Hi Team,

Recently we migrated from mongo 4.0.27 to 4.2.23. After the migration, we see the performance is degraded. Note that, the workload, client, storage engine, dbParameters , client driver version and  indexing remains same but, only the mongo version upgrade.

We have been running CRUD operations on a replica-set but with the 4.2 we see the response time is going high and clients timeouts (we set readTimeout/socketTimeout as 1200). Due to the slow response , we see the maxWaitQueueSize also exceeded resulting in dropping of the database request.

Again, with the same setup if we downgrade the mongo version alone, it performs better.  .

 

We understand there are many features introduced in mongo 4.2. We even tried changing the FeatureCompatibilityVersion to 4.0 on a mongod running with 4.2 but didn’t see any improvement.

 

To reiterate, both the test performed on the same setup so no change in HW,resources, dbparameters, Storage engine and the CRUD operations. 

 

Mongo- Server Version: 4.2.23

Mongo Client Java Driver version: 3.12.9

Standalone or Replica : Replica set PSA . Issues seen in 5 members replicaSet as well (4 data bearing + 1 arbiter)

Server Option: /usr/bin/mongod --ipv6 --slowms 500 --storageEngine wiredTiger --wiredTigerCacheSizeGB 8 --enableMajorityReadConcern false --bind_ip_all --port 27737 --dbpath=/var/data/sessions.1/3/set08 --replSet set08 --fork --pidfilepath /var/run/sessionmgr-27737.pid --oplogSize 5120 --logpath /var/log/mongodb-27737.log --logappend --quiet

Storage Engine : WT

dbPath : in RAMdisk/tmpfs

Replica-Set Config:

set08:PRIMARY> rs.conf()

{

        "_id" : "set08",

        "version" : 9,

        "protocolVersion" : NumberLong(1),

        "writeConcernMajorityJournalDefault" : false,

        "members" : [

                {

                        "_id" : 0,

                        "host" : "sessionmgr04:27737",

                        "arbiterOnly" : false,

                        "buildIndexes" : true,

                        "hidden" : false,

                        "priority" : 2,

                        "tags" :

{                           },

                        "slaveDelay" : NumberLong(0),

                        "votes" : 1

                },

                {

                        "_id" : 1,

                        "host" : "sessionmgr03:27737",

                        "arbiterOnly" : false,

                        "buildIndexes" : true,

                        "hidden" : false,

                        "priority" : 3,

                        "tags" : {                           }

,

                        "slaveDelay" : NumberLong(0),

                        "votes" : 1

                },

                {

                        "_id" : 2,

                        "host" : "arbitervip:27737",

                        "arbiterOnly" : true,

                        "buildIndexes" : true,

                        "hidden" : true,

                        "priority" : 0,

                        "tags" :

{                           }

,

                        "slaveDelay" : NumberLong(0),

                        "votes" : 1

                }

        ],

        "settings" : {

                "chainingAllowed" : true,

                "heartbeatIntervalMillis" : 2000,

                "heartbeatTimeoutSecs" : 1,

                "electionTimeoutMillis" : 10000,

                "catchUpTimeoutMillis" : -1,

                "catchUpTakeoverDelayMillis" : 30000,

                "getLastErrorModes" :

{                   }

,

                "getLastErrorDefaults" :

{                         "w" : 1,                         "wtimeout" : 0                 }

,

                "replicaSetId" : ObjectId("636d3c916a35f79c756653c8")

        }

}

Please give us the portal link to upload the mongotop,stat,logs and diagnostics.data.