Replication Methods - MongoDB Shell

In MongoDB, replication is the process of synchronizing data across multiple servers. The replication process is essential for ensuring high availability and fault tolerance in a distributed system.

In this page, we will discuss the different replication methods available in MongoDB using the MongoDB shell.

Syntax

The process of configuring replication in MongoDB typically involves the following steps:

1. Creating a replica set
2. Adding replica set members
3. Configuring replica set parameters

To configure a replica set in MongoDB, you can use the following commands in the MongoDB shell:

rs.initiate()
rs.add("hostname:port")
rs.conf()

Example

Here's an example of configuring a replica set with three members in the MongoDB shell:

1. Start three MongoDB instances on different ports.

mongod --port 27017 --dbpath /data/rs1 --replSet rs0
mongod --port 27018 --dbpath /data/rs2 --replSet rs0
mongod --port 27019 --dbpath /data/rs3 --replSet rs0

2. Connect to one of the instances using the MongoDB shell.

mongo --port 27017

3. Initialize the replica set.

rs.initiate()

4. Add the other two members to the replica set.

rs.add("localhost:27018")
rs.add("localhost:27019")

5. View the replica set configuration.

rs.conf()

Output

The rs.conf() command will output the current replica set configuration in the shell.

{
    "_id" : "rs0",
    "version" : 1,
    "protocolVersion" : NumberLong(1),
    "members" : [
        {
            "_id" : 0,
            "host" : "localhost:27017",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1.0,
            "tags" : {},
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 1,
            "host" : "localhost:27018",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1.0,
            "tags" : {},
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        },
        {
            "_id" : 2,
            "host" : "localhost:27019",
            "arbiterOnly" : false,
            "buildIndexes" : true,
            "hidden" : false,
            "priority" : 1.0,
            "tags" : {},
            "slaveDelay" : NumberLong(0),
            "votes" : 1
        }
    ],
    "settings" : {
        "chainingAllowed" : true,
        "heartbeatIntervalMillis" : 2000,
        "heartbeatTimeoutSecs" : 10,
        "electionTimeoutMillis" : 10000,
        "catchUpTimeoutMillis" : -1,
        "catchUpTakeoverDelayMillis" : 30000,
        "getLastErrorModes" : {},
        "getLastErrorDefaults" : {
            "w" : 1,
            "wtimeout" : 0
        },
        "replicaSetId" : ObjectId("5fec300e4e66935607ef11b3")
    }
}

Explanation

In the example above, we created a replica set with three members, each running on a different port. We then connected to one of the instances using the MongoDB shell and initialized the replica set using the rs.initiate() command. We then added the other two members to the replica set using the rs.add() command. Finally, we viewed the replica set configuration using the rs.conf() command.

Use

Replication is important in MongoDB because it provides high availability and fault tolerance for your data. By configuring multiple replica set members, you can ensure that your data is always available even if a primary member fails.

Important Points

• Replication is the process of synchronizing data across multiple servers.
• Replication is essential for ensuring high availability and fault tolerance in a distributed system.
• MongoDB replica sets can have multiple members running on different servers.
• Replication can be configured using the MongoDB shell.

Summary

In this page, we discussed the different replication methods available in MongoDB using the MongoDB shell. We covered the syntax, example, output, explanation, use, and important points of MongoDB replication. By configuring replication, you can ensure high availability and fault tolerance for your data, providing a more reliable and robust distributed system.