Kernel Version Description

This section describes the kernel version updates of Document Database Service (DDS). Thisupgrade does not affect any functions or APIs.

**Table 1** DDS 4.4 version updates
Version	Date	Description
4.4	June 2024	Both localField and foreignField can be specified when pipeline is specified for lookup. Resolved the issue that setLogLevel shields storage layer logs. Indexes can be specified using hints during update.
	May 2024	Optimized the CPU usage of changeStream. Resolved the problem that backup errors may occur when tables are deleted during backup. Added the effectiveUsers field to the query result of the db.currentOp() command. Supported mongo exporter.
	April 2024	Supported sharded tables for $lookup. Supported $startAfter for changeStream. Optimized the performance of distributed transactions in shard primary/standby switchover scenarios.
	March 2024	Resolved the problem that fields output by setWindowFields are missing.
	February 2024	Optimized the read performance of changeStream. Optimized the performance of clearing expired oplog data. Resolved the problem that geoNear is not displayed when explain() is executed.
	January 2024	Resolved the problem that there is a possibility that regular expression matching fails.
	December 2023	Optimized the performance of querying a single document. Restricted the permission to run a risky reIndex command.
	November 2023	Resolved the problem that the command output is not displayed on the memory monitoring page after a command is executed.
	October 2023	Optimized the method for obtaining locks by running the ServerStatus command. Resolved the problem that there is a possibility that a secondary node fails to be promoted.
	September 2023	Supported index and collection creation in multi-document transactions. Supported autosplit setting for a single collection. Fixed the bug that the performance is inconsistent with that of MongoDB 4.4 when you create sparse indexes and set find to null.
	August 2023	Added the capability for proactively limiting the number of connections. Added the compatibility with Parallel Change Stream. Fixed the bug that aggregation commands can still be executed on cluster instances when read and write operations are disabled. Optimized the method for capturing slow query logs.
	July 2023	Optimized the compression algorithm of the storage engine. Automatically routed the CreateIndex command to the primary node for execution. Optimized the passive compact synchronization logic.
	May 2023	Added totalTimeProcessingMicros, processingMethod, totalTimeTruncatingMicros and truncateCount to oplogTruncation in serverStatus.
	April 2023	Optimized the transaction execution logic.
	March 2023	Added automatic storage failover. Supported the defaultReadWriteConcern for replica set instances. Supported Point-In-Time Recovery (PITR) for cluster instances.
	January 2023	Optimized the tcmalloc memory management policy. Supported distributed large transactions.
	November 2022	Added the compound hash index. Added the mutable shard key values. Added the compatibility with mirrored reads.

**Table 2** DDS 4.2 version updates
Version	Date	Description
4.2	June 2024	Resolved the issue that setLogLevel shields storage layer logs.
	May 2024	Optimized the CPU usage of changeStream. Added the effectiveUsers field to the query result of the db.currentOp() command. Supported mongo exporter.
	April 2024	Optimized the performance of distributed transactions in shard primary/standby switchover scenarios.
	March 2024	Supported the startAfter feature.
	February 2024	Optimized the read performance of changeStream. Optimized the performance of clearing expired oplog data. Resolved the problem that geoNear is not displayed when explain() is executed.
	January 2024	Resolved the problem that there is a possibility that regular expression matching fails.
	December 2023	Optimized the performance of querying a single document. Restricted the permission to run a risky reIndex command.
	November 2023	Resolved the problem that the command output is not displayed on the memory monitoring page after a command is executed.
	October 2023	Optimized the method for obtaining locks by running the ServerStatus command. Resolved the problem that there is a possibility that a secondary node fails to be promoted.
	September 2023	Supported index and collection creation in multi-document transactions. Supported autosplit setting for a single collection.
	August 2023	Added the capability for proactively limiting the number of connections. Fixed the bug that certain sessions are occasionally killed when there are locks. Optimized the method for capturing slow query logs.
	July 2023	Optimized the compression algorithm of the storage engine. Automatically routed the CreateIndex command to the primary node for execution. Optimized the passive compact synchronization logic. Fixed the bug that the system session table occasionally fails to be updated due to the MongoDB open-source community vulnerability SERVER-39044.
	June 2023	Optimized the performance of the update operation on a 10 KB document in a replica set. Fixed the SERVER-37408 vulnerability. Fixed the SERVER-39074 vulnerability.
	May 2023	Resolved the writeConcern error code matching issue after a primary/standby switchover.
	April 2023	Optimized the transaction execution logic. Fixed the bug that the execution of dropIndexes() with specified parameters is inconsistent with that of MongoDB 4.2. Fixed the bug that the restart is slow when emrc is set to true and dirty cache increases.
	March 2023	Added automatic storage failover. Reduced the primary/secondary replication delay. Supported Point-In-Time Recovery (PITR) for cluster instances.
	January 2023	Supported distributed large transactions. Fixed the SERVER-42518 vulnerability. Fixed the SERVER-37686 vulnerability.
	November 2022	Fixed the bug that MongoDB Compass occasionally fails to be connected through SSL. Fixed the bug that the performance is inconsistent with that of MongoDB 4.2 when find is set to null.
	October 2022	Added index consistency check. Fixed the CVE-2020-7921 vulnerability.
	September 2022	Supported index creation in the background by default. Opened the replSetGetConfig command.
	June 2022	Supported the ZSTD compression algorithm. Supported the releaseFreeMemory command for mongos nodes.

**Table 3** DDS 4.0 version updates
Version	Date	Description
4.0	June 2024	Supported mongo exporter.
	May 2024	None
	April 2024	None
	March 2024	None
	February 2024	Resolved the problem that geoNear is not displayed when explain() is executed.
	January 2024	Resolved the problem that there is a possibility that regular expression matching fails.
	December 2023	Optimized the performance of querying a single document. Restricted the permission to run a risky reIndex command.
	November 2023	None
	October 2023	Optimized the method for obtaining locks by running the ServerStatus command. Resolved the problem that there is a possibility that a secondary node fails to be promoted.
	September 2023	Optimized the resizeOplog logic.
	August 2023	Fixed the bug that aggregation commands can still be executed on cluster instances when read and write operations are disabled. Fixed the bug that certain sessions are occasionally killed when there are locks. Optimized the method for capturing slow query logs.
	July 2023	Automatically routed the CreateIndex command to the primary node for execution. Optimized the passive compact synchronization logic. Fixed the bug that the system session table occasionally fails to be updated due to the MongoDB open-source community vulnerability SERVER-39044. Fixed the bug that NotMaster is displayed when a cluster instance is connected using Robot 3T and readPreference is set to secondaryPreferred by default.
	June 2023	Provided the enableCheckPassword parameter to enable or disable password complexity check. Optimized the index deletion procedure to improve efficiency.
	May 2023	Fixed the SERVER-37408 vulnerability. Fixed the SERVER-39074 vulnerability.
	April 2023	Fixed the bug that the execution of dropIndexes() with specified parameters is inconsistent with that of MongoDB 4.2. Fixed the bug that the restart is slow when emrc is set to true and dirty cache increases.
	March 2023	Added automatic storage failover. Fixed the CVE-2018-20805 vulnerability.
	January 2023	Fixed the SERVER-42518 vulnerability. Fixed the SERVER-37686 vulnerability.
	November 2022	Fixed the bug that MongoDB Compass occasionally fails to be connected through SSL.
	October 2022	Added index consistency check. Fixed the CVE-2020-7921 vulnerability.
	July 2022	Supported index creation in the background by default. Opened the replSetGetConfig command.
	June 2022	Supported the releaseFreeMemory command for mongos nodes.

**Table 4** DDS 3.4 version updates
Version	Date	Description
3.4	June 2024	None
	May 2024	None
	April 2024	Optimized aggregate query and supported mapping adding for $project.
	March 2024	None
	February 2024	None
	January 2024	None
	December 2023	Restricted the permission to run a risky reIndex command.
	November 2023	None
	October 2023	Optimized the method for obtaining locks by running the ServerStatus command.
	September 2023	Displayed detailed slow query log information.
	August 2023	Fixed the bug that aggregation commands can still be executed on cluster instances when read and write operations are disabled. Fixed the bug that certain sessions are occasionally killed when there are locks. Optimized the method for capturing slow query logs.
	July 2023	Synchronized ReleaseFreeMemory to version 3.4.
	May 2023	Fixed the SERVER-37408 vulnerability. Fixed the SERVER-39074 vulnerability.
	April 2023	Fixed the bug that the activeSession on the standby config node in a cluster is not updated in a timely manner.
	March 2023	Added automatic storage failover. Fixed the CVE-2018-20805 vulnerability.
	January 2023	Fixed the SERVER-42518 vulnerability. Fixed the SERVER-37686 vulnerability.
	October 2022	Fixed the CVE-2020-7921 vulnerability. Fixed the bug that the value of heapprofile is incorrect.
	July 2022	Resolved the weak password verification issue.
	June 2022	Supported mongos log anonymization.