Difference between revisions of "MongoDB"

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== Install MongoDB on ubuntu ==
+
 
 +
= Install =
 +
From: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-os-x/
 +
 
 
From: https://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/
 
From: https://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/
  
−
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927
+
From: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-red-hat/
−
echo "deb http://repo.mongodb.org/apt/ubuntu trusty/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list
+
 
−
sudo apt-get update -y
+
 
−
sudo apt-get install -y mongodb-org
+
 
 +
= Develop =
 +
 
 +
== rename a field, or paste one field to another collection-wide ==
 +
 
 +
Methods are: updateOne, updateMany or update
 +
<pre>
 +
db.collection.<update method>(
 +
    {},
 +
    [
 +
        {"$set": {"name": { "$concat": ["$firstName", " ", "$lastName"]}}}
 +
    ]
 +
)
 +
</pre>
  
 
== Count Documents ==
 
== Count Documents ==
Line 16: Line 32:
 
</pre>
 
</pre>
  
−
== Performance Tuning ==
+
== list users ==
 +
use admin;
 +
db.getUsers();
 +
 
 +
== create user ==
 +
  use admin;
 +
<pre>
 +
db.createUser(
 +
  {
 +
    user: "myTester",
 +
    pwd:  passwordPrompt(),  // or cleartext password
 +
    roles: [ { role: "readWrite", db: "test" },
 +
            { role: "read", db: "reporting" } ]
 +
  }
 +
)
 +
</pre>
 +
 
 +
== add role to a user ==
 +
<pre>
 +
 
 +
db.grantRolesToUser('<username>', [
 +
  { role: "readWrite", db: "<dbname>" }
 +
], { w: "majority" , wtimeout: 4000 })
 +
 
 +
</pre>
 +
 
 +
= Performance Tuning =
  
 
  db.getProfilingStatus()
 
  db.getProfilingStatus()
Line 22: Line 64:
 
  db.setProfilingLevel(1, 10)
 
  db.setProfilingLevel(1, 10)
 
  db.getCollection('system.profile').find({})
 
  db.getCollection('system.profile').find({})
 +
 +
== profiling ==
 +
Profiling. From: https://docs.mongodb.com/manual/reference/method/db.setProfilingLevel/
 +
 +
The profiler writes all the data it collects to the system.profile collection, a capped collection in the admin database.
 +
 +
db.getProfilingStatus()
 +
# db.setProfilingLevel(level, options)
 +
db.setProfilingLevel(1, { "slowms": 500 })
 +
 +
db.enableFreeMonitoring()
 +
 +
use creek_development
 +
db.setProfilingLevel(1, { "slowms": 500 })
 +
db.getCollection('system.profile').find({}).sort({"ts": -1}).limit( 5 )
 +
 +
db.lineitems.getIndexes()
 +
 +
== view slow queries ==
 +
 +
=== In ruby: ===
 +
 +
  config.mongoid.logger      = Logger.new(Rails.root.join( 'tmp', 'mongo.log' ))
 +
  config.mongoid.logger.level = Logger::DEBUG
 +
 +
Mongoid logging can also show caller location if you enable it:
 +
 +
  Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::COMMAND) do |event|
 +
    Rails.logger.debug("Mongo Query: #{event.command}")
 +
  end
 +
 +
Use .explain on Suspicious Queries:
 +
 +
  User.where(email: "test@example.com").explain
 +
 +
=== In mongosh (old mongo): ===
 +
 +
(no need to restart mongo):
 +
 +
  use creek_staging ;
 +
  db.setProfilingLevel(1, { slowms: 100 })
 +
  db.system.profile.find().sort({ ts: -1 }).limit(5)
 +
 +
This means:
 +
 +
* 0 → profiling off
 +
* 1 → log slow queries only (recommended)
 +
* 2 → log all queries (very heavy, avoid in production)

Latest revision as of 19:02, 16 March 2026

Install

From: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-os-x/

From: https://docs.mongodb.org/manual/tutorial/install-mongodb-on-ubuntu/

From: https://docs.mongodb.com/manual/tutorial/install-mongodb-on-red-hat/


Develop

rename a field, or paste one field to another collection-wide

Methods are: updateOne, updateMany or update 

db.collection.<update method>(
    {},
    [
        {"$set": {"name": { "$concat": ["$firstName", " ", "$lastName"]}}}
    ]
)

Count Documents

db.collection.aggregate(
  [
    { $group: { _id: null, count: { $sum: 1 } } }
  ]
)

list users

use admin;
db.getUsers();

create user

 use admin;

db.createUser(
  {
    user: "myTester",
    pwd:  passwordPrompt(),   // or cleartext password
    roles: [ { role: "readWrite", db: "test" },
             { role: "read", db: "reporting" } ]
  }
)

add role to a user


db.grantRolesToUser('<username>', [
  { role: "readWrite", db: "<dbname>" }
], { w: "majority" , wtimeout: 4000 })

Performance Tuning

db.getProfilingStatus()
db.getProfilingLevel()
db.setProfilingLevel(1, 10)
db.getCollection('system.profile').find({})

profiling

Profiling. From: https://docs.mongodb.com/manual/reference/method/db.setProfilingLevel/

The profiler writes all the data it collects to the system.profile collection, a capped collection in the admin database. 

db.getProfilingStatus()
# db.setProfilingLevel(level, options)
db.setProfilingLevel(1, { "slowms": 500 })

db.enableFreeMonitoring()

use creek_development
db.setProfilingLevel(1, { "slowms": 500 })
db.getCollection('system.profile').find({}).sort({"ts": -1}).limit( 5 )

db.lineitems.getIndexes()

view slow queries

In ruby:

 config.mongoid.logger       = Logger.new(Rails.root.join( 'tmp', 'mongo.log' ))
 config.mongoid.logger.level = Logger::DEBUG

Mongoid logging can also show caller location if you enable it: 

 Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::COMMAND) do |event|
   Rails.logger.debug("Mongo Query: #{event.command}")
 end

Use .explain on Suspicious Queries: 

 User.where(email: "test@example.com").explain

In mongosh (old mongo):

(no need to restart mongo): 

 use creek_staging ;
 db.setProfilingLevel(1, { slowms: 100 })
 db.system.profile.find().sort({ ts: -1 }).limit(5)

This means:

  • 0 → profiling off
  • 1 → log slow queries only (recommended)
  • 2 → log all queries (very heavy, avoid in production)
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