Example: MongoDB

Replica Set

• Administration:

  • A cluster name shared by all nodes: name field from replSetGetStatus.
  • A cluster-unique name for the node: name field from replSetGetStatus.
  • Version information: buildInfo.

• Clustering: mongod instances talking to each other.

• Sharding: (A shard is the entire replica set)

  • A shard ID: RS name.
  • [Optional] An indicator of when the last write operation happened (commit offset):
    • A commit offset unit (i.e, seconds, commits, …): seconds (since epoch).
    • A commit offset value (as a 64-bits integer): replSetGetStatus.

• Replication:

  • Which shards are on the node: a single shard named after the replica set.
  • For each shard, what the role on the node is: replSetGetStatus.
  • [Optional] For each non-primary shard, the replication lag:
    • The replication lag unit (i.e, seconds, commits, …): seconds.
    • The replication lag value (as a 64-bits integer): replSetGetStatus.

Sharded Cluster

• Administration:

  • A cluster name shared by all nodes: user defined in agent configuration.
  • A cluster-unique name for the node:
    • mongod: name field from replSetGetStatus.
    • mongos: user defined in agent configuration.
  • Version information: buildInfo.

• Clustering:

  • mongod instances forming the configuration Replica Set.
  • mongod instances forming shard Replica Sets.
  • mongos instances routing queries.

• Sharding:

  • A shard is …:
    • mongod: a shard is one of the Replica Sets storing the data.
    • mongos: mongos instances have no shards on them.
  • A shard ID: the shard’s RS name.
  • [Optional] An indicator of when the last write operation happened (commit offset):
    • A commit offset unit (i.e, seconds, commits, …): seconds (since epoch).
    • A commit offset value (as a 64-bits integer): replSetGetStatus.

• Replication:

  • Which shards are on the node: a single shard named as the replica set.
  • For each shard, what the role on the node is: replSetGetStatus
  • [Optional] For each non-primary shard, the replication lag:
    • The replication lag unit (i.e, seconds, commits, …): seconds.
    • The replication lag value (as a 64-bits integer): replSetGetStatus.