Re: [Patch] Temporary tables that do not bloat pg_catalog (a.k.a fast temp tables) - Mailing list pgsql-hackers

Why are you sending this off-list?  Please let's keep the discussion
on the mailing list.  I suggest resending this there.

On Mon, Aug 15, 2016 at 5:01 AM, Aleksander Alekseev
<a.alekseev@postgrespro.ru> wrote:
>> > >>> I think the whole idea of a fast temporary table is that there
>> > >>> are no catalog entries.  If there are no catalog entries, then
>> > >>> dependencies are not visible.  If there ARE catalog entries, to
>> > >>> what do they refer? Without a pg_class entry for the table,
>> > >>> there's no table OID upon which to depend.
>> >
>> > >> TBH, I think that the chances of such a design getting committed
>> > >> are not distinguishable from zero.  Tables have to have OIDs;
>> > >> there is just too much code that assumes that.  And I seriously
>> > >> doubt that it will work (for any large value of "work") without
>> > >> catalog entries.
>> >
>> > > That seems a bit too defeatist.
>> >
>> > Huh?  I didn't say we shouldn't work on the problem --- I just
>> > think that this particular approach isn't good.  Which you seemed
>> > to agree with.
>>
>> I took your statement to mean that they need a pg_class entry - even
>> if there were a partial solution to the pg_depend problem allowing to
>> avoid pg_attribute entries, tha't still not really be a solution. If
>> that's not what you mean, sorry - and nice that we agree ;)
>>
>>
>
> Just to keep things sane I would like to remind that in this concrete
> patch there _are_ catalog entries:
>
> ```
> [...]
> This file contents imlementation of special type of temporary tables ---
> fast temporary tables (FTT). From user perspective they work exactly as
> regular temporary tables. However there are no records about FTTs in
> pg_catalog. These records are stored in backend's memory instead and
> mixed with regular records during scans of catalog tables. We refer to
> corresponding tuples of catalog tables as "in-memory" or "virtual"
> tuples and to all these tuples together --- as "in-memory" or "virtual"
> catalog.
> [...]
> ```
>
> As Tom pointed out a lot of PL/pgSQL code would stop working otherwise.
> Also I mentioned that in this case even \d and \d+ would not work.
>
> I personally find this discussion very confusing. Maybe we should
> concentrate on a concrete patch instead of some abstract ideas and
> topics that are still open.
>
> For instance it surprises me that apparently there is no one who
> objects "lets make all temporary tables fast temporary tables" idea.
> Since in this case code would use more memory for keeping a virtual
> catalog wouldn't it be considered a major change of behavior that could
> break someones production environment?
>
> --
> Best regards,
> Aleksander Alekseev



-- 
Robert Haas
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