## Collections on Replica Set Members 

local.system. replset 

local.system.replset (page 654) holds the replica set’s configuration object as its single document. To view the object’s configuration information, issue rs.conf() from the mongo shell. You can also query this collection directly. 

local.oplog. rs 

local.oplog.rs (page 654) is the capped collection that holds the oplog . You set its size at creation using the oplogSizeMB setting. To resize the oplog after replica set initiation, use the Change the Size of the Oplog (page 628) procedure. For additional information, see the Oplog Size (page 593) section. 

local.replset. minvalid 

This contains an object used internally by replica sets to track replication status. 

local. slaves 

Removed in version 3.0: Replica set members no longer mirror replication status of the set to the local.slaves (page 654) collection. Use rs.status() instead. 

## Collections used in Master/Slave Replication 

In master / slave replication, the local database contains the following collections: 

• On the master: 

local.oplog. $main 

local. slaves 

This is the oplog for the master-slave configuration. 

Removed in version 3.0: MongoDB no longer stores information about each slave in the local.slaves (page 654) collection. Use db.serverStatus( { repl: 1 } ) instead. 

• On each slave: 

local. sources 

## Replica Set Member States 

Each member of a replica set has a state that reflects its disposition within the set. 

This contains information about the slave’s master server. 

