Re: including backend ID in relpath of temp rels - updated patch

On Fri, Aug 6, 2010 at 3:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> This patch only directly addresses the issue of cleaning up the
>> storage, so there are still the catalog entries to worry about.  But
>> it doesn't seem impossible to think about building on this approach to
>> eventually handle that part of the problem better, too.  I haven't
>> thought too much about what that would look like, but I think it could
>> be done.
>
> Perhaps run through pg_class after restart and flush anything marked
> relistemp?

The trouble is that you have to bind to a database before you can run
through pg_class, and the postmaster doesn't. Of course, if it could
attach to a database and then detach again, this might be feasible,
although perhaps still a bit overly complex for the postmaster, but in
any event it doesn't. We seem to already have a mechanism in place
where a backend that creates a temprel nukes any pre-existing temprel
schema for its own backend, but of course that's not fool-proof.

> Although the ideal solution, probably, would be for temp
> tables to not have persistent catalog entries in the first place.

I've been thinking about that, but it's a bit challenging to imagine
how it could work. It's not just the pg_class entries you have to
think about, but also pg_attrdef, pg_attribute, pg_constraint,
pg_description, pg_index, pg_rewrite, and pg_trigger. An even
stickier problem is that we have lots of places in the backend code
that refer to objects by OID. We'd either need to change all of that
code (which seems like a non-starter) or somehow guarantee that the
OIDs assigned to any given backend's private objects would be
different from those assigned to any public object (which I also don't
see how to do).

--
Robert Haas
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