Re: system views for walsender activity

On Mon, 2011-01-10 at 15:20 +0100, Magnus Hagander wrote:
> On Sun, Jan 9, 2011 at 15:53, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On Sun, 2011-01-09 at 12:52 +0100, Magnus Hagander wrote:
> >
> >> One thing I noticed is that it gives an interesting property to my
> >> patch for streaming base backups - they now show up in
> >> pg_stat_replication, with a streaming location of 0/0.
> >>
> >> If the view is named pg_stat_replication, we probably want to filter
> >> that out somehow. But then, do we want a separate view listing the
> >> walsenders that are busy sending base backups?
> >>
> >> For that matter, do we want an indication that separates a walsender
> >> not sending data from one sending that happens to be at location 0/0?
> >> Most will leave 0/0 really quickly, but a walsender can be idle (not
> >> received a command yet), or it can be running IDENTIFY_SYSTEM for
> >> example.
> >
> > I think we need a status enum. ('BACKUP', 'CATCHUP', 'STREAM') for the 3
> > phases of replication.
>
> That seems reasonable. But if we keep BACKUP in there, should we
> really have it called pg_stat_replication? (yeah, I know, I'm not
> giving up :P)
>
> (You'd need a 4th mode for WAITING or so, to indicate it's waiting for
> a command)

That's something different.

The 3 phases are more concrete.

BACKUP --> CATCHUP <---> STREAM

When you connect you either do BACKUP or CATCHUP. Once in CATCHUP mode
you never issue a BACKUP. Once we have caught up we move to STREAM. That
has nothing to do with idle/active.

--
Simon Riggs http://www.2ndQuadrant.com/books/
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