Re: Need Multixact Freezing Docs

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?

> >> Also: how do I check the multixact age of a table? There doesn't seem
> >> to be any data for this ...
> >
> > pg_class.relminmxid is the oldest multixact value that might be present
> > in a table.
>
> On every database I've tested, age(relminmxid) returns int_max. So this
> is apparently broken.

Hmm, are you sure it's INT_MAX and not 4244967297? Heikki reported
that: http://www.postgresql.org/message-id/52401AEA.9000608@vmware.com
The absolute value is not important; I think that's mostly harmless. I
don't think applying age() to a multixact value is meaningful, though;
that's only good for Xids.

--
Álvaro Herrera http://www.2ndQuadrant.com/
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