Proposal: Change of pg_trigger.tg_enabled and adding pg_rewrite.ev_enabled

The experience with Slony-I has shown that
  a) different behavior of triggers and rules on a transactions origin     and a replica is essential;
  b) mucking around with the system catalog to achieve this is futile.

This would be even more catastrophic in a multimaster environment, where 
regular transaction origin and replica behavior are required on a per 
session level concurrently.

To achieve the required flexibility, we need to change the definition of 
the pg_trigger attribute tg_enabled. It currently is a boolean. I would 
like to change it into a char along with the syntax of ALTER TRIGGER. 
The value definitions of tg_enabled would be
    A   fires always    N   fires never    O   fires on transaction origin only    R   fires on replica only

Anyone preferences how to map that to ALTER TRIGGER?

A new per session GUC variable, restricted to superusers, will define if 
the session is in origin or replica mode.

Likewise the system catalog pg_rewrite is extended with an attribute 
ev_enabled. It will have the same possible values and a new command, 
ALTER RULE, will match the functionality of ALTER TRIGGER.


Jan

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