MongoDB 4.2.3

What's new in this version:

Security:
- User acquisition shouldn’t increment cache generation
- Ensure bind credentials live longer than LDAP operations

Sharding:
- Make allow_partial_results.js, return_partial_shards_down.js start shards as replica sets
- Add namespace to ChunkManager ShardKeyNotFound failure in order to better diagnose failures.
- sharding_balance4.js should wait for ongoing chunk splits between updates
- Shards do not treat the IGNORED version as “intended sharded”
- Make the BatchWriteExecutor retry multi-writes only against unsuccessful shards
- Remove assertions about the last-stable behavior in allow_partial_results.js and return_partial_shards_down.js

Replication:
- ReplicationCoordinatorExternalState and data replication must not be started after shutdown
- Log metrics.repl.stepDown counters after stopped killing user operations as part of state transition (step up/ step down).
- Initial sync may crash due to missing oplog entries of running transactions
- Race while setting replication maintenance mode.
- Race in replsets/auth2.js
- Write the temp file of rollback file dump in the test’s db directory
- Increased vulnerability to slow DNS
- Use awaitMajorityCommitted in standalone_replication_recovery_idempotent.js
- fix the “me” field in isMaster responses when using splithorizon

Query:
- Replace queryoptimizer3.js with FSM test
- Disallow the empty string as an index key type
- Aggregations and find commands sort missing fields differently
- Allow change stream with updateLookup to run directly against a shard mongoD in a sharded cluster
- Negation of inequality on array can trip invariant

Aggregation:
- Add more testing for special values in DoubleDoubleSummation
- $push and $addToSet should restrict memory usage
- Change stream should throw ChangeStreamFatalError if a single shard cannot be targeted for updateLookup
- Add query knob to control memory limit for $push and $addToSet
- Not-equal ($ne) in query for mapReduce causes segmentation fault

Storage:
- Coverity analysis defect 101508: Data race condition
- Check for duplicate namespaces when dumping catalog
- Formalize contract for safely accessing the catalog
- include Client/OpCtx information in LockManager::dump() output
- BtreeKeyGenerator::_extractNextElement() uassert message exceeds 16mb BSON document limit when added to a command result
- Adjust nojournal startup warning to be more compelling

WiredTiger:
- Performance regression in indexes with keys with common prefixes

Operations:
- Remove upstream metadata from v4.2’s third party library manifest

Build and Packaging:
- Remove mobile specific build and code artifacts
- Remove mobile specific embedded commands
- Set an explicit default for the SCons MSVC_VERSION flag
- Ubuntu 18.04 package testing task fails to install openssl

Tools:
- Use –forceTableScan by default when running against WiredTiger nodes
- Backport ‘TOOLS-2403 mongorestore hang while replaying last oplog failed in archive mode’
- Backport TOOLS-1952 to 4.2
- Index keys not escaped correctly
- Backport

Internals:
- Relax expectations in apply_batches_totalMillis
- Expose tcmalloc_release_rate via setParameter
- jstests/sharding/kill_sessions.js doesn’t wait for operation to be killed
- Add a log line for when a cursor is reaped due to logical session cleanup
- mongos tries to connect to the secondary to create the index if rs.slaveOk() is set
- Incorrect serialization for $elemMatch $not $ne
- Fix tls_enumerators.py from BF-14793
- Add new “one-click” genny workload tasks to system_perf.yml
- Map reduce with mode “merge” to an existing sharded collection may drop and recreate the target if no docs exist on the primary shard
- Update the embedded version of the server’s timezone data file to tzdb-2019c
- Linux shutdown of mongod sometimes never completes
- Make FailPoint::pauseWhileSet increment _timesEntered once
- Correct logic to re-compute dependencies after absorbing a $sort into query layer
- [4.2] Calculate index build memory usage per key based on BSONObj buffer capacity, not size
- Change Windows Kerberos client to use default credentials when no password is specified
- Use longer retry for kms service
- Remove evergreen client from buildscripts
- Ensure RoleGraph can serialize authentication restrictions to BSON
- Backport ‘TOOLS-1826 mongorestore panic in archive mode when replay oplog failed’
- Add debug mode which allocates exact amount of memory in __wt_realloc_def
- Add debug mode option that slows checkpoint creation
- Remove lsm_merge configuration option
- Migrate Jenkins “wiredtiger-test-check-long” job to Evergreen
- Migrate Jenkins “wiredtiger-test-format-stress” job to Evergreen
- Migrate Jenkins “wiredtiger-test-format-stress-ppc” job to Evergreen
- Migrate Jenkins “wiredtiger-test-format-stress-sanitizer” job to Evergreen
- Migrate Jenkins “wiredtiger-test-checkpoint-stress” job to Evergreen
- Migrate Jenkins “wiredtiger-test-recovery-stress” job to Evergreen
- Migrate Jenkins “wiredtiger-test-split-stress” job to Evergreen
- Move Application Developer Resources documentation in github to WT documentation
- Log more information when timestamp usage issue is encountered
- Always return WT_TRY_SALVAGE for corrupted log
- Handle ENOENT without failure when copying the directory
- Application threads are tasked with eviction even when pinning the oldest transaction ID
- Log a message when rolling a thread back because it holds the oldest timestamp
- Handling goto labels with multiple words in s_goto.py
- Checkpoint hangs when reconciliation doesn’t release the eviction generation
- WiredTiger incremental backup API
- Bypass test_wt2853_perf in Evergreen make-check-msan-test
- Create a wrapper script to support format stress tests in Evergreen
- Coverity analysis bug: 113971 Dereference after null check
- Prepared updates written to the lookaside file are not always read as needed
- format.sh must handle core-dump signals and “gdb attach” build mode
- test/format needs to move the oldest timestamp forward during bulk load
- Cursor key out-of-order detected in the lookaside file
- format.sh must distinguish format timeouts and kill child processes
- format.sh must handle format’s use of the wt utility
- Update format.sh script to add prefix command argument
- Format timestamps identically to MongoDB
- Add thread doing random cursor operations to format’s cache size calculation
- Avoid loading extensions that have blank name for Python tests
- Avoid clearing the saved last-key when no instantiated key
- WiredTiger API error handling fixes
- Backup cursor API can fail to restore WT_SESSION name information
- Read-only transactions are being rolled back in MongoDB
- Add a template for building a glossary in developer docs
- Remove format’s long-running transaction support