Bug #173 is about the notion of extending Slonik to allow one to
ask a Slonik script to error out upon running into particular
conditions.

These "ABORT" statements could be used to guard a script; if it runs
into unacceptable pre-conditions, it may terminate before it does any
damage to the cluster.

I suggest the following, as starting points:

- Behind by...
   - >= 5 events
   - >= 30 seconds

  ABORT IF BEHIND ( PROVIDER = 1, RECEIVER = 3, SECONDS = 30, comment = 'Behind by 30 seconds', return=1);
  ABORT IF BEHIND ( PROVIDER = 1, RECEIVER = 3, EVENT = 5, comment= 'Behind by 5 events', return=2);

Other Health Criteria
- Is node there?
- Is replication set there?
- Is subscription active?
- Run SQL, fail if ERROR

  ABORT IF NODE ABSENT ( EVENT NODE = 1, ID = 3, comment = 'Node 3 missing according to node 1',return=3);
  ABORT IF SET ABSENT ( EVENT NODE = 1, ID = 3, comment = 'Set 3 missing according to node 1',return=4);
  ABORT IF SET NOT SUBSCRIBED ( EVENT NODE = 1, ID = 3, comment = 'Set 3 not subscribed by node 1', return=5 );
  ABORT IF SCRIPT ERROR ( EVENT NODE = 1, script = '/tmp/myscript.sql',return=6 );

-- 
http://linuxfinances.info/info/slony.html
"If you want to travel around the world and be invited to speak at a
lot of different places, just write a Unix operating system."
-- Linus Torvalds