Обсуждение: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

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Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

От
"Delaney, Ed"
Дата:

I do not have pg 13.6 installed yet as we just upgraded all of our systems from 11 to 13.5 but I suspect it will be the same.

 

Here is the test script:

select version();

create or replace procedure foo ( inout p_inout_parameter character varying default null::character varying)

language plpgsql

as $procedure$

declare

lv_this_goes_out character varying;

begin

   lv_this_goes_out := 'I am the walrus';

   raise notice 'foo called';

   p_inout_parameter := lv_this_goes_out;

end;

$procedure$;

 

 

create or replace procedure bar ()

language plpgsql

as $procedure$

declare

  lv_somestring character varying (4000);

begin

   call foo(lv_somestring::character varying);  -- note cast

   raise notice 'lv_somestring: %', lv_somestring;

end;

$procedure$;

 

-- this works in pg11 and fails in pg13

do $$

declare l_var text;

begin

   call bar ();

end;

$$;

drop routine if exists foo;

drop routine if exists bar;

 

Expected output: (pg 11.13)

                                                             version                                                               

------------------------------------------------------------------------------------------------------------------------------------

 PostgreSQL 11.13 (Ubuntu 11.13-1.pgdg20.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit

(1 row)

 

CREATE PROCEDURE

CREATE PROCEDURE

psql:/Users/edelaney/Desktop/boxsync/wip/typecast-arguments-bug.sql:32: NOTICE:  foo called

psql:/Users/edelaney/Desktop/boxsync/wip/typecast-arguments-bug.sql:32: NOTICE:  lv_somestring I am the walrus

DO

DROP ROUTINE

DROP ROUTINE

 

Actual output: pg 13.15

                                                             version                                                              

----------------------------------------------------------------------------------------------------------------------------------

 PostgreSQL 13.5 (Ubuntu 13.5-2.pgdg20.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0, 64-bit

(1 row)

 

CREATE PROCEDURE

CREATE PROCEDURE

psql:/Users/edelaney/Desktop/boxsync/wip/typecast-arguments-bug.sql:32: ERROR:  procedure parameter "p_inout_parameter" is an output parameter but corresponding argument is not writable

CONTEXT:  PL/pgSQL function bar() line 5 at CALL

SQL statement "CALL bar ()"

PL/pgSQL function inline_code_block line 4 at CALL

psql:/Users/edelaney/Desktop/boxsync/wip/typecast-arguments-bug.sql:33: ERROR:  current transaction is aborted, commands ignored until end of transaction block

psql:/Users/edelaney/Desktop/boxsync/wip/typecast-arguments-bug.sql:34: ERROR:  current transaction is aborted, commands ignored until end of transaction block

 

While no explicit cast is actually required, we have a very large amount of generated code that uses explicit type casting this way.

 

Ed Delaney (he/him) | Principal Architect

 

Re: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

От
"David G. Johnston"
Дата:
On Mon, Feb 14, 2022 at 3:50 PM Delaney, Ed <Ed.Delaney@ellucian.com> wrote:

I do not have pg 13.6 installed yet as we just upgraded all of our systems from 11 to 13.5 but I suspect it will be the same.

 

declare

  lv_somestring character varying (4000);

begin

   call foo(lv_somestring::character varying);  -- note cast


While no explicit cast is actually required, we have a very large amount of generated code that uses explicit type casting this way.



I'm unsure about the regression but in fact the explicit cast is simply incorrect conceptually.  You are supposed to be supplying a variable to the call.  What you are supplying is a constant.  That constant has the same value as the variable but is not itself a variable and even has a different type.  If you write: SELECT lv_somestring::varchar(1) you will get back the first character of the max 4,000 character value presently in the variable lv_somestring.  But you will not be changing the value stored in lv_somestring.  Extend that concept to CALL and you can see why the error you are being shown in v13 is correct.

David J.

Re: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

От
Tom Lane
Дата:
"Delaney, Ed" <Ed.Delaney@ellucian.com> writes:
> create or replace procedure bar ()
> language plpgsql
> as $procedure$
> declare
>   lv_somestring character varying (4000);
> begin
>    call foo(lv_somestring::character varying);  -- note cast
>    raise notice 'lv_somestring: %', lv_somestring;
> end;
> $procedure$;

I think you're out of luck on that.  Releases before last November
ignored that cast entirely, thinking it a no-op.  Current releases
do not ignore it, recognizing that in fact it has to be understood
as casting to varchar-of-unspecified-length.  But then the argument
isn't a bare variable anymore.

We debated about whether to back-patch such a behavioral change,
and maybe we shouldn't have.  But there are scenarios in which
the old behavior makes it just impossible to do things, eg you
may not be able to get a UNION to produce the desired type.
On balance we felt this was a bug fix.

            regards, tom lane

Re: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

От
"Delaney, Ed"
Дата:

Thanks for the timely replies.

I've found that either removing the length specification or the cast addresses the issue.
So this all makes sense to me.


I could not find a reference to this change in the release notes, but since it is a breaking change, perhaps it should be noted?

regards

Ed

 

From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Monday, February 14, 2022 at 6:28 PM
To: Delaney, Ed <Ed.Delaney@ellucian.com>
Cc: pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: [EXT]: Re: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

"Delaney, Ed" <Ed.Delaney@ellucian.com> writes:
> create or replace procedure bar ()
> language plpgsql
> as $procedure$
> declare
>   lv_somestring character varying (4000);
> begin
>    call foo(lv_somestring::character varying);  -- note cast
>    raise notice 'lv_somestring: %', lv_somestring;
> end;
> $procedure$;

I think you're out of luck on that.  Releases before last November
ignored that cast entirely, thinking it a no-op.  Current releases
do not ignore it, recognizing that in fact it has to be understood
as casting to varchar-of-unspecified-length.  But then the argument
isn't a bare variable anymore.

We debated about whether to back-patch such a behavioral change,
and maybe we shouldn't have.  But there are scenarios in which
the old behavior makes it just impossible to do things, eg you
may not be able to get a UNION to produce the desired type.
On balance we felt this was a bug fix.

                        regards, tom lane

Re: Postgres 13.5 out parameter argument with explicit cast fails with argument is not writable

От
Tom Lane
Дата:
"Delaney, Ed" <Ed.Delaney@ellucian.com> writes:
> I could not find a reference to this change in the release notes, but since it is a breaking change, perhaps it
shouldbe noted? 

The 2021-11-11 release notes all say

  * Don't discard a cast to the same type with unspecified type modifier (Tom Lane)

    For example, if column f1 is of type numeric(18,3), the parser used to
    simply discard a cast like f1::numeric, on the grounds that it would
    have no run-time effect. That's true, but the exposed type of the
    expression should still be considered to be plain numeric, not
    numeric(18,3). This is important for correctly resolving the type of
    larger constructs, such as recursive UNIONs.

            regards, tom lane