Re: Bad UI design: pg_ctl and data_directory

On Wed, Jun 1, 2011 at 7:07 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> Excerpts from Robert Haas's message of mié jun 01 18:22:56 -0400 2011:
>>> ISTM that it would be useful to run postgres in a mode where it
>>> doesn't actually try to start up the database, but parses
>>> postgresql.conf and then exits, perhaps printing out the value of a
>>> certain GUC as it does so.  In this case, data_directory.
>
>> I had the same thought, and wondered if we could use the feature
>> elsewhere.
>
> This was suggested quite some time ago, IIRC, but we never got round to it.
>
> The main problem in the current context is that it only fixes the issue
> so long as you ignore the possibility that relevant values were
> specified on the command line or via environment variables, rather than
> coming directly from the config file.  PGDATA is thus a particular
> hazard here: all you need is to be running with a different PGDATA
> setting in your environment than was used when "pg_ctl start" was
> issued, and you're hosed.

I guess I'm missing something here. If you change PGDATA, you're
going to be working on a different cluster, but that's what you asked
for. I guess there could be a problem if you used pg_ctl -D dir
start, and postgres --tell-me-the-data-dir relied on PGDATA in telling
you what the data directory should be, but that seems simple to work
around: just have -D dir set $PGDATA before invoking postgres.

--
Robert Haas
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