Re: Need Multixact Freezing Docs

On Tue, Sep 2, 2014 at 8:18 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> 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?

Maybe both. But mxid_age() is probably the simpler way forward just to start.

--
Robert Haas
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