Replication in MongoDB

High throughput

Increase availability

Maintain copies of data like one in DR , one for reporting

Replica set members: primary , secondary

	C:\Program Files\MongoDB 2.6 Standard\bin>mongod --dbpath C:\data\rs1 --port 27017 --replset rs101 --smallfiles - oplogsize 16
			C:\Program Files\MongoDB 2.6 Standard\bin>mongod --dbpath C:\data\rs2 --port 27018 --replSet rs101 --smallfiles - oplogsize 16

C:\>mongo --port 27017

> var myconf ={_id:"rs101", members:[{_id:0,host:"localhost:27017"}]}

> myconf

{

        "_id" : "rs101",

        "members" : [

                {

                        "_id" : 0,

                        "host" : "localhost:27017"

                }

        ]

}

>

> rs.initiate(myconf)

{

        "info" : "Config now saved locally.  Should come online in about a minute.",

        "ok" : 1

}

rs101:OTHER>

rs101:PRIMARY>

rs101:PRIMARY> rs.status()

{

        "set" : "rs101",

        "date" : ISODate("2015-06-30T11:19:19Z"),

        "myState" : 1,

        "members" : [

                {

                        "_id" : 0,

                        "name" : "localhost:27017",

                        "health" : 1,

                        "state" : 1,

                        "stateStr" : "PRIMARY",

                        "uptime" : 598,

                        "optime" : Timestamp(1435663092, 1),

                        "optimeDate" : ISODate("2015-06-30T11:18:12Z"),

                        "electionTime" : Timestamp(1435663092, 2),

                        "electionDate" : ISODate("2015-06-30T11:18:12Z"),

                        "self" : true

                }

        ],

        "ok" : 1

}

rs101:PRIMARY> rs.add("localhost:27018")

{ "ok" : 1 }

rs101:PRIMARY>

rs101:PRIMARY> rs.status()

{

        "set" : "rs101",

        "date" : ISODate("2015-06-30T11:22:00Z"),

        "myState" : 1,

        "members" : [

                {

                        "_id" : 0,

                        "name" : "localhost:27017",

                        "health" : 1,

                        "state" : 1,

                        "stateStr" : "PRIMARY",

                        "uptime" : 759,

                        "optime" : Timestamp(1435663208, 1),

                        "optimeDate" : ISODate("2015-06-30T11:20:08Z"),

                        "electionTime" : Timestamp(1435663092, 2),

                        "electionDate" : ISODate("2015-06-30T11:18:12Z"),

                        "self" : true

                },

                {

                        "_id" : 1,

                        "name" : "localhost:27018",

                        "health" : 1,

                        "state" : 2,

                        "stateStr" : "SECONDARY",

                        "uptime" : 112,

                        "optime" : Timestamp(1435663208, 1),

                        "optimeDate" : ISODate("2015-06-30T11:20:08Z"),

                        "lastHeartbeat" : ISODate("2015-06-30T11:22:00Z"),

                        "lastHeartbeatRecv" : ISODate("2015-06-30T11:21:59Z"),

                        "pingMs" : 0,

                        "syncingTo" : "localhost:27017"

                }

        ],

        "ok" : 1

}

rs101:PRIMARY>

C:\>mongo --port 27018

MongoDB shell version: 2.6.5

connecting to: 127.0.0.1:27018/test

Server has startup warnings:

2015-06-30T16:42:50.272+0530 [initandlisten]

2015-06-30T16:42:50.272+0530 [initandlisten] ** NOTE: This is a 32 bit MongoDB binary.

2015-06-30T16:42:50.272+0530 [initandlisten] **       32 bit builds are limited to less than 2GB of data (or less

with --journal).

2015-06-30T16:42:50.272+0530 [initandlisten] **       Note that journaling defaults to off for 32 bit and is curr

ntly off.

2015-06-30T16:42:50.272+0530 [initandlisten] **       See http://dochub.mongodb.org/core/32bit

2015-06-30T16:42:50.288+0530 [initandlisten]

rs101:SECONDARY>

rs101:PRIMARY> show dbs

admin  (empty)

local  0.063GB

rs101:PRIMARY> use mydb

switched to db mydb

rs101:PRIMARY> db.createCollection("rstable")

{ "ok" : 1 }

rs101:PRIMARY>

rs101:SECONDARY> show dbs

admin  (empty)

local  0.063GB

mydb   0.031GB

rs101:SECONDARY> show collections

2015-06-30T16:57:15.761+0530 error: { "$err" : "not master and slaveOk=false", "code" : 13435 } at src/mongo/shel

/query.js:131

rs101:SECONDARY>

Mongo doesn’t allow read /write from secondary by default