Tests are run using https://github.com/idealo/mongodb-performance-test.git: java -jar ./latest-version/mongodb-performance-test.jar -m insert -o 10000000 -t 100 -db test -c perf -port 28888 -h mongoserver When running 4.0.6 standalone server with: {{docker run -ti -v /srv/mongo/test-mongo:/srv/mongodb/ --net host mongo:4.0.6 mongod --bind_ip_all --port=28888 --storageEngine=wiredTiger --dbpath=/srv/mongodb/ --journal --oplogSize=8192 --enableMajorityReadConcern=0}} I got: mean rate = 174014.88 calls/second When I start as replica set (no other replicas added, just start with replSet and call rs.initiate(): {{docker run -ti -v /srv/mongo/test-mongo:/srv/mongodb/ --net host mongo:4.0.6 mongod --bind_ip_all --port=28888 --storageEngine=wiredTiger --dbpath=/srv/mongodb/ --journal --oplogSize=8192 --enableMajorityReadConcern=0 --replSet wtf}} I got: mean rate = 44243.62 calls/second Huge drop, but fine, RS is enabled. Now let’s try it with 4.2.8: {{docker run -ti -v /srv/mongo/test-mongo:/srv/mongodb/ --net host mongo:4.2.8 mongod --bind_ip_all --port=28888 --dbpath=/srv/mongodb/ --enableMajorityReadConcern=0:}} mean rate = 167455.01 calls/second and same with replset enabled: {{docker run -ti -v /srv/mongo/test-mongo:/srv/mongodb/ --net host mongo:4.2.8 mongod --bind_ip_all --port=28888 --dbpath=/srv/mongodb/ --enableMajorityReadConcern=0 --replSet wtf:}} mean rate = 10868.81 calls/second Huge drop to 10kcalls/second.   I've made git bisect and identified these commits which drags performance down the most: b2384a85f62431d88ac01067ae4d1d3dbb4fede5 mean rate = 103095,21 calls/second 4cee07d8a97bb0663e7bfbc3f2e1fbf539140adf is the first bad commit commit 4cee07d8a97bb0663e7bfbc3f2e1fbf539140adf Author: Judah Schvimer <judah@mongodb.com> Date: Mon May 21 18:52:55 2018 -0400 SERVER-35113 Allow single voting primaries to advance stable timestamp even when last applied does not advance :040000 040000 948822d607a4ae02c4b18c9eac471e123fae892d 66d95e2b3a7fbdfda5aff07b58799dc8af359f3e M jstests :040000 040000 053e1a2ae25ef2e2599f2f89ad7a580a6509b2b3 cbf9ce44531ec2908fc8f5ee8cc0e569356dfffb M src drags down to mean rate = 22841,24 calls/second   Second: >>>>>> bcaa4eb01c mean rate = 37827,93 calls/second e4b08de746ef4e472bfdd4790fdb2b89d5a62f1a is the first bad commit commit e4b08de746ef4e472bfdd4790fdb2b89d5a62f1a Author: Lingzhi Deng <lingzhi.deng@mongodb.com> Date: Mon Apr 29 12:09:48 2019 -0400 SERVER-40462 : Disallow transactions on shard servers with writeConcernMajorityJournalDefault = false :040000 040000 e98acae85e9e9e09dc773dd464be513376791c96 bda8f41ecf04f82c70c8c2bc42dcdc3375b9e656 M jstests :040000 040000 0819f92e0a939abe440863dcc060aa48b7fcb128 752ad757384381fc777490bbca2c4f570c7aeec4 M src >>>>>>>> bcde4c4fd3 mean rate = 26577,37 calls/second   3rd: 86efdd6b047927d3a37577a6033bacc709c7ae89 is the first bad commit commit 86efdd6b047927d3a37577a6033bacc709c7ae89 Author: Ben Caimano <ben.caimano@mongodb.com> Date: Mon Dec 16 21:39:41 2019 +0000 SERVER-43945 Expose out of order latch acquisitions in serverStatus This review does several related things: Modifies the Mutex type to have one Identity object per invocation context Adds a latchAnalysis field to serverStatus Officially turns on CI-only failure for acq level violations Changes a few acq level declarations to be more permissive :040000 040000 cc0ee8580816f86084bcdab28f8ae92ec9da2bf1 a77afd98d1fa56c79b71de4ec7835e4905a9c664 M jstests :040000 040000 c9d93da9281647969dea4d505776120c9262a4d9 c2c56acf209149bdede17b97e7c3aadc2c882d1d M src 574b62017cad311690eba012222459ff5e41e8c5 mean rate = 11348,16 calls/second