Re: Add sub-transaction overflow status in pg_stat_activity

On Fri, Dec 17, 2021 at 09:00:04AM +0530, Dilip Kumar wrote:
> On Tue, Dec 14, 2021 at 3:57 AM Bossart, Nathan <bossartn@amazon.com> wrote:
> >
> > On 12/13/21, 6:30 AM, "Dilip Kumar" <dilipbalaut@gmail.com> wrote:
> > > On Tue, Dec 7, 2021 at 11:11 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > >> Since I think this field is usually not interesting to most users of
> > >> pg_stat_activity, maybe this should instead be implemented as a function like
> > >> pg_backend_get_subxact_status(pid).
> > >>
> > >> People who want to could use it like:
> > >> SELECT * FROM pg_stat_activity psa, pg_backend_get_subxact_status(pid) sub;
> > >
> > > I have provided two function, one for subtransaction counts and other
> > > whether subtransaction cache is overflowed or not, we can use like
> > > this,  if we think this is better way to do it then we can also add
> > > another function for the lastOverflowedXid
> >
> > The general approach looks good to me.  I think we could have just one
> > function for all three values, though.
>
> If we create just one function then the output type will be a tuple
> then we might have to add another view on top of that.  Is there any
> better way to do that?

I don't think you'd need to add a view on top of it.

Compare:

postgres=# SELECT 1, pg_config() LIMIT 1;
 ?column? |         pg_config         
----------+----------------------------
        1 | (BINDIR,/usr/pgsql-14/bin)

postgres=# SELECT 1, c FROM pg_config() c LIMIT 1;
 ?column? |             c             
----------+----------------------------
        1 | (BINDIR,/usr/pgsql-14/bin)

postgres=# SELECT 1, c.* FROM pg_config() c LIMIT 1;
 ?column? |  name  |      setting     
----------+--------+-------------------
        1 | BINDIR | /usr/pgsql-14/bin