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Deploy Sharded Cluster using Hashed Sharding

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Overview

Hashed shard keys use a hashed index of a single field as the shard key to partition data across your sharded cluster.

Hashed sharding provides more even data distribution across the sharded cluster at the cost of reducing Query Isolation. Post-hash, documents with “close” shard key values are unlikely to be on the same chunk or shard - the mongos is more likely to perform 广播发送的操作 to fulfill a given query.

If you already have a sharded cluster deployed, skip to Shard a Collection using Hashed Sharding.

CloudManager and OpsManager

If you are currently using or are planning to use Cloud Manager or Ops Manager, consider using their built-in features for deploying a sharded cluster.

See Deploy a Sharded Cluster in the Cloud Manager manual or in the Ops Manager manual.

Considerations

Operating System

This tutorial uses the mongod and mongos programs. Windows users should use the mongod.exe and mongos.exe programs instead.

Security

This tutorial does not include the required steps for configuring Internal Authentication or Role-Based Access Control. See Deploy Sharded Cluster with Keyfile Access Control for a tutorial on deploying a sharded cluster with a keyfile.

In production environments, sharded clusters should employ at minimum x.509 security for internal authentication and client access.

For details on using x.509 for internal authentication, see Use x.509 Certificate for Membership Authentication.

For details on using x.509 for client authentication, see Use x.509 Certificates to Authenticate Clients.

注解

Enabling internal authentication also enables Role-Based Access Control.

Deploy Sharded Cluster with Hashed Sharding

The following procedures involve creating a new sharded cluster that consists of a mongos, the config servers, and two shards.

Create the Config Server Replica Set

The following steps deploys a config server replica set.

For a production deployment, deploys a config server replica set with at least three members. For testing purposes, you can create a single-member replica set.

1

Start each member of the config server replica set.

Start each mongod in the config server replica set.

You can specify the mongod settings either via a configuration file or the command line.

Configuration File

If using a configuration file, set sharding.clusterRole to configsvr, and replication.replSetName to the desired name of the config server replica set.

sharding:
  clusterRole: configsvr
replication:
  replSetName: <setname>

Include additional settings as appropriate to your deployment. For more information on the configuration file, see configuration options.

Start the mongod specifying the --config option and the path to the configuration file.

mongod --config <path-to-config-file>

Command Line

If using the command line parameters, start the mongod with the --configsvr, and --replSet parameters.

mongod --configsvr --replSet <setname> --dbpath <path>

Include additional settings as appropriate to your deployment. For more information on startup parameters, see the mongod reference page.

2

Connect to one of the config servers.

Connect a mongo shell to one of the config server members.

mongo --host <hostname> --port <port>
3

The rs.initiate() method initiates the replica set and can take an optional replica set configuration document. In the replica set configuration document, include:

  • The _id. The _id must match the --replSet parameter passed to the mongod.
  • The members field. The members field is an array and requires a document per each member of the replica set.
  • The configsvr field. The configsvr field must be set to true for the config server replica set.

See Replica Set Configuration for more information on replica set configuration documents.

Initiate the replica set using the rs.initiate() method and a configuration document:

rs.initiate(
  {
    _id: "<replSetName>",
    configsvr: true,
    members: [
      { _id : 0, host : "cfg1.example.net:27017" },
      { _id : 1, host : "cfg2.example.net:27017" },
      { _id : 2, host : "cfg3.example.net:27017" }
    ]
  }
)

Once the config server replica set (CSRS) is initiated and up, proceed to creating the shard replica sets.

Create the Shard Replica Sets

For a production deployment, use a replica set with at least three members. For testing purposes, you can create a single-member replica set.

1

Start each member of the shard replica set.

Start each mongod in the replica set using either a configuration file or the command line.

Configuration File

If using a configuration file, set the replication.replSetName to the desired name of the replica set, and the sharding.clusterRole option to shardsvr.

sharding:
  clusterRole: shardsvr
replication:
  replSetName: <replSetName>

Include any other options as appropriate for your deployment. See 配置文件选项 for settings available.

