MongoDB Diagnostics and Debugging (Version 3.4)
ch2 Tooling Overview

tags: MongoDB University M312

Introduction to Diagnostic and Debugging Tools

MongoDB tools

• mongostat - shows incoming operation in real time.
• mongotop - to know which collection we're spending time reading from and writing to.
• mongoreplay - to monitor record and replay network traffic
• mongo
• profiler - logs queries
• compass
• mtools

Introducing Server Logs

Server Log Components

• ACCESS
• COMMAND
• CONTROL
• GEO
• INDEX
• NETWORK
• QUERY
• REPL
• SHARDING
• STORAGE
• JOURNAL
• WRITE

Level Description

F fatal
E error
W warning
I information, for Verbosity Levels of 0
D Debug, for All Verbosity Levels >

You can always run your system with maximum verbosity, if you wanted to capture more infomation.

mongod -vvvvv

currentOp and killOp

• currentOp - Shows what the server doing, the current operation

db.currentOp()

• killOp - To kill a operation

db.killOp(<opID>)

Introducing Server Status

db.serverStatus()

Although db.serverStatus() gives us a huge information, the output can be grouped into a few different sections.

List of Topics

• Instance Information
• Asserts
• Connections and Network
• Locking
• Operation stats
• Security
• Replication stats
• Storage Engine stats
• Metrics

We can do the projection of output like this

db.runCommand( { serverStatus: 1, repl: 0, metrix: 0, lock: 1, wireTiger: 0} )

To check key of the command by js function

Object.keys(serverStatus())

The output example of serverStatus

// operation counter
db.serverStatus().opcounters.insert
db.serverStatus().opcounterRepl
// host name
db.serverStatus().host

// version number
db.serverStatus().version

// process mongod or mongos
db.serverStatus().process

// process id
db.serverStatus().pid

// how long server is running
db.serverStatus().uptime

db.serverStatus().uptimeMillis

// local time
db.serverStatus().localtime

// current establish connection
db.serverStatus().connections

// assertion errors raised since the server process started
db.serverStatus().asserts

// operation latency
db.serverStatus().opLatencies

Introducing the Profiler

Turnning profiler on, every operation comming in will be stored in system.profile collection.

The collection size is 1 megabyte by default and is a capped collection.

It's better to turn off if there was no special needs.

// show the profiler level
db.getProfilingLevel()

// set profiler level
db.setProfilingLevel()

level:
0: not capture any query
1: capture queries that take longer than 100ms
2: capture all queries

Server Diagnostic Tools

• bsondump
• mongo
• mongod
• mongodecrypt
• mongodump
• mongoexport
• mongofiles
• mongoimport
• mongoldap
• mongooplog
• mongoperf
• mongoreplay
• mongorestore
• mongos
• mongostat
• mongotop

$indexStats

We can get the usage frequency by using the aggreation.

DOC