• WT-7929 Investigate a solution to avoid FTDC stalls during checkpoint

• WT-11564 Fix RTS to read the newest transaction value only when it exists in the checkpoint

• All Jira issues closed in 6.0.12

• 6.0.12 Changelog

6.0.11 - Oct 11, 2023

• SERVER-58534 Collect fCV in FTDC

• SERVER-69244 $merge fails when session default read concern has been set to "majority"

• SERVER-71520 Dump all thread stacks on RSTL acquisition timeout

• SERVER-79498 Backport $vectorSearch to 6.0

• SERVER-80021 Make $convert round-trip correctly between double and string

• All Jira issues closed in 6.0.11

• 6.0.11 Changelog

6.0.10 - Sep 14, 2023

• SERVER-71627 Refreshed cached collection route info severely blocks all client request when a cluster contains 1 million chunks

• SERVER-73394 Remove misleading operationsBlockedByRefresh metrics

• SERVER-77183 $project followed by $group sometimes gives incorrect results

• SERVER-79771 Make resharding operations resilient to networkInterfaceExceededTimeLimit All Jira issues closed in 6.0.10

• 6.0.10 Changelog

6.0.9 - Aug 14, 2023

• SERVER-60466 Support drivers gossiping signed $clusterTimes to replica set --shardsvrs before addShard runs

• SERVER-74954 Incorrect result when contained $or rewrites $elemMatch extra condition

• SERVER-79136 Incorrect query result of $match + $group on metaField over time-series

• WT-10759 Do not retry to force evict history store pages during reconciliation

• WT-11064 Skip globally visible tombstones as part of update obsolete check

• All Jira issues closed in 6.0.9

• 6.0.9 Changelog

6.0.8 - Jul 13, 2023

• SERVER-61127 Multi-writes may exhaust the number of retry attempts in the presence of ongoing chunk migrations

• SERVER-77005 Leave LDAP users logged-in during LDAP downtime

• SERVER-78126 For specific kinds of input, mongo::Value() always hashes to the same result on big-endian platforms

• All Jira issues closed in 6.0.8

• 6.0.8 Changelog

6.0.7 - Jun 28, 2023

• SERVER-71985 Automatically retry time series insert on DuplicateKey error

• SERVER-73007 CURL_OPT_SEEKFUNCTION not set for multi-pass authentication

• SERVER-74551 WriteConflictException unnecessarily logged as warning during findAndModify after upgrade to mongo 5.0

• SERVER-77018 Deadlock between dbStats and 2 index builds

• WT-10449 Do not save update chain when there are no updates to be written to the history store

• WT-11031 Fix RTS to skip tables with no time window information in the checkpoint

• All Jira issues closed in 6.0.7

• 6.0.7 Changelog

6.0.6 - May 12, 2023

• SERVER-51835 Mongos readPreferenceTags are not working as expected

• SERVER-67105 $in queries do not use clustered index

• SERVER-72774 A node in quiesce mode can win election

• SERVER-74930 $avg is returning the sum instead of the average in aggregate $group

• SERVER-75205 Deadlock between stepdown and restoring locks after yielding when all read tickets exhausted

• All Jira issues closed in 6.0.6

• 6.0.6 Changelog

6.0.5 - Mar 13, 2023

Issues Fixed:

• SERVER-61909 Hang inserting or deleting document with large number of index entries

• SERVER-66469 Filtering timeseries with date-field does not include results from before 1970

• SERVER-68122 Investigate replicating the collection WiredTiger config string during initial sync

• SERVER-70395 Slot-Based Engine too aggressively uses disk for $group and is slow

• SERVER-73232 Change the default log-verbosity for _killOperations

• All JIRA issues closed in 6.0.5

• 6.0.5 Changelog

6.0.4 - Jan 26, 2023

Issues Fixed:

• SERVER-72416 The find and findAndModify projection code does not honor the collection level collation

• SERVER-71759 dataSize command doesn't yield

• SERVER-70237 Chunks merge commit must not create a BSON object too large

• SERVER-72222 mapReduce with single reduce optimization fails when merging results in sharded cluster

• WT-9268 Delay deletion of the history store record to reconciliation

• All JIRA issues closed in 6.0.4

• 6.0.4 Changelog

6.0.3 - Nov 21, 2022

Issues fixed:

• SERVER-66289 $out incorrectly throws BSONObj size error on v5.0.8

• SERVER-68139 Resharding command fails if the projection sort is bigger than 100MB

• SERVER-68371 Enabling CSFLE in your MongoClient causes Atlas Search to fail

• SERVER-68115 Bug fix for "elemMatchRootLength > 0" invariant trigger

• SERVER-68394 Ensure we do not yield strong locks upon startup recovery when _id index is missing

• All JIRA issues closed in 6.0.3

• 6.0.3 Changelog

6.0.2 - Sep 28, 2022

Issues fixed:

• SERVER-68925 Reintroduce check table logging settings at startup (revert SERVER-43664)

• SERVER-68628 Retrying a failed resharding operation after a primary failover can lead to server crash or lost writes

• SERVER-63852 getThreadName() should not crash

• SERVER-65317 mongod removes connection from connection pool after running simple $search query

• SERVER-63843 Don't allow recursive doLog in synchronous signal handlers

• WT-9870 Fix updating pinned timestamp whenever oldest timestamp is updated during recovery

• All JIRA issues closed in 6.0.2

• 6.0.2 Changelog

6.0.1 - Aug 19, 2022

Issues fixed:

• SERVER-68511 MovePrimary update of config.databases entry must use dotted fields notation

• SERVER-68062 Multi-stage aggregations that use $geoNear may violate constraints

• SERVER-66072 $match sampling and $group aggregation strange behavior

• SERVER-68130 AutoSplitVector could generate response bigger than BSONObjMaxUserSize

• SERVER-68209 Remove uassert that prevents config.image_collection entry from being invalidated

• All JIRA issues closed in 6.0.1

• 6.0.1 Changelog

6.0.0 - Jul 19, 2022

The rest of this page describes changes and new features introduced in MongoDB 6.0.

New Aggregation Stages

MongoDB 6.0 introduces the following aggregation stages:

New Aggregation Operators

MongoDB 6.0 introduces the following aggregation operators:

$lookup and $graphLookup with Sharded Collections

Starting in MongoDB 5.1, the $lookup and $graphLookup aggregation stages support sharded collections in the from parameter.

In previous versions of MongoDB, $lookup and $graphLookup only allowed for unsharded from collections.

You cannot use the $graphLookup stage within a transaction while targeting a sharded collection.

Optimized Change Streams

Starting in MongoDB 5.1, change streams are optimized, providing more efficient resource utilization and faster execution of some aggregation pipeline stages.

wallTime Change Stream Output Field

Starting in MongoDB 6.0, the change stream output has a new wallTime field that contains the server date and time of the database operation.

Change Streams with Document Pre- and Post-Images

Starting in MongoDB 6.0, you can use change streams to output the version of a document before and after changes (the document pre- and post-images). For examples, see Change Streams with Document Pre- and Post-Images.

Change Stream Expanded Events

Starting in MongoDB 6.0, change streams can show additional change events for DDL operations, like creating indexes and dropping collections.

For more information, see Expanded Events.

Filters

Starting in MongoDB 6.0, whenever possible, match filters are applied to change streams earlier than in prior releases. This improves performance. However, when a filter is narrowly defined, an earlier match may cause an operation that succeeds in prior versions to fail in 6.0.

Cluster Server Parameters

Starting in MongoDB 6.0, you can use Cluster Parameters for a Self-Managed Deployment to modify and retrieve configuration options for all nodes in a replica set or sharded cluster. You can use setClusterParameter to modify cluster-wide options and getClusterParameter to retrieve the value of a cluster parameter.

Connection Pool Parameters

Starting in MongoDB 6.0, you can use ShardingTaskExecutorPoolMinSizeForConfigServers and ShardingTaskExecutorPoolMaxSizeForConfigServers to set the minimum and maximum sharding TaskExecutor connection pool size for configuration servers.

changeStreamOptions Cluster Parameter

Starting in MongoDB 6.0, you can use changeStreamOptions to control the retention policy of change stream pre- and post-images.

internalSessionsReapThreshold Parameter

Starting in MongoDB 6.0, you can use the new internalSessionsReapThreshold parameter to set the session limit for internal session metadata deletion.

Multiple Arbiters Unsupported

Starting in MongoDB 5.3, support for multiple arbiters in a replica set is disabled by default. To enable support for multiple arbiters, start each node with the allowMultipleArbiters parameter.

Partial Indexes

Starting in MongoDB 6.0, you can use the operators $in and $or to create partial indexes. The partialFilterExpression maximum depth is also expanded from 2 to 4. You can now use the operators $and and $or at non-top-levels.

SELinux Policies

Starting in MongoDB 5.1, there is a new SE Linux Policy for:

• MongoDB Enterprise Server

• MongoDB Community Edition Server

running on Red Hat Linux. The SELinux policy is for use with default installations using rpm installer packages.

Multiple Arbiters Unsupported

Starting in MongoDB 5.3, support for multiple arbiters in a replica set is disabled by default. To enable support for multiple arbiters, start each node with the allowMultipleArbiters parameter.

initialSyncMethod Parameter

Starting in MongoDB 5.2, the initialSyncMethod determines whether initial sync is a logical initial sync or a file copy based initial sync.

initialSyncMethod is only available in MongoDB Enterprise Server.

Specify Secondary Oplog Batch Delay

Starting in MongoDB 6.0, you can use the oplogBatchDelayMillis server parameter to specify a delay for writes of oplog batches on secondaries. Adding a short oplog batch delay can reduce IOPS on secondaries, but adds latency for writes with write concern "majority".

For more information, see oplogBatchDelayMillis.

Audit Log Encryption

Starting in MongoDB 6.0 Enterprise, you can encrypt the MongoDB audit log.

To configure the audit log, see Audit Log.

