User interaction with the balancer could be improved.

Currently, to disable the balancer, users have to $set

{stopped: true}

in the balancer document. This is error-prone (it'd be easy to misspell "stopped', etc.) and there's no feedback.

I propose a couple of commands for changing the balancer's state and getting the balancer's status.

For example:

db.runCommand(

{balancerstatus: 1}

)
Returns:

{ state: 1,
msg: "Balancing round"
ops: [
describe what's scheduled for this round / what's currently happening
]
}

db.runCommand(

{disablebalancer: 1}

)

This prints a message indicating current balancer state and blocks if balancer is in the middle of something.

db.runCommand(

{enablebalancer: 1}

)

Re-enables balancing.