what does -r cmd line option do ?

Community Support
1

http://code.kx.com/wiki/Reference/Cmdline

-r :H:P[:user[:password]]
replicate from :host:port

But is there a practical use case you can define ?
2

-r is for Replication. It’s a way of mirroring the primary server state and can be used for something like creating a backup for  primary server or to reduce load from primary server.

more details on implementation :

http://code.kx.com/wiki/Cookbook/Logging#Replication

http://www.timestored.com/kdb-guides/kdb-command-line-options#kdb-logging-replication