Re: pg_ctl idempotent option

On Tue, Jan 15, 2013 at 9:36 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> On 1/14/13 10:22 AM, Tom Lane wrote:
>>> Also it appears to me that the hunk at lines 812ff is changing the
>>> default behavior, which is not what the patch is advertised to do.
>
>> True, I had forgotten to mention that.
>
>> Since it's already the behavior for start, another option would be to
>> just make it the default for stop as well and forget about the extra
>> options.

By default, (without idempotent option), if it finds the pid, it tries
to start one. If there is already one running, it exits with errorcode
1, otherwise it has already run the server.
814 exitcode = start_postmaster();
815 if (exitcode != 0)
816 {
817 write_stderr(_("%s: could not start server: exit code was %d\n"),
818 progname, exitcode);
819 exit(1);
820 }

What we can do under idempotent is to return with code 0 instead of
exit(1) above, thus not need the changes in the patch around line 812.
That will be more in-line with the description at
http://www.postgresql.org/message-id/1253165415.18853.32.camel@vanquo.pezone.net

> for example an exit
> code of 0 for an attempt to start a server which is already running
> or an attempt to stop a server which isn't running. (These are only
> two examples of differences between what is required of an LSB
> conforming init script and what pg_ctl does. Are we all in universal
> agreement to make such a change to pg_ctl?

anyway, +1 for making this as default option. Going that path, would
we be breaking backward compatibility? There might be scripts, (being
already used), which depend upon the current behaviour.

> I'm not sure whether there is a big use case for getting an
>> error code on stop if the server is already stopped.
>
> Actually, I seem to recall having had to hack Red Hat's initscript
> because the LSB standard requires that stopping a not-running server
> *not* be an error. So +1 for forgetting about the option entirely
> and just making it idempotent all the time.
>
> regards, tom lane
>
>
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--
Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Enterprise Postgres Company