Some useful MongoDB commands

Connection

Connect to node

mongo {Host}:{Port}/{DB} -u {User} -p{Password}

Sample: 
mongo localhost:27017/admin -u root -pPassword
mongo 127.0.0.1:27017/admin -u root -pPassword

Check connection status

db.serverStatus().connections

Check connection count group by IP address

db.currentOp(true).inprog.reduce(
  (accumulator, connection) => {
    ipaddress = connection.client ? connection.client.split(":")[0] : "Internal";
    accumulator[ipaddress] = (accumulator[ipaddress] || 0) + 1;
    accumulator["TOTAL_CONNECTION_COUNT"]++;
    return accumulator;
  },
  { TOTAL_CONNECTION_COUNT: 0 }
)

WiredTiger

Check WT cache status

db.serverStatus().wiredTiger.cache

Check WT available ticket status

db.serverStatus().wiredTiger.concurrentTransactions

Replication

Check replication members and their status

rs.status()

Check replication lags of nodes

rs.printSlaveReplicationInfo()

Check oplog size and log length in hours

rs.printReplicationInfo()

Check replication configuration

rs.config()

Failover to secondary/another node

# Run on PRIMARY Node
rs.stepDown()

Freeze slave node from becoming a master during the failover

# Run on SECONDARY node which need to freeze 
rs.freeze(no of seconds)

Profiling

Check Profiling Status

db.getProfilingStatus()

Enable Profiling

db.setProfilingLevel(1, { slowms: 100, sampleRate: 1 })

Disable Profiling

db.setProfilingLevel(0, { slowms: 100, sampleRate: 1 })

mtools

mongostat

mongostat -h {HostName/IP} -u {User} -p '{Password}' --port={Port} --authenticationDatabase=admin

Sample:
mongostat -h 127.0.0.1 -u root -p 'Password' --port=27018 --authenticationDatabase=admin

mongotop

mongotop -h {HostName/IP} -u {User} -p '{Password}' --port={Port} --authenticationDatabase=admin

Sample:
mongotop -h 127.0.0.1 -u root -p 'Password' --port=27018 --authenticationDatabase=admin

mlogfilter

# Get the list of collection scan whole collections 
mlogfilter mongod.log --planSummary=COLLSCAN

# Get the list of slow queries more than 1000ms
mlogfilter mongod.log --slow 1000

# Get the list of errors, warnings 
mlogfilter mongod.log  --word assert warning errors

# Get the specific namespace queries which are running more than 1000ms
mlogfilter mongod.log --namespace admin.\$cmd --slow 1000

mloginfo

mloginfo mongod.log  --queries

Shard

Check shard status

sh.status()

Stop Balancer

sh.stopBalancer()

Start Balancer

sh.startBalancer()

Note: We will keep updating this page, as long as we will have some new commands.