MIME-Version: 1.0
References: <CACxu=vJaKFNsYxooSnW1wEgsAO5u_v1XYBacfVJ14wgJV_PYeg@mail.gmail.com>
 <1342498.1729444411@sss.pgh.pa.us> <CACxu=vLXvpzN4X3k+9jsMt6ujuOvFVUSkA80t_cROSsF4y2jQQ@mail.gmail.com>
 <1445998.1729482404@sss.pgh.pa.us> <CACxu=vKEF8Qa-OaADFxf0uMg-xw6gH_CNCWd2s+xaqh-gY4=xg@mail.gmail.com>
 <2062830.1729625620@sss.pgh.pa.us> <2265411.1729699470@sss.pgh.pa.us>
 <CACxu=v++HNmss59yGUDkRny7g=M8tZ2YXF07AUXqKVGqcSfxGQ@mail.gmail.com>
 <2354718.1729737539@sss.pgh.pa.us> <2581216.1729794746@sss.pgh.pa.us>
 <CACxu=v+dn37zr8gx5xNP-EZY3OLtGLTHrbx_ZkCQc40HpyMLKA@mail.gmail.com>
 <1948345.1730500073@sss.pgh.pa.us> <CACxu=vL7i_U_iSNpREe8eCAMEyKHuPpk9THRpBhk+ar0U1EdOw@mail.gmail.com>
 <CACxu=vKLc6f5N8_DR58LKkE1eohWSxTvThTeGsLm7p7QH1aFBA@mail.gmail.com>
 <CACxu=vJf2S=ysun_h=zmYNu6oUM47+egbpX5mMC0X9BJK=EQwQ@mail.gmail.com>
 <CACxu=vK+S6BXN8ZYyBvqQBWrcwHXqtue1-ZuKO3+XtHGBYcDUQ@mail.gmail.com>
 <CAFj8pRCd6xcH-AYEyHFdGdU89O9JjZ-v-pyQnOwd9zNJkCEdhQ@mail.gmail.com>
 <3797606.1732045516@sss.pgh.pa.us> <CACxu=vJ1UeXPjPOzfT2E=tFpSCxPxcB7hgfqHYmefJWh3ZXPew@mail.gmail.com>
 <1417389.1736964543@sss.pgh.pa.us> <CACxu=vKModwqSpEjpn-ur1uMAEYkcd-i8CvNsH-z9=dk7F7YQw@mail.gmail.com>
 <3363452.1737483125@sss.pgh.pa.us> <0AC229FA-A3F1-43FD-B0DC-A46A73FEAFF7@yandex-team.ru>
 <931398.1737905825@sss.pgh.pa.us> <38A31221-C1C4-4846-9709-D66ACD76E87A@yandex-team.ru>
 <46876.1737918281@sss.pgh.pa.us>
In-Reply-To: <46876.1737918281@sss.pgh.pa.us>
From: Pavel Borisov <pashkin.elfe@gmail.com>
Date: Fri, 31 Jan 2025 00:32:03 +0400
Message-ID: <CALT9ZEGy5+GNQUtR80BPL7k-Qi47sqwPLnN_dOaQUW5UbxcTGA@mail.gmail.com>
Subject: Re: Using Expanded Objects other than Arrays from plpgsql
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>, Michel Pelletier <pelletier.michel@gmail.com>, 
	Pavel Stehule <pavel.stehule@gmail.com>, pgsql-hackers@lists.postgresql.org
Content-Type: text/plain; charset="UTF-8"
Archived-At: <https://www.postgresql.org/message-id/CALT9ZEGy5%2BGNQUtR80BPL7k-Qi47sqwPLnN_dOaQUW5UbxcTGA%40mail.gmail.com>
Precedence: bulk

Hi, Michel and Tom!

On Sun, 26 Jan 2025 at 23:04, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Andrey Borodin <x4mmm@yandex-team.ru> writes:
> > On 26 Jan 2025, at 20:37, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> Maybe we should recast it as an action.  What do you think of
> >> "mark_expr_as_assignment_source"?
>
> > Sounds better to me. I found no examples of similar functions nether in pl_gram.y, nor in gram.y, so IMO mark_expr_as_assignment_source() is the best candidate.
>
> WFM, I'll make it so in next version.
>
> > Got it, many thanks for the explanation.
>
> I'll see about incorporating more of that in the comments, too.
>
> > I wonder if you plan similar optimizations for array_cat(), array_remove() etc?
> > +   a := a || a; -- not optimizable
> > Why is it not optimizable? Because there is no support function, because array_cat() has no support function, or something else?
>
> plpgsql won't attempt to optimize it because "a" is referenced twice
> and there is no support function that might say it's safe anyway.
>
> array_cat doesn't currently have any special smarts about expanded
> arrays, so it's all moot because the arrays would get flattened
> on the way into it.  If we did improve it to be able to cope with
> expanded arrays, I'm not real sure that it could safely manage an
> in-place update where the two inputs are the same array --- at
> the least, some extreme care would be needed to get the right
> answers.
>
> I'm not real excited about optimizing additional array operations
> anyway.  Maybe some more will get done at some point, but I don't
> see that as part of this work.
>
>                         regards, tom lane

I started looking at the patchset.
Recently it got conflicts with changes to yyparse (473a575e05979b4db).
Could you rebase it and also do naming changes proposed by Andrew
Borodin, which I definitely agree with?

Regards,
Pavel Borisov