Re: Proof of concept: standalone backend with full FE/BE protocol

On 2013-12-05 23:01:28 +0200, Heikki Linnakangas wrote:
> On 12/05/2013 10:37 PM, Robert Haas wrote:
> >On Thu, Dec 5, 2013 at 3:05 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>It might be unpleasant to use in some cases, though.
> >
> >Why would there be more than a few cases in the first place? Who is
> >going to use this beyond psql, pg_dump(all), and pg_upgrade, and why?
>
> Well, you might want to use pgAdmin, or your other favorite admin tool. I'm
> not sure how well it would work, and I think it's OK if we say "sorry, can't
> do that", but it's not a crazy thing to want.

Pgadmin wouldn't work, it uses multiple connections for anything but the
most trivial tasks. You can't even send a manual sql query using only
one connection.
I think that's true for most of the non-trivial tools.

> >>Another issue is that we have too many variants of PQconnect
> >>already; which of them are we prepared to clone for this
> >>hypothetical new connection method?
> >
> >PQconnectdbParams, I assume. Isn't that the one to rule them all,
> >modulo async connect which I can't think is relevant here?

> Right. Not all of the parameters will make sense for a stand-alone backend
> though, like the hostname and port number. And I think you need need a new
> parameter to pass the path to the 'postgres' executable, unless we re-use
> the host parameter for that.

Hm. I'd guessed that we wouldn't use the connection string to pass down
the executable name and the datadir now that we're inventing a separate
function. But maybe that's unneccessary.

What parameters do we require to be set for that mode:
* path to postgres
* data directory
* database name (single mode after all)
* port, because of the shmem key? I'd say that's not important enough

I think we also need to be able to pass some additional parameters to
postgres:
- config_file, hba_file, ... might be required to start pg in some environments
- -P, -O , are sometimes required in cases single user mode is
neccessary for data recovery.

So I think we should just allow passing through arguments to postgres.

Not sure if we need anything but the pid of the postmaster be returned?

> >Or don't clone that one but instead have
> >PQnextConnectionShouldForkThisBinary('...') and let the psql/pg_dump
> >switch be --standalone=full-path-to-the-postgres-binary.

Yuck, that's ugly.

Greetings,

Andres Freund

--
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