Date: Wed, 16 Apr 2014 17:45:38 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Josh Berkus <josh@agliodbs.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Need Multixact Freezing Docs
Message-ID: <20140416204538.GR5822@eldon.alvh.no-ip.org>
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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


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