MongoDB - Replication -Part I

I will be running Mongod instance in windows environment. I am planning to create one primary and 2 secondary instances.
First, I have created 3 folders in C:\
c:\MongoRepl\1
c:\MongoRepl\2
c:\MongoRepl\3

I will be using port no 27007 (primary) ,27008 ,27009. I have made sure these ports are allowed incoming/outgoing in firewall.

Now, I will create a standalone mongod instance first. Then, create a database on the instance.

mongod --dbpath c:\MongoRepl\1 --port 27007 --smallfiles --oplogSize 50

open another terminal and connect to Mongod shell and import replication database

mongo --port 27007 --shell replication.js

Now, Cloed the mongod shell. Restarted Mongod instance as a replica.

mongod --replSet Mya --dbpath c:\MongoRepl\1 --port 27007 --smallfiles --oplogSize 50

You will set EMPTYConfig error.

Next, we will start two other mongod instances (secondary), we will join them to replicaset Mya

mongod --replSet Mya --dbpath c:\MongoRepl\2 --port 27008 --smallfiles --oplogSize 50

mongod --replSet Mya --dbpath c:\MongoRepl\3 --port 27009 --smallfiles --oplogSize 50

Now, we will initiate a replica from mongo us initiate command.

rs.initiate()
rs.status()

create a configuration

cfg={
_id:"Mya",
members:[
{_id:0,host:"machinename:27007"},
{_id:1,host:"machinename:27008"},
{_id:2,host:"machinename:27009"},
]
}

Initiate Replica

rs.initiate(cfg)

Check replica status on primary 

rs.status()

Open termainal and start mongo

mongo --port 27008
mongo --port 27009

Read from secondary

I need to run rs.slaveOk() to read from secondary

rs.slaveOk()

Write to Primary

for(var i=0; i< 50000;i++){db.foo.insert({_id:i});sleep(i);}

While for statement is running, check on secondary rowcount

db.foo.count()

FailOver to Secondary

Run the command in Primary

rs.stepDown()

Now new primary is 27008

Now we will close Mongod instance on 27007.

rs.status()
27007 is unreachable since we shut down 27007

Reconfigure

On new primary replica. run config and rs.reconfig(cfg)

cfg={
_id:"Mya",
members:[
{_id:1,host:"machinename:27008"},
{_id:2,host:"machinename:27009"},
]
}

rs.reconfig(cfg)

Now, we have even number node.

Replica set information are stored in local db

use local
db.system.replset.find().pretty()

MongoDB - Dynamic_Schema/MongoImport/Cursor/Queries/Sorting

Dynamic Schema
-Polymorphism

Schemaless / Polymorphism

--add new fields easily to schema

Things

{Shape:"Rect",x:3,y:4,Area:12}

{Shape:"Circle",radius:1,Area:3.14}

Mongo Import

Open another command prompt

mongoimport.exe can import 3 types of files CSV,TSV,JSON

mongoimport --db databasename --collection tablename < filename

mongoimport --stopOnError

mongoimport --db pcat --collection products < products.json

Mongo Shell Queries

--show recordcount

db.collection.count()

--show all rows

db.collection.find()

--Show only name column

db.collection.find({},{name:1})

--show all rows nicely

db.collection.find().toArray()

--show only 10 rows nicely 

db.collection.find({}).limit(10).toArray()

--Show only 1 row

db.collection.findOne()

db.collection.find({}).limit(1)

--Skip first 2 and give next 4

db.collection.find({}).limit(4).Skip(2)   -

--Turn off Id

db.collection.find({},{name:1,_id:0})

--Get Name and Brand

db.collection.find({},{name:1,brand:1})

--All fields and 1 row

db.collection.find({}).limit(1)

--if the output is not too big

db.collection.find({}).limit(3).toArray()

--query price = 12.5

db.collection.find({price:12.5})

db.collection.find({price:12.5}).toArray()

db.collection.find({},{price:1})

--Object id is bson type, not string

-- Get one document

db.collection.findOne({"_id": ObjectId("ddadfa5464565fgafaddadffadfadfgffd")})

db.collection.find({price:200},{name:1,price:1})

--greater than

db.collection.find({price: {$gte:200}},{name:1,price:1})

$Operators

Querying

$gte

$gt

$lt

$lte

$or

$not

$nin

$in

$type

$exists

Updating

$inc

$set

$addToSet

--greater than and expression

db.collection.find({price: {$gte:200},available:true},{name:1,price:1,available:1})

--find ac3 is in array

db.collection.find({for : "ac3"}) 

Reaching into Nested Documents

dot notation

find({"x.a":1})

Quiz

Add caption

db.collection.find({for:"ac9",Type:"case"}).toArray()

Sorting

db.collection.find(_).sort(fieldname:direction)

db.collection.find({},{name:1,price:1}).sort({price:1})

-- null is less than number

--sort rows only with price

db.collection.find({price:{$exists:true}},{name:1,price:1}).sort({price:1})

db.collection.find({price:{$exists:true}},{name:1,price:1}).sort({price:-1})

Multiple Sort keys

db.collection.find().sort({lastname:1,firstname:1})

--SQL order by lastname,firstname

Cursors (different from other database)

db.test.find()

type it for more

db.test.find().skip(20).limit(5)

--skip is expensive, 20 is fine if 5000 is expensive.

--sort and skip is done at the server

Example

var cursor = db.test.find()

cursor.hasNext()

MongoDB - JSON/BSON/Documents

MongoDB - Lesson 1 

These are my notes from MongoDB university free DBA class.

MongoDB works on concept of collection and document.

MySQL   |   MongoDB  
Database = Database
Table = Collection
Row = Document
Column = Field
Table Join = Embedded Documents
Primary Key = Default key _id provide by mongodb itself

MongoDB language is based on JSON Language. No Join / No complex transaction.

JSON

Example : Document/Row
{ _id :"A11",
x :"1",
y:"2",
z:{a,b} --embedding
}

Find id = A11

Example: query

db.collection.find({_id: "A11"})

JSON Types (Java Script Object Notation)

- Pure data exchange format
- Document-Oriented

Quiz : How many data types in Json ?

Ans : 6

1. Strings
2. Numbers
3. Booleans(True\False)
4. Null
5. Arrays
6. Objects/Documents

Left hand side - Only String is a valid type

Quiz

Ans:

Person
{"name" : "John",
  "Age" : 25,
 "Address" :
  {"city" : "New York",
     "PostalCode" : 10021
 }
"Phone" :
{"Home": "212-555-1234",
"Mobile": "646-555-1234"
}
}

Binary JSON

Fast Scannability
Data types

1. Binary Data
2. Object ID

BSON Format

-- Mongodb driver

integer = 32 bit (4 bytes)

BSON and Applications

Starting MONGODB - NoSQL

I heard about MongoDB from a friend and wanted to try out open source database.

Installing Mongo DB

http://docs.mongodb.org/manual/tutorial/install-mongodb-on-windows/

I am installing MongoDB on windows 7. I have downloaded windows version from Mogodb website and unpacked msi.

• move bin folder to C:\MogoDB\
• create a directory for data - c:\data\db
• Setting data path
• c:\mongodb\bin\mongod.exe --dbpath c:\data\db

Starting MongoDB service

Open a command prompt

C:\MongoDB\Bin\Mongod.exe

Waiting for connections on port 27017 means MongoDB service is successfully started.

Open another command Prompt to connect to Mongo Database

Type

C:\mongodb\bin\Mongo.exe

You will see the error that cannot find the file mongorc.js

So you tell the shell to ignore looking for .mongorc.js

C:\MongoDB\Bin\Mongo.exe --norc --shell

Now you are successfully connected to database.

type 

db

it will return test, connecting to test database

use mydb

show collections

Generate test data in a loop

Read inserted data

It was fun to play with MongoDB. More posts will be coming soon...