changing primary key col(s) with minimal impact

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I have a need to provide a way to change a table's primary key
columns, in the possible presence of foreign keys, and with concurrent
use (as much as possible).

The best way I have come up with is roughly:
a. create the to-be-new-pk index concurrently
b. "demote" the old pk to be a unique constraint
c. alter table add constraint new pk using existing index

Step b. involves (in one transaction):
- --------------------------------------
* update pg_class row for the table
relhaspkey false
* update pg_constraint row for the original pk
contype = 'u'
conname = 'some_new_name'
* update pg_index row for the original pk index
indisprimary = false
* alter index original pk rename to some_new_name
- --------------------------------------
I have tested this (minimally) and as far as I can tell it works.

Questions:
1) any major holes in this approach?
2) any better ideas?
3) should we consider an ALTER TABLE ALTER CONSTRAINT command
(or some such) to allow demotion of a PRIMARY KEY to a UNIQUE
constraint?

Thanks for any thoughts/comments.

Joe

- --
Joe Conway
credativ LLC: http://www.credativ.us
Linux, PostgreSQL, and general Open Source
Training, Service, Consulting, & 24x7 Support
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