MongoDB Diagnostics and Debugging (Version 3.4)
Ch 4: Connectivity

tags: `MongoDB University M312`

What Connectivity Issues Look Like in an Application

Time Outs
Connection Error
Incorrect URI
Non-static IP Addresses
Firewall
Out of conrtrol
- DDoS attacks
- ISP Performing Poorly

Timeout

Timeout Errors

Server Selection TimeoutError
WTimeError ( 僅表示 writeConcern 沒有在時間內完成，不代表 query 沒有完成 )


db.foo.insertOne( {hello: 'world'}, { writeConcern: { w: 3, wtimeout: 2} } )

Execution Timeout


db.collection.find({})._addSpecial("$maxTimeMS", 100)

Network Timeout

Closing and Dropping Connections

Greedy Connection Applications
- Implication of Connection in Memory allocation
How to detect poorly configured hosts
Election of new Primary

Tools

Mongostat
db.serverStatus()
free -h (OS)
mongod log file

MongoDB allows incoming connections up to 65536.

Since our process require RAM, too many connections is not the normal behavior for a well written application.

net.maxIncomingConnections configuration file parameter affect the number of available incoming connections
Cuz one connection is regard as a file to mongod, we need to set higher limit for more connections.


# allow open file to 2048
ulimit -n 2048


// shows the available connections of mongod
db.serverStatus().connections

Election of Primary

Write Concern and Timeouts

Doc

Replica set with 'w:majority' may have some bad situation when there are arbiters or delay servers in the set.

Hostnames and Cluster Configuration

edit host file






# OS like
/etc/host

# windows
C:\WINDOWS\system32\drivers\etc\hosts

Networking Best Practices

All Replica Set nodes should be addressable from client hosts and replica set hosts
All mongos nodes should be addressable
Use DNS names instead of IP address to avoid IP address renew resolution conflicts
Make use of ping command to check if node can reach each other
- Use telnet to make sure that the ports are available

Sharding Issues

split chunk manually


sh.splitAt('m312.example', { last_name: 'E', first_name: Minkey })

Increase chunk size


use config
db.setting.save( { _id: 'chunksize', value: 150 } )

MongoDB Diagnostics and Debugging (Version 3.4)
Ch 5: Schema Issues

Schema Investigation

turn on the profiler


db.setProfilingLevel(2)

turn off the profiler and see how many queries were made


db.setProfilingLevel(0)
db.system.profile.count()

Get deeper information


db.system.profile.find({}, { planSummary: 1, op:1, ns: 1, query: 1 }).pretty()

MongoDB Diagnostics and Debugging (Version 3.4) Ch 4: Connectivity

tags: MongoDB University M312