Re: Need Multixact Freezing Docs

On Thu, Aug 28, 2014 at 09:32:17AM -0700, Josh Berkus wrote:
> On 08/28/2014 09:09 AM, Alvaro Herrera wrote:
> > Josh Berkus wrote:
> >> On 04/16/2014 01:30 PM, Alvaro Herrera wrote:
> >>> Josh Berkus wrote:
> >>>>
> >>>>> You can see the current multixact value in pg_controldata output.  Keep
> >>>>> timestamped values of that somewhere (a table?) so that you can measure
> >>>>> consumption rate.  I don't think we provide SQL-level access to those
> >>>>> values.
> >>>>
> >>>> Bleh.  Do we provide SQL-level access in 9.4?  If not, I think that's a
> >>>> requirement before release.
> >>>
> >>> Yeah, good idea.  Want to propose a patch?
> >>
> >> Yeah, lemme dig into this.  I really think we need it for 9.4, feature
> >> frozen or not.
> 
> Got sidetracked by JSONB.

I had a look at this and came upon a problem --- there is no multi-xid
SQL data type, and in fact the system catalogs that store mxid values
use xid, e.g.:

	 relminmxid     | xid       | not null

With no mxid data type, there is no way to do function overloading to
cause age to call the mxid variant.

Should we use an explicit mxid_age() function name?  Add an mxid data
type?

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +