Re: Making background psql nicer to use in tap tests

On 2023-01-30 Mo 19:00, Andres Freund wrote:
> Hi,
>
> On 2023-01-30 15:06:46 -0500, Tom Lane wrote:
>> Andres Freund<andres(at)anarazel(dot)de> writes:
>>> It's annoyingly hard to wait for the result of a query in a generic way with
>>> background_psql(), and more generally for psql. background_psql() uses -XAtq,
>>> which means that we'll not get "status" output (like "BEGIN" or "(1 row)"),
>>> and that queries not returning anything are completely invisible.
>> Yeah, the empty-query-result problem was giving me fits recently.
>> +1 for wrapping this into something more convenient to use.
> I've hacked some on this. I first tried to just introduce a few helper
> functions in Cluster.pm, but that ended up being awkward. So I bit the bullet
> and introduced a new class (in BackgroundPsql.pm), and made background_psql()
> and interactive_psql() return an instance of it.
>
> This is just a rough prototype. Several function names don't seem great, it
> need POD documentation, etc.

Since this class is only intended to have instances created from
Cluster, I would be inclined just to put it at the end of Cluster.pm
instead of creating a new file. That makes it clearer that the new
package is not standalone. We already have instances of that.

The first param of the constructor is a bit opaque. If it were going to
be called from elsewhere I'd want something a bit more obvious, but I
guess we can live with it here. An alternative might be
multiple_constructors (e.g. new_background, new_interactive) which use a
common private routine.

Don't have comments yet on the other things, will continue looking.

cheers

andrew

--
Andrew Dunstan
EDB:https://www.enterprisedb.com