MongoDB Documentation, Release 3.0.4 config. locks The config (page 738) database is internal: applications and administrators should not modify or depend upon its content in the course of normal operation. The locks (page 740) collection stores a distributed lock. This ensures that only one mongos instance can perform administrative tasks on the cluster at once. The mongos acting as balancer takes a lock by inserting a document resembling the following into the locks collection. If a mongos holds the balancer lock, the state field has a value of 2 , which means that balancer is active. The when field indicates when the balancer began the current operation. Changed in version 2.0: The value of the state field was 1 before MongoDB 2.0. config. mongos The config (page 738) database is internal: applications and administrators should not modify or depend upon its content in the course of normal operation. The mongos (page 741) collection stores a document for each mongos instance affiliated with the cluster. mongos instances send pings to all members of the cluster every 30 seconds so the cluster can verify that the mongos is active. The ping field shows the time of the last ping, while the up field reports the uptime of the mongos as of the last ping. The cluster maintains this collection for reporting purposes. The following document shows the status of the mongos running on example.com:30000 . config. settings The config (page 738) database is internal: applications and administrators should not modify or depend upon its content in the course of normal operation. The settings (page 741) collection holds the following sharding configuration settings: The following is an example settings collection: •Chunk size. To change chunk size, see Modify Chunk Size in a Sharded Cluster (page 727). •Balancer status. To change status, see Disable the Balancer (page 717). 741 10.4. Sharding Reference Internal MongoDB Metadata Internal MongoDB Metadata { "_id" : "balancer", "process" : "example.net:40000:1350402818:16807", "state" : 2, "ts" : ObjectId("507daeedf40e1879df62e5f3"), "when" : ISODate("2012-10-16T19:01:01.593Z"), "who" : "example.net:40000:1350402818:16807:Balancer:282475249", "why" : "doing balance round" } Internal MongoDB Metadata { "_id" : "example.com:30000", "ping" : ISODate("2012-10-12T17:08:13.538Z"), "up" :