Re: BUG #3692: Conflicting create table statements throw unexpected error

In response to Tom Lane <tgl@sss.pgh.pa.us>:

> "Bill Moran" <wmoran@collaborativefusion.com> writes:
> > Issuing a statement like:
> > CREATE TABLE table2 AS SELECT * FROM table1;
> > simultaneously in two separate sessions should result in an error like
> > "ERROR:  relation "table2" already exists" (in one or the other of the
> > sessions, depending on the exact timing of things).
>
> This isn't really fixable, or at least the cure would be worse than the
> disease.  The "already exists" message is just a pre-check and it cannot
> detect an uncommitted concurrent attempt to insert the same table name.
> The place where the rubber really meets the road is during unique index
> insertion.  We might be able to fix things so that you get a unique
> index complaint about pg_class.relname instead of pg_type, but that
> would be about it.

I figured it was something along those lines, otherwise it would have
already been "fixed".

I haven't had time to look at the code, so I'm speaking from a position
of ignorance, but would it be terribly difficult to catch the unique
constraint error, then re-run the pre-check to determine if it's
occurring as a result of trying to create an existing table, and
translate the error to a friendlier one before reporting to the client?

That doesn't seem unreasonable to me, but (as I already admitted) I
haven't looked at the code yet ...

--
Bill Moran
Collaborative Fusion Inc.
http://people.collaborativefusion.com/~wmoran/

wmoran@collaborativefusion.com
Phone: 412-422-3463x4023