On 29/07/14 18:51, Robert Haas wrote:
On Mon, Jul 28, 2014 at 1:50 PM, Andres Freund <and...@2ndquadrant.com> wrote:
What I'm thinking of is providing an actual API for the writes instead
of hooking into the socket API in a couple places. I.e. have something
like
typedef struct DestIO DestIO;
struct DestIO
{
void (*flush)(struct DestIO *io);
int (*putbytes)(struct DestIO *io, const char *s, size_t len);
int (*getbytes)(struct DestIO *io, const char *s, size_t len);
...
}
and do everything through it. I haven't thought much about the specific
API we want, but abstracting the communication properly instead of
adding hooks here and there is imo much more likely to succeed in the
long term.
This sounds suspiciously like the DestReceiver thing we've already
got, except that the DestReceiver only applies to tuple results, not
errors and notices and so on. I'm not totally unamenable to a bigger
refactoring here, but right now it looks to me like a solution in
search of a problem. The hooks are simple and seem to work fine; I
don't want to add notation for its own sake.
I am not sure if what Andres proposed is the right solution, but I do
agree here that the hook definitely isn't.
I am also not sure that I like the pq_redirect_to_shm_mq being directly
exposed for use in bgworker, what I would like is to have elog interface
to which you tell that you want errors sent to shm_mq handle and that
one would then do the necessary calls (It's basically same principle but
for the sake of cleanliness/correctness I think it should be elog and
not pq from the point of bgworker).
So the interface needs work.
I do agree that we don't need two way communication over this channel, I
think the dsm_mq can be used directly quite well for generic usecase.
Otherwise I like the patch, and I am glad you also made the GUC
save/restore infrastructure.
Please don't forget to add this to next commitfest.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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