Re: [Patch] Temporary tables that do not bloat pg_catalog (a.k.a fast temp tables)

Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> But there are some patterns used with work with temp tables,that should not
> working, and we would to decide if we prepare workaround or not.

> -- problematic pattern (old code)
> IF NOT EXISTS(SELECT * FROM pg_class WHERE ....) THEN
> CREATE TEMP TABLE xxx()
> ELSE
> TRUNCATE TABLE xxx;
> END IF;

> -- modern patter (new code)
> BEGIN
> TRUNCATE TABLE xxx;
> EXCEPTION WHEN ..... THEN
> CREATE TEMP TABLE(...)
> END;

If the former stops working, that's a sufficient reason to reject the
patch: it hasn't been thought through carefully enough. The key reason
why I don't think that's negotiable is that if there aren't (apparently)
catalog entries corresponding to the temp tables, that will almost
certainly break many things in the backend and third-party extensions,
not only user code patterns like this one. We'd constantly be fielding
bug reports that "feature X doesn't work with temp tables anymore".

In short, I think that the way to make something like this work is to
figure out how to have "virtual" catalog rows describing a temp table.
Or maybe to partition the catalogs so that vacuuming away temp-table
rows is easier/cheaper than today.

regards, tom lane