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

On Tue, Aug 23, 2016 at 7:25 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>>> Could someone please explain how the unlogged tables are supposed to fix
>>> the
>>> catalog bloat problem, as stated in the initial patch submission? We'd
>>> still
>>> need to insert/delete the catalog rows when creating/dropping the
>>> temporary
>>> tables, causing the bloat. Or is there something I'm missing?
>>
>>
>> Wouldn't more aggressive vacuuming of catalog tables fix the bloat?
>>
>> Perhaps reserving a worker or N to run only on catalog schemas?
>>
>> That'd be far simpler.
>
>
> Maybe, although IIRC the issues with catalog bloat were due to a combination
> of long queries and many temporary tables being created/dropped. In that
> case simply ramping up autovacuum (or even having a dedicated workers for
> catalogs) would not realy help due to the xmin horizon being blocked by the
> long-running queries.
>
> Maybe it's entirely crazy idea due to the wine I drank at the dinner, but
> couldn't we vacuum the temporary table records differently? For example,
> couldn't we just consider them removable as soon as the backend that owns
> them disappears?

Or perhaps go all the way and generalize that to rows that never
become visible outside their parent transaction.

As in, delete of rows created by the deleting transaction could clean
up, carefully to avoid voiding indexes and all that, but more
aggressively than regular deletes.