From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)ru>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, David Steele <david(at)pgmasters(dot)net> |
Subject: | Re: [Patch] Temporary tables that do not bloat pg_catalog (a.k.a fast temp tables) |
Date: | 2016-08-15 00:57:55 |
Message-ID: | 20160815005755.gswdyjfob7dzw4yp@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-08-07 14:46:06 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > 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. It's obviously not a small change to get
there - and I don't think the patch upthread is really attacking the
relevant problems yet - but saying that we'll never have temp tables
without pg_class/pg_depend bloat seems to be pretty close to just giving
up. Having 8 byte oids (as explicit columns instead of magic? Or just
oid64?) and then reserving ranges for temp objects stored in a local
memory seems to be feasible. The pinning problem could potentially be
solved by "session lifetime" pins in pg_depend, which prevents dependent
objects being dropped. Obviously that's just spitballing; but I think
the problem is too big to just give up.
Andres
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