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From: Michel Pelletier <pelletier.michel@gmail.com>
Date: Sun, 20 Oct 2024 20:29:13 -0700
Message-ID: <CACxu=vLXvpzN4X3k+9jsMt6ujuOvFVUSkA80t_cROSsF4y2jQQ@mail.gmail.com>
Subject: Re: Using Expanded Objects other than Arrays from plpgsql
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-general <pgsql-general@lists.postgresql.org>
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On Sun, Oct 20, 2024 at 10:13=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrote=
:

>
> I'm not sure.  It seems certain that if the object is already expanded
> (either R/W or R/O), the paths for that in plpgsql_exec_function could
> be taken regardless of its specific type.
>


> But it seems like we could get an easy win by adjusting
> plpgsql_exec_function along the lines of
>
> l. 549:
> -                    if (!var->isnull && var->datatype->typisarray)
> +                    if (!var->isnull)
>
> l. 564:
> -                        else
> +                        else if (var->datatype->typisarray)
>
> How far does that improve matters for you?
>

I tried this change and couldn't get it to work, on the next line:

if (!var->isnull)
{
    if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var->value)))

var->value might not be a pointer, as it seems at least from my gdb
scratching, but say an integer.  This segfaults on non-array but
non-expandable datum.

I guess this gets back into knowing if a flat thing is expandable or not.
I'm going to spend some more time looking at it, I haven't been in this
corner of Postgres before.

Another comment that caught my eye was this one:

https://github.com/postgres/postgres/blob/master/src/pl/plpgsql/src/pl_exec=
.c#L8304

Not sure what the implication is there.

-Michel

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Sun, Oct 20, 2024 at 10:13=E2=80=
=AFAM Tom Lane &lt;<a href=3D"mailto:tgl@sss.pgh.pa.us">tgl@sss.pgh.pa.us</=
a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0p=
x 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><b=
r>
I&#39;m not sure.=C2=A0 It seems certain that if the object is already expa=
nded<br>
(either R/W or R/O), the paths for that in plpgsql_exec_function could<br>
be taken regardless of its specific type.=C2=A0=C2=A0<br></blockquote><div>=
=C2=A0</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0=
.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
But it seems like we could get an easy win by adjusting<br>
plpgsql_exec_function along the lines of<br>
<br>
l. 549:<br>
-=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (=
!var-&gt;isnull &amp;&amp; var-&gt;datatype-&gt;typisarray)<br>
+=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 if (=
!var-&gt;isnull)<br>
<br>
l. 564:<br>
-=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 else<br>
+=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 else if (var-&gt;datatype-&gt;typisarray)<br>
<br>
How far does that improve matters for you?<br></blockquote><div><br></div><=
div>I tried this change and couldn&#39;t get it to work, on the next line:<=
/div><div><br></div><div>if (!var-&gt;isnull)<br>{<br>=C2=A0 =C2=A0 if (VAR=
ATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(var-&gt;value)))<br></div><div>=
<br></div><div>var-&gt;value might not be a pointer, as it seems at least f=
rom my gdb scratching, but say an integer.=C2=A0 This segfaults on non-arra=
y but non-expandable datum.</div><div><br></div><div>I guess this gets back=
 into knowing if a flat thing is expandable or not.=C2=A0 I&#39;m going to =
spend some more time looking at it, I haven&#39;t been in this corner of Po=
stgres before.</div><div><br></div><div>Another comment that caught my eye =
was this one:</div><div><br></div><div><a href=3D"https://github.com/postgr=
es/postgres/blob/master/src/pl/plpgsql/src/pl_exec.c#L8304">https://github.=
com/postgres/postgres/blob/master/src/pl/plpgsql/src/pl_exec.c#L8304</a><br=
></div><div>=C2=A0</div><div>Not sure what the implication is there.</div><=
div><br></div><div>-Michel</div></div></div>

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