MongoDB 8.2.0

What's new in this version:

- MongoDB 8.2 is a Minor Release, which means that it is supported for both MongoDB Atlas and on-premises deployments. MongoDB 8.2 introduces incremental improvements within a Major version release cycle. MongoDB 8.2 also includes changes introduced in MongoDB Rapid Release 8.1. This page describes changes introduced in the Rapid Release and MongoDB 8.2.

Sharding:
- terminateSecondaryReadsOnOrphanCleanup Parameter
- MongoDB 8.2 adds the terminateSecondaryReadsOnOrphanCleanup parameter, which controls whether long-running read operations on secondary nodes automatically terminate before orphaned document deletion following a chunk migration.
- By default, this parameter is set to true. If a read operation on a secondary node begins before the chunk migration commits, MongoDB automatically terminates the operation before deleting the orphaned documents. In MongoDB versions before 8.2, these operations continue executing after orphaned document deletion and may silently miss documents without returning an error.
- To support this new behavior, the default value for orphanCleanupDelaySecs is now 3600 (previously 900).

General Changes:
Index Builds During Initial Sync:
- Starting in MongoDB 8.2, index builds during initial sync use 10% of available RAM by default. You can specify a different percentage of memory for MongoDB to use with the initialSyncIndexBuildMemoryPercentage parameter.
- By default, the amount of available memory must be between 200 MB and 16 GB, inclusive. You use the following parameters to specify different minimum and maximum thresholds for memory usage:
- initialSyncIndexBuildMemoryMinMB
- initialSyncIndexBuildMemoryMaxMB

Query Statistics:
- Starting in MongoDB 8.2, the $queryStats output includes the following metrics on delinquent tickets:
- metrics.delinquentAcquisitions
- metrics.totalAcquisitionDelinquencyMillis
- metrics.maxAcquisitionDelinquencyMillis
- MongoDB considers an execution ticket as delinquent when acquisition takes too long.
- WiredTiger Cache Size Configuration as a Percentage
- Starting in MongoDB 8.2, you can configure the WiredTiger internal cache size using a new percentage-based option. In addition to the existing --wiredTigerCacheSizeGB and storage.wiredTiger.engineConfig.cacheSizeGB gigabyte-based settings, you can now specify the cache size as a percentage of the available memory with the --wiredTigerCacheSizePct and storage.wiredTiger.engineConfig.cacheSizePct options.
- New Inconsistency Type: Range Deletion Missing Shard Key Index
- Starting in MonogDB 8.2, a new inconsistency type RangeDeletionMissingShardKeyIndex is implemented. The inconsistency type indicates that a sharded collection exists that doesn't have an index compatible with the collection shard key and there is at least one remaining range deletion task to complete.
- New Aggregation Expression
- Starting in MongoDB 8.2, you can use $currentDate with aggregate() to return the current time on the server.

New $currentOp Field:
- The $currentOp aggregation stage now includes the versionContext field, which provides information on the Feature Compatibility Version (FCV) of the operation.

serverStatus Output Change:
- serverStatus includes the following new fields in its output:
- metrics.operation.killedDueToRangeDeletion
- metrics.query.bucketAuto.spilledBytes
- metrics.query.bucketAuto.spilledDataStorageSize
- metrics.query.bucketAuto.spilledRecords
- metrics.query.bucketAuto.spills
- planCache.classic.replanned_plan_is_cached_plan
- planCache.sbe.replanned_plan_is_cached_plan
- spillWiredTiger
- connections.queuedForEstablishment
- connections.establishmentRateLimit
- connections.establishmentRateLimit.rejected
- connections.establishmentRateLimit.exempted
- connections.establishmentRateLimit.interruptedDueToClientDisconnect
- metrics.network.averageTimeToCompletedTLSHandshakeMicros
- metrics.network.averageTimeToCompletedHelloMicros
- metrics.network.averageTimeToCompletedAuthMicros
- queues.ingressSessionEstablishment
- queues.ingressSessionEstablishment.addedToQueue
- queues.ingressSessionEstablishment.removedFromQueue
- queues.ingressSessionEstablishment.interruptedInQueue
- queues.ingressSessionEstablishment.rejectedAdmissions
- queues.ingressSessionEstablishment.exemptedAdmissions
- queues.ingressSessionEstablishment.successfulAdmissions
- queues.ingressSessionEstablishment.attemptedAdmissions
- queues.ingressSessionEstablishment.averageTimeQueuedMicros
- queues.ingressSessionEstablishment.totalAvailableTokens
- Explain Output for Disk Spilling Stages:
- Starting in MongoDB 8.2, the Explain Results for stages that spill to disk now include standardized metrics under consistent field names. This update provides a more unified way to track disk usage for memory-intensive operations.

The new fields include:
- spills
- spilledBytes
- spilledRecords
- spilledDataStorageSize

Repair Mode Field in Validation Output:
- Starting in MongoDB 8.2, the validate command and the db.collection.validate() helper method return a new repairMode field that indicates what types of data inconsistencies the validate command attempted to repair, if detected.

Support for zstd Fast Compression:
- Starting in MongoDB 8.2, The storage.wiredTiger.engineConfig.zstdCompressionLevel setting supports negative values for fast zstd compression. Negative values provide faster compression and decompression speeds at the cost of the compression ratio. The new supported range is -7 to 22.

Targeted Mirrored Reads:
- Starting in MongoDB 8.2, you can selectively mirror read operations to specific servers that need their caches warmed up by tagging the nodes for read mirroring. Unlike general mirrored reads, targeted read mirroring allows you to target hidden nodes and mirror from both primary and secondary nodes.
- You can configure targeted mirrored reads using the targetedMirroring field in the mirrorReads parameter.

Rate Limit Ingress Connection Establishment:
- Starting in MongoDB 8.2, you can enable rate limiting for ingress connections to preserve CPU resources during overload. When enabled, you can see when the rate of incoming connections exceeds the connection establishment rate they specified and configure parameters to specify how your MongoDB deployment handles excess connections.

You can configure rate limiting using the following new fields:
- ingressConnectionEstablishmentRateLimiterEnabled
- ingressConnectionEstablishmentRatePerSec
- ingressConnectionEstablishmentBurstCapacitySecs
- ingressConnectionEstablishmentMaxQueueDepth

Security:
Queryable Encryption Prefix, Suffix, and Substring Query Public Preview:
- Prefix, Suffix, and Substring Queries are in Public Preview
- Queryable Encryption prefix, suffix, and substring queries are available in public preview in MongoDB 8.2. Do not enable these query types in production. Public preview functionality will be incompatible with the GA feature, and you will have to drop any collections that enable these queries.
- MongoDB 8.2 lets you enable prefix, suffix, and substring queries on encrypted string fields in Queryable Encryption enabled collections. For details, see enable substring queries and Supported Aggregation Expressions.