On Thu, Jul 10, 2014 at 11:11:19PM +0200, Andres Freund wrote: > On 2014-07-10 16:33:40 -0400, Bruce Momjian wrote: > > On Thu, Jul 10, 2014 at 10:46:30AM -0400, Robert Haas wrote: > > > > Agreed. I am now thinking we could harness the code that already exists > > > > to optionally add a TOAST table as part of ALTER TABLE ADD COLUMN. We > > > > would just need an entry point to call it from pg_upgrade, either via an > > > > SQL command that checks (and hopefully doesn't do anything else), or a C > > > > function that does it, e.g. VACUUM would be trivial to run on every > > > > database, but I don't think it tests that; is _could_ in binary_upgrade > > > > mode. However, the idea of having a C function plug into the guts of > > > > the server and call internal functions makes me uncomforable. > > > > > > Well, pg_upgrade_support's charter is basically to provide access to > > > the guts of the server in ways we wouldn't normally allow; all that > > > next-OID stuff is basically exactly that. So I don't think this is > > > such a big deal. It needs to be properly commented, of course. > > > > If you look at how oid assignment is handled, it is done in a very > > surgical way, i.e. pg_upgrade_support sets a global variable, and the > > variable triggers different behavior in a CREATE command. This change > > would be far more invasive than that. > > Meh. It's only somewhat surgical because there's pg_upgrade specific > code sprinkled in the backend at strategic places. That's the contrary > of a clear abstraction barrier. And arguably a function call from a SQL > C function has a much clearer abstraction barrier.
Well, we are going to need to call internal C functions, often bypassing their typical call sites and the assumption about locking, etc. Perhaps this could be done from a plpgsql function. We could add and drop a dummy column to force TOAST table creation --- we would then only need a way to detect if a function _needs_ a TOAST table, which was skipped in binary upgrade mode previously. That might be a minimalistic approach. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers