Host types in Yandex StoreDoc

Yandex StoreDoc has these four host types: MONGOD, MONGOINFRA, MONGOCFG, and MONGOS. Each host type has a role and functions of its own in the cluster. The type and number of hosts in a Yandex StoreDoc cluster depend on what sharding type you select.

Roles and functions of different host typesRoles and functions of different host types

• MONGOD: Data storage and query processing hosts. These hosts are present in both sharded and non-sharded clusters.

  Primary functions of MONGOD hosts:

  • Read and write request processing.
  • User data storage.
  • Data replication.
  • Ensuring data consistency.

• MONGOCFG: Sharding configuration hosts. These hosts are present only in clusters with advanced sharding.

  Primary functions of MONGOCFG hosts:

  • Storing and updating sharding metadata on changes in the shard configuration.
  • Providing MONGOS hosts with up-to-date information about chunks and shards.
  • Coordinating chunk migration between shards.

• MONGOS: Router hosts. These hosts are present only in clusters with advanced sharding.

  Primary functions of MONGOS hosts:

  • Accepting client connections.
  • Routing queries to shards.
  • Processing of query or subquery results.
  • Delivery of final output to the client.

• MONGOINFRA: Infrastructure hosts. This host type combines the MONGOS and MONGOCFG roles. MONGOINFRA hosts are present only in clusters with standard sharding.

  Primary functions of MONGOINFRA hosts:

  • Accepting client connections.
  • Routing queries to shards.
  • Storing and updating sharding metadata on changes in the shard configuration.
  • Coordinating chunk migration between shards.
  • Processing of query or subquery results.
  • Delivery of final output to the client.

Cluster composition depending on sharding typeCluster composition depending on sharding type

The number of hosts of various types in an Yandex StoreDoc cluster depends on sharding type:

A non-sharded cluster consists exclusively of MONGOD hosts that process all client requests. Query routing is managed by the Yandex StoreDoc client.

A standard-sharded cluster consists of MONGOD and MONGOINFRA hosts.
Client requests addressed to the cluster are processed as follows:

1. The Yandex StoreDoc client connects to all MONGOINFRA hosts and sends the request to one of them.
2. The MONGOINFRA host analyzes the request and figures out what shards are affected by it.
3. The MONGOINFRA host forwards the request or the group of subrequests to relevant MONGOD hosts.
4. MONGOD hosts execute the request or subrequests.
5. The MONGOINFRA host processes the result of the request or subrequests and returns the final result to the client.

A cluster with advanced sharding consists of MONGOD, MONGOS, and MONGOCFG hosts.
Client requests addressed to the cluster are processed as follows:

1. The Yandex StoreDoc client connects to all MONGOS hosts and sends the request to one of them.
2. The MONGOS host analyzes the request and uses metadata from MONGOCFG hosts to figure out what shards are affected by it.
3. The MONGOS host forwards the request or the group of subrequests to relevant MONGOD hosts.
4. MONGOD hosts execute the request or subrequests.
5. The MONGOS host processes the result of the request or subrequests and returns the final result to the client.