Re: PG_RE_THROW is mandatory (was Re: jsonpath)

On 2019-02-06 13:09:59 -0300, Alvaro Herrera wrote:
> In https://postgr.es/m/1676.1548726280@sss.pgh.pa.us Tom Lane wrote:
>
> > Sure: every errcode we have is unsafe to treat this way.
> >
> > The backend coding rule from day one has been that a thrown error requires
> > (sub)transaction cleanup to be done to make sure that things are back in a
> > good state. You can *not* just decide that it's okay to ignore that,
> > especially not when invoking code outside the immediate area of what
> > you're doing.
>
> elog.h claims that PG_RE_THROW is "optional":
>
> /*----------
> * API for catching ereport(ERROR) exits. Use these macros like so:
> *
> * PG_TRY();
> * {
> * ... code that might throw ereport(ERROR) ...
> * }
> * PG_CATCH();
> * {
> * ... error recovery code ...
> * }
> * PG_END_TRY();
> *
> * (The braces are not actually necessary, but are recommended so that
> * pgindent will indent the construct nicely.) The error recovery code
> * can optionally do PG_RE_THROW() to propagate the same error outwards.
>
> This is obviously wrong; while we have a couple of codesites that omit
> it, it's not a generally available coding pattern. I think we should
> amend that comment. I propose: "The error recovery code must normally
> do PG_RE_THROW() to propagate the error outwards; failure to do so may
> leave the system in an inconsistent state for further processing."

Well, but it's ok not to rethrow if you do a [sub]transaction
rollback. I assume that's why it's framed as optional. We probably
should reference that fact?

Greetings,

Andres Freund