postgresql subtransactions error exception catch

gistfile1.txt

Frank Pachot
https://lnkd.in/dMPzDBWK

Laurenz Albe from cybertec-postgresql
https://lnkd.in/drp932PZ

Nikolay Samokhvalov from postgres ai
https://lnkd.in/dHmtVdT7


postgres=# do $BODY$
begin
 insert into demo (id) values(1);
 commit;
 insert into demo (id) values(1);
exception
  when unique_violation then
   raise notice 'ignoring duplicate';
end;
$BODY$;
ERROR:  cannot commit while a subtransaction is active
CONTEXT:  PL/pgSQL function inline_code_block line 4 at COMMIT


postgres=# do $BODY$
begin
 insert into demo (id) values(1);
 commit;
 insert into demo (id) values(1);
exception
  when others then
   raise notice 'ignoring duplicate';
end;
$BODY$;
NOTICE:  ignoring duplicate
DO

The reason you don't see the "subtransaction is active" error message is that your WHEN OTHERS block caught that exact error.

In PostgreSQL, a BEGIN ... EXCEPTION block creates an implicit subtransaction. When you try to COMMIT inside that block, PostgreSQL triggers a specific error: invalid_transaction_termination (SQLSTATE 2D000). Because your code uses WHEN OTHERS, it intercepts that error before it reaches your console, prints 'error', and exits gracefully.


postgres=# do $BODY$
begin
 insert into demo (id) values(1);
 commit;
 insert into demo (id) values(1);
exception
  when others then
   RAISE NOTICE 'Error Message: %', SQLERRM;
end;
$BODY$;
NOTICE:  Error Message: cannot commit while a subtransaction is active
DO