Re: truncating pg_multixact/members

Robert Haas escribió:
> On Mon, Jan 20, 2014 at 1:39 PM, Alvaro Herrera
> <alvherre@2ndquadrant.com> wrote:
> > * I haven't introduced settings to tweak this per table for
> > autovacuum.  I don't think those are needed.  It's not hard to do,
> > however; if people opine against this, I will implement that.
>
> I can't think of any reason to believe that it will be less important
> to tune these values on a per-table basis than it is to be able to do
> the same with the autovacuum parameters.  Indeed, all the discussion
> on this thread suggests precisely that we have no real idea how to set
> these values yet, so more configurability is good.  Even if you reject
> that argument, I think it's a bad idea to start making xmax vacuuming
> and xmin vacuuming less than parallel; such decisions confuse users.

Yeah, I can relate to this argument.  I have added per-table
configurability to this, and also added the an equivalent of
autovacuum_freeze_max_age to force a for-wraparound full scan of a table
based on multixacts.

I haven't really tested this beyond ensuring that it compiles, and I
haven't changed the default values, but here it is in case someone wants
to have a look and comment --- particularly on the doc additions.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services