Re: [Bug fix] PQsendQuery occurs error when target_session_attrs is set to read-write

On Wed, Feb 15, 2017 at 1:31 AM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Wed, Feb 15, 2017 at 11:08 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> I think the patch as presented probably isn't quite what we want,
>> because it waits synchronously for the second result to be ready.
>> Note that the wait for the first result is asynchronous: we