Re: Getting rid of "unknown error" in dblink and postgres_fdw

On 12/21/2016 04:22 PM, Tom Lane wrote:
> Joe Conway <mail(at)joeconway(dot)com> writes:
>> I did notice that postgres_fdw has the following stanza that I don't see
>> in dblink:
>
>> 8<------------------
>> /*
>> * If we don't get a message from the PGresult, try the PGconn. This
>> * is needed because for connection-level failures, PQexec may just
>> * return NULL, not a PGresult at all.
>> */
>> if (message_primary == NULL)
>> message_primary = PQerrorMessage(conn);
>> 8<------------------
>
>> I wonder if the original issue on pgsql-bugs was a connection-level
>> failure rather than OOM? Seems like dblink ought to do the same.
>
> Oooh ... I had thought that code was in both, which was why I was having
> a hard time explaining the OP's failure. But I see you're right,
> which provides a very straightforward explanation for the report.
> I believe that if libpq is unable to malloc a PGresult, it will return
> NULL but put an "out of memory" message into the PGconn's error buffer.
> I had supposed that we'd capture and report the latter, but as the
> dblink code stands, it won't.
>
> In short, yes, please copy that bit into dblink.

The attached should do the trick I think. You think it is reasonable to
backpatch this part too?

Joe

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