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

On Tue, Aug 23, 2016 at 7:11 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> On 08/22/2016 10:32 PM, Robert Haas wrote:
>>
>>
>> ...
>>
>> 1. The number of tables for which we would need to add a duplicate,
>> unlogged table is formidable. You need pg_attribute, pg_attrdef,
>> pg_constraint, pg_description, pg_type, pg_trigger, pg_rewrite, etc.
>> And the backend changes needed so that we used the unlogged copy for
>> temp tables and the permanent copy for regular tables is probably
>> really large.
>>
>> 2. You can't write to unlogged tables on standby servers, so this
>> doesn't help solve the problem of wanting to use temporary tables on
>> standbys.
>>
>> 3. While it makes creating temporary tables a lighter-weight
>> operation, because you no longer need to write WAL for the catalog
>> entries, there's probably still substantially more overhead than just
>> stuffing them in backend-local RAM. So the performance benefits are
>> probably fairly modest.
>>
>> Overall I feel like the development effort that it would take to make
>> this work would almost certainly be better-expended elsewhere. But of
>> course I'm not in charge of how people who work for other companies
>> spend their time...
>>
>
> 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.