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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