Re: Making background psql nicer to use in tap tests

Hi,

On 2023-01-30 15:06:46 -0500, Tom Lane wrote:

Andres Freund <andres@anarazel.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