Start the mongod specifying the --config option and the path to the configuration file.

mongod --config <path-to-config-file>

Command Line

If using the command line option, when starting the component, specify the replSet, and --shardsvr parameters, as in the following example:

mongod --shardsvr --replSet <replSetname>

Include any other options as appropriate for your deployment.

For more information on startup parameters, see the mongod reference page.

Include additional settings as appropriate to your deployment.

2

Connect to a member of the shard replica set.

Connect a mongo shell to one of the replica set members.

mongo --host <hostname> --port <port>
3

Initiate the replica set.

The rs.initiate() method initiates the replica set and can take an optional replica set configuration document.

In the replica set configuration document, include:

  • The _id field. The _id must match the --replSet parameter passed to the mongod.
  • The members field. The members field is an array and requires a document per each member of the replica set.

See Replica Set Configuration for more information on replica set configuration documents.

The following example initates a three member replica set.

rs.initiate(
  {
    _id : <replicaSetName>,
    members: [
      { _id : 0, host : "s1-mongo1.example.net:27017" },
      { _id : 1, host : "s1-mongo2.example.net:27017" },
      { _id : 2, host : "s1-mongo3.example.net:27017" }
    ]
  }
)

rs.initiate() triggers an election and elects one of the members to be the primary.

Connect to the primary before continuing. Use rs.status() to locate the primary member.

Connect a mongos to the Sharded Cluster

1

Connect a mongos to the cluster

Start a mongos specifying using either a configuration file or a command line parameter.

Configuration File

If using a configuration file, set the sharding.configDB to the config server replica set name and at least one member of the replica set in <replSetName>/<host:port> format.

sharding:
  configDB: <configReplSetName>/cfg1.example.net:27017,cfg2.example.net:27017,...

Start the mongos specifying the --config option and the path to the configuration file.

mongos --config <path-to-config>

For more information on the configuration file, see configuration options.

Command Line

If using command line parameters start the mongos and specify the --configdb parameter.

mongos --configdb <configReplSetName>/cfg1.example.net:27017,cfg2.example.net:27017,...

Include any other options as appropriate for your deployment.

2

Connect to the mongos.

Connect a mongo shell to the mongos.

mongo --host <hostname> --port <port>

Add Shards to the Cluster

Use the sh.addShard() method to add each shard to the cluster. If the shard is a replica set, specify the name of the replica set and specify a member of the set. In production deployments, all shards should be replica sets.

The following operation adds a single shard replica set to the cluster:

sh.addShard( "<replSetName>/s1-mongo1.example.net:27017")

The following operation is an example of adding a standalone mongod shard to the cluster:

sh.addShard( "s1-mongo1.example.net:27017")

Repeat these steps until the cluster includes all shards.

Enable Sharding for a Database

To proceed, you must be connected to a mongos associated to the target sharded cluster.

Enabling sharding on a database makes it possible to shard collections within a database. Use the sh.enableSharding() method to enable sharding on the target database.

sh.enableSharding("<database>")

Shard a Collection using Hashed Sharding

To proceed, you must be connected to a mongos associated to the target sharded cluster.

To shard a collection, use the sh.shardCollection() method. You must specify the full namespace of the collection and a document containing the shard key. The database must have sharding enabled.

Your selection of shard key affects the efficiency of sharding, as well as your ability to take advantage of certain sharding features such as zones. See the selection considerations listed in the Hashed Sharding Shard Key.

If the collection already contains data, you must create a Hashed Indexes on the shard key using the db.collection.createIndex() method before using shardCollection().

If the collection is empty, MongoDB creates the index as part of sh.shardCollection().

The following operation shards the target collection using the hashed sharding strategy.

sh.shardCollection("<database>.<collection>", { <key> : <direction> } )

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