Re: [RFC] building postgres with meson - v12

Hi,

On 2022-09-04 13:12:52 +0700, John Naylor wrote:
> On Fri, Sep 2, 2022 at 11:35 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> > Hi,
> >
> > On 2022-09-02 14:17:26 +0700, John Naylor wrote:
> > > On Thu, Sep 1, 2022 at 1:12 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > > [v12]
> > >
> > > +# Build a small utility static lib for the parser. This makes it easier to not
> > > +# depend on gram.h already having been generated for most of the other code
> > > +# (which depends on generated headers having been generated). The generation
> > > +# of the parser is slow...
> > >
> > > It's not obvious whether this is intended to be a Meson-only
> > > optimization or a workaround for something awkward to specify.
> >
> > It is an optimization. The parser generation is by far the slowest part of a
> > build. If other files can only be compiled once gram.h is generated, there's a
> > long initial period where little can happen. So instead of having all .c files
> > have a dependency on gram.h having been generated, the above makes only
> > scan.c, gram.c compilation depend on gram.h. It only matters for the first
> > compilation, because such dependencies are added as order-only dependencies,
> > supplanted by more precise compiler generated dependencies after.
>
> Okay, I think the comment could include some of this info for clarity.

Working on that.

> > It's still pretty annoying that so much of the build is initially idle,
> > waiting for genbki.pl to finish.
> >
> > Part of that is due to some ugly dependencies of src/common on backend headers
> > that IMO probably shouldn't exist (e.g. src/common/relpath.c includes
> > catalog/pg_tablespace_d.h).
>
> Technically, *_d.h headers are not backend, that's why it's safe to
> include them anywhere. relpath.c in its current form has to know the
> tablespace OIDs, which I guess is what you think is ugly. (I agree
> it's not great)

Yea, I'm not saying it's unsafe in a produces-wrong-results way, just that it
seems architecturally dubious / circular.

> > Looks like it'd not be hard to get at least the
> > _shlib version of src/common and libpq build without waiting for that. But for
> > all the backend code I don't really see a way, so it'd be nice to make genbki
> > faster at some point.
>
> The attached gets me a ~15% reduction in clock time by having
> Catalog.pm parse the .dat files in one sweep, when we don't care about
> formatting, i.e. most of the time:

Cool. Seems worthwhile.

Greetings,

Andres Freund