Binlog server: Useful information to provide via maxinfo

The binlog router provides several metrics via the output of maxadmin show services.
These need to be parsed and processed and are not in a very useful format.

It would be convenient to be able to access this status information using the new maxinfo infrastructure, probably in several "tables". The following values below imply having a single master whereas in reality MaxScale could have more than one configured binlog router. For now I'm only assuming the case of having a single active connection.

The type of thing that I would like to see are:

• number of connected clients via the SQL interface
• number of connected slaves via the SQL interface
• connected_to_master (values: 0 / 1) to indicate if I'm connected to the master
• number of packets received from the master
• number of connections to the master
• number of disconnections from the master
• number of events received from the master
• number of transactions received from the master (transaction safety functionality)
• number of heartbeats events received from the master
• connection time to the master (in seconds)

For the slaves we basically want the same values. MaxScale can not at the moment do aggregations so you probably want to create a table with the current connected slaves which looks like this:

server-id
hostname
slave-uuid
slave_host_post
username
state
binlog_file
binlog_pos
num_requests
num_events_sent
num_bytes_sent
num_bursts_sent
num_transitions_to_follow_mode
num_flow_control
num_up_to_date
num_drained_cbs
num_failed_reads
last_binlog_event_timestamp
seconds_behind_master
slave_mode

Given I can't do SELECT sum(...), Sum(...) from ... GROUP BY ... then having a sum_all_slaves table with the sum of the above metrics for all active slaves, would probably be good. Don't forget to add an additional count_slaves column so that we know for how many slaves the values are being shown.

Providing this sort of output via some maxinfo structures would be good.