Chaining commands to siblings (for when warming up_

[powerdns]

Chaining commands to siblings (for when warming up_

[neilcook]

Alternatively when booting, synchronise statsdb old time windows (except current) (MRU first) with a wforce sibling that already has the stats (assuming there is one).

[neilcook]

One model:

• Set a "min time sibling must be up" before a newly started server will pull old stats from it
• Set a list of "catchup" servers that will be used for pulling stats
  • Contact each configured catchup server and see if it has been up long enough
• If I find any catchup servers which have been up long enough:
  • Set status to "warming up" - this needs a new ping command response (see #48)
  • Contacts a catchup server that has been up long enough, and tell it to send us all old stats (only old time windows not the current time window?)
  • Keep going until we have all the old time windows and all the keys (we know this because we set a callback for the catchup server to tell us when its done)
• If no catchup servers available which exceed the minimum uptime, then set status to "ready"

[neilcook]

Also consider making the standard replication work over TCP as part of this work

[neilcook]

Merged #202