Re: Need Multixact Freezing Docs

Josh Berkus 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.

Great, thanks.

> josh=# select relname, age(relminmxid) from pg_class;
> relname | age
> -----------------------------------------+------------
> pg_statistic | 2147483647
> pg_type | 2147483647
> random | 2147483647
> dblink_pkey_results | 2147483647
> pg_toast_17395 | 2147483647
>
> ...
>
> So if age() doesn't mean anything, then how are users to know when the
> need to freeze?

I don't understand. Autovacuum will freeze this automatically when the
threshold is reached. Users don't need to do anything.

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