Re: [PATCH] pg_isready (was: [WIP] pg_ping utility)

On Jan 26, 2013 6:56 PM, "Craig Ringer" <craig(at)2ndquadrant(dot)com> wrote:
>
> On 01/27/2013 06:20 AM, Phil Sorber wrote:
> > On Sat, Jan 26, 2013 at 4:37 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:
> >> 2013/1/26 Phil Sorber <phil(at)omniti(dot)com>:
> >>> On Sat, Jan 26, 2013 at 12:39 PM, Pavel Stehule <
pavel(dot)stehule(at)gmail(dot)com> wrote:
> >>>> 2013/1/26 Phil Sorber <phil(at)omniti(dot)com>:
> >>>>> On Sat, Jan 26, 2013 at 11:53 AM, Pavel Stehule <
pavel(dot)stehule(at)gmail(dot)com> wrote:
> >>>>>> 2013/1/26 Phil Sorber <phil(at)omniti(dot)com>:
> >>>>>>> On Sat, Jan 26, 2013 at 4:02 AM, Pavel Stehule <
pavel(dot)stehule(at)gmail(dot)com> wrote:
> >>>>>>>> Hello
> >>>>>>>>
> >>>>>>>> We now haw to solve small puppet issue, because our puppets try
to
> >>>>>>>> start server too early, when old instance live still.
> >>>>>>>>
> >>>>>>>> Maybe some new parameter - is_done can be useful.
> >>>>>>>>
> >>>>>>> What about something like:
> >>>>>>> pg_isready; while [ $? -ne 2 ]; do sleep 1; pg_isready; done
> >>>>>> it is not enough - server is done in a moment, where can be started
> >>>>>> again - or when we can do safe copy of database data directory.
> >>>>>>
> >>>>> I guess i am not completely understanding the case you are trying to
> >>>>> solve. Can you explain a bit further?
> >>>> We use puppets and due some simplification we cannot to use reload
> >>>> when configuration is changed. Our puppets has not enough
intelligence
> >>>> to understand when is reload enough and when is restart necessary. So
> >>>> any change to configuration require restarting postgres. I don't know
> >>>> why "service restart" are not used. I believe so our puppet guru know
> >>>> it. It just do sequence STOP:START Now puppets are "smart" and able
> >>>> to wait for time, when server is ready. But there are missing simple
> >>>> test if server is really done and I see a error messages related to
> >>>> too early try to start. So some important feature can be verification
> >>>> so server is really done.
> >>>>
> >>>> We can do it with test on pid file now - and probably we will use it.
> >>>> But I see so this is similar use case (in opposite direction)
> >>>>
> >>> I guess I am still not clear why you can't do:
> >>>
> >>> stop_pg_via_puppet
> >>> pg_isready
> >>> while [ $? -ne 2 ]
> >>> do
> >>> sleep 1
> >>> pg_isready
> >>> done
> >>> do_post_stop_things
> >>> start_pg_via_puppet
> >>>
> >> because ! pg_isready <> pg_isdone
> >>
> > So you are proposing a different utility? Sorry, I thought you were
> > proposing a new option to pg_isready. What would pg_isdone be testing
> > for specifically? Is this something that would block until it has
> > confirmed a shutdown?
>
> That's what it sounds like - confirming that PostgreSQL is really fully
> shut down.
>
> I'm not sure how you could do that over a protocol connection, myself.
> I'd just read the postmaster pid from the pidfile on disk and then `kill
> -0` it in a delay loop until the `kill` command returns failure. This
> could be a useful convenience utility but I'm not convinced it should be
> added to pg_isready because it requires local and possibly privileged
> execution, unlike pg_isready's network based operation. Privileges could
> be avoided by using an aliveness test other than `kill -0`, but you
> absolutely have to be local to verify that the postmaster has fully
> terminated - and it wouldn't make sense for a non-local process to care
> about this anyway.
>

Maybe something to add to pg_ctl?

> --
> Craig Ringer http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>