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?
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
