Re: [Postgres-xc-developers] Using killall in pgxc_ctl

[Michael P. <mic...@gm...>]

On Fri, Jul 18, 2014 at 3:26 PM, Pavan Deolasee
<pav...@gm...> wrote:
> I think its a bad idea to use killall to terminate existing processes. I
> noticed this for GTM, but the  same may apply to other kinds of processes
> too. In my case, I was setting up GTM master and standby on the same
> machine. pgxc_ctl was failing to start up GTM correctly. Upon investigation,
> I figured out that while initialising/starting GTM slave, it first kills any
> existing GTM processes using "killall gtm". This kills the GTM master as
> well.
>
> There are several issues with using killall
>
> 1. It may kill unrelated processes e.g. I'd a vim session on gtm_cmd.c and
> it got killed too
That's actually kind of funny, just laughed lonely in front of my screen.

> 2. It may kill processes belonging to another instance, if user is running
> multiple database clusters on the same machine
This one is less funny :(

> 3. killall -9 It doesn't do a clean shutdown which may cause issues
> I wonder why can't we just rely on -m immediate? If the process fails to
> respond to that, either we have a bug to fix or worst administrator can
> manually kill the processes he wants. Even if we have to use kill command,
> can we not read PID from the .pid file and send signal to that particular
> process only?
Clearly. Partially written WAL record is an example of a bad thing
that could happen for Postgres. For GTM there are for sure similar
race conditions with a standby. The same applies to Postgres as well.
The usual, recommended, way is to use pg_ctl stop -m immediate in the
worst case. Isn't XC bundled with gtm_ctl that could be used instead
of killall? That's the same as sending a SIGQUIT after scanning the
GTM PID though..

Regards,
-- 
Michael