Re: Segmentation fault with core dump

On 2013-04-10 19:06:12 -0400, Tom Lane wrote:
> I wrote:
> > (Wanders away wondering just how much the regression tests exercise
> > holdable cursors.)
>
> And the answer is they're not testing this code path at all, because if
> you do
>     DECLARE c CURSOR WITH HOLD FOR ...
>     FETCH ALL FROM c;
> then the second query executes with a portal (and resource owner)
> created to execute the FETCH command, not directly on the held portal.
>
> After a little bit of thought I'm not sure it's even possible to
> reproduce this problem with libpq, because it doesn't expose any way to
> issue a bare protocol Execute command against a pre-existing portal.
> (I had thought psqlOBC went through libpq, but maybe it's playing some
> games here.)
>
> Anyway, I'm thinking the appropriate fix might be like this
>
> -        CurrentResourceOwner = portal->resowner;
> +        if (portal->resowner)
> +            CurrentResourceOwner = portal->resowner;
>
> in several places in pquery.c; that is, keep using
> TopTransactionResourceOwner if the portal doesn't have its own.
>
> A more general but probably much more invasive solution would be to fake
> up an intermediate portal when pulling data from a held portal, to
> more closely approximate the explicit-FETCH case.

We could also allocate a new resowner for the duration of that
transaction. That would get reassigned to the transactions resowner in
PreCommit_Portals (after a slight change there).
That actually seems simple enough?

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
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