Balancing Policy Changes

Starting in MongoDB 6.0.3, data in sharded clusters is distributed based on data size rather than number of chunks. Be aware of the following significant changes in sharded cluster data distribution behavior:

• The balancer distributes ranges of data rather than chunks. The balancing policy looks for evenness of data distribution rather than chunk distribution.

• Chunks are not subject to auto-splitting. Instead, chunks are split only when moved across shards.

• A chunk is now referred to as a range.

• moveRange has replaced moveChunk.

Default Chunk Size Increased from 64 MB to 128 MB

Starting in MongoDB 5.2, the default chunk size is 128 megabytes. In earlier versions of MongoDB, the default chunk size is 64 megabytes.

enableSharding No Longer Required

Starting in MongoDB 6.0, the enableSharding command is no longer required to shard a collection.

Monitor Defragmentation Status

Starting in MongoDB 5.3, the balancerCollectionStatus command returns detailed information when run on a namespace going through chunk defragmentation. The output includes the current phase of the defragmentation and how many chunks are left to process.

To see example output, see Ongoing Defragmentation Process.

Slot-Based Query Execution Engine Can Execute $group and $lookup Stages

Starting in version 6.0, MongoDB uses the slot-based query execution engine to execute eligible $group and $lookup stages when certain conditions are met.

For more information, see Slot-Based Query Execution Engine Pipeline Optimizations.

Set Slot-Based Query Execution Engine Plan Cache Size

You can set the size of the plan cache for the new query engine with the planCacheSize parameter.

Increasing the plan cache size adds more cached plan cache query shapes for the query planner. This can improve query performance, but increases memory usage.

Database Commands

Starting in MongoDB 6.0, the following database commands are supported in the Stable API:

Aggregation Stages and Operators

Starting in MongoDB 6.0, the following aggregation stages and operators are supported in the Stable API:

Sharded Time Series Collections

MongoDB 5.1 provides support for sharded time series collections.

See:

• Shard a Time Series Collection

• shardCollection

• Time Series Limitations

Updates and Deletes

Starting in MongoDB 5.1, time series collections support update and delete operations with limitations.

Time Series Column Compression

Starting in MongoDB 5.2, time series collections use column compression. Column compression adds a number of innovations that work together to significantly improve practical compression, reduce your data's overall storage on disk, and improve read performance.

Starting in MongoDB 6.0, arrays are also compressed as part of the time series column compression.

Support for $geoNear

Starting in MongoDB 5.3, you can use the $geoNear pipeline operator on any field in a time series collection.

Additional Secondary Index Types

Starting in MongoDB 6.0, you can perform the following operations on time series collections:

• Add additional secondary index types to time series collections, including 2dsphere and 2d indexes.

• Add a compound index on the timeField, metaField, or measurement fields.

• Use the $or, $in, and $geoWithin operators with partial indexes on a time series collection.

• Add a partial filter expression on the metaField.

• Use the metaField with 2dsphere indexes.

Sort Operations Use Secondary Indexes

Sort operations on time series collections can use indexes to improve performance. For more information and an example, see Use Secondary Indexes to Improve Sort Performance.

OpenSSL3 FIPS Support

Starting in MongoDB 6.0.7, FIPS mode supports OpenSSL3 for the following operating systems:

• Ubuntu 22.04

• RHEL 9

• Amazon Linux 2023

Starting in MongoDB 8.0, FIPS mode supports OpenSSL3 for Amazon Linux 2023.3.

Capped Collections Improvements

Starting in MongoDB 6.0, you can change a capped collection's maximum size, either in bytes or in number of documents, using the collMod command. See Resize a Capped Collection for more details.

numOrphanDocs Field Added to collStats Command

Starting in MongoDB 6.0, the collStats output includes the collStats.numOrphanDocs field that shows the number of orphaned documents in the collection.

Exclude Embedded Fields in serverStatus Output

Starting in MongoDB 6.0 (and 5.0.9), you can exclude embedded fields from the serverStatus output.

Connections

Starting in MongoDB 6.0, the Mongo() connection object has the following new methods:

• Mongo.getWriteConcern() returns the write concern

• Mongo.setWriteConcern() sets the write concern

Support for Diagnostic Backtrace Generation in arm64

Starting in MongoDB 6.0 (and 5.0.10), diagnostic backtrace generation in arm64 is supported.

Configure Refresh Interval for Cached LDAP User Information

Starting in MongoDB 5.2, you can use the following new server parameters to configure the refresh interval for cached LDAP user information:

• ldapUserCacheRefreshInterval

• ldapUserCacheStalenessInterval

• ldapShouldRefreshUserCacheEntries

Starting in MongoDB 5.2, the update interval for cached user information retrieved from an LDAP server depends on ldapShouldRefreshUserCacheEntries:

• If true, use ldapUserCacheRefreshInterval.

• If false, use ldapUserCacheInvalidationInterval.

Support for $group Stage in Explain Results

Starting in MongoDB 5.2, the Explain Results support the $group stage (GROUP), which separates documents into groups according to a group key, in the stage field.