On 2016/04/13 3:14, Robert Haas wrote:
I'm wondering why we are fixing this specific case and not any of the
other calls to PQexec() or PQexecParams() in postgres_fdw.c.

I mean, many of those instances are cases where the query isn't likely
to run for very long, but certainly "FETCH %d FROM c%u" is in theory
just as bad as the new code introduced in 9.6.  In practice, it
probably isn't, because we're probably only fetching 50 rows at a time
rather than potentially a lot more, but if we're fixing this code up
to be interrupt-safe, maybe we should fix it all at the same time.
Even for the short-running queries like CLOSE and DEALLOCATE, it seems
possible that there could be a network-related hang which you might
want to interrupt.

Actually, I was wondering, too, but I didn't propose that because, as far as I know, there are no reports from the field. But I agree with you.

How about we encapsulate the while (PQisBusy(...)) loop into a new
function pgfdw_get_result(), which can be called after first calling
PQsendQueryParams()?  So then this code will say dmstate->result =
pgfdw_get_result(dmstate->conn).  And we can do something similar for
the other call to PQexecParams() in create_cursor().  Then let's also
add something like pgfdw_exec_query() which calls PQsendQuery() and
then pgfdw_get_result, and use that to replace all of the existing
calls to PQexec().

Then all the SQL postgres_fdw executes would be interruptible, not
just the new stuff.

Seems like a good idea.  Will do.

Best regards,
Etsuro Fujita

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