From: "Drouvot, Bertrand" <bdrouvot@amazon.com>
Subject: [BUG]: segfault during update
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
Message-ID: <db5d97c8-f48a-51e2-7b08-b73d5434d425@amazon.com>
Date: Sun, 8 Nov 2020 17:30:15 +0100
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Hi hackers,

Here is a scenario that produces segfault during update (on version 12 
and 13):

create table bdttrig (created_at timestamp without time zone not null 
default now(),col1 bool not null default false, col2 text not null 
default 'def', col3 char(6) not null default 'bdtbdt');
CREATE TABLE

CREATE or replace FUNCTION trigger_function()
RETURNS TRIGGER
LANGUAGE PLPGSQL
AS $$
BEGIN
IF (NEW != OLD) THEN
NEW.created_at = OLD.created_at;
RETURN NEW;
END IF;
RETURN OLD;
END;
$$
;

CREATE FUNCTION

create trigger bdt_trigger before update on bdttrig for each row EXECUTE 
function trigger_function();

CREATE TRIGGER

insert into bdttrig(col1) values (true);

INSERT 0 1

alter table bdttrig add column col4 text  not null default 'default';

ALTER TABLE

alter table bdttrig drop column col2;

ALTER TABLE

update bdttrig  set col1 = true;
server closed the connection unexpectedly
         This probably means the server terminated abnormally
         before or while processing the request.

I did some digging and found out and tested that the issue is fixed by 
this commit: 
https://github.com/postgres/postgres/commit/20d3fe9009ddbbbb3da3a2da298f922054b43f8c

So, we would need to back port this commit on 12 and 13.

Thanks

Bertrand


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    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
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  <body>
    <p>Hi hackers,</p>
    <p>Here is a scenario that produces segfault during update (on
      version 12 and 13):<br>
    </p>
    <p>create table bdttrig (created_at timestamp without time zone not
      null default now(),col1 bool not null default false, col2 text not
      null default 'def', col3 char(6) not null default 'bdtbdt');<br>
      <font face="Courier New">CREATE TABLE</font></p>
    <p>CREATE or replace FUNCTION trigger_function()<br>
      RETURNS TRIGGER<br>
      LANGUAGE PLPGSQL<br>
      AS $$<br>
      BEGIN<br>
      IF (NEW != OLD) THEN<br>
      NEW.created_at = OLD.created_at;<br>
      RETURN NEW;<br>
      END IF;<br>
      RETURN OLD;<br>
      END;<br>
      $$<br>
      ;</p>
    <p><font face="Courier New">CREATE FUNCTION</font></p>
    <p>create trigger bdt_trigger before update on bdttrig for each row
      EXECUTE function trigger_function();</p>
    <p><font face="Courier New">CREATE TRIGGER</font></p>
    <p>insert into bdttrig(col1) values (true);</p>
    <p><font face="Courier New">INSERT 0 1</font></p>
    <p>alter table bdttrig add column col4 text  not null default
      'default';</p>
    <p><font face="Courier New">ALTER TABLE</font></p>
    <p>alter table bdttrig drop column col2;</p>
    <p><font face="Courier New">ALTER TABLE</font></p>
    <p>update bdttrig  set col1 = true;<br>
      <font face="Courier New">server closed the connection unexpectedly<br>
                This probably means the server terminated abnormally<br>
                before or while processing the request.</font></p>
    <p>I did some digging and found out and tested that the issue is
      fixed by this commit:
<a class="moz-txt-link-freetext" href="https://github.com/postgres/postgres/commit/20d3fe9009ddbbbb3da3a2da298f922054b43f8c">https://github.com/postgres/postgres/commit/20d3fe9009ddbbbb3da3a2da298f922054b43f8c</a></p>
    <p>So, we would need to back port this commit on 12 and 13.</p>
    <p>Thanks</p>
    <p>Bertrand<br>
    </p>
  </body>
</html>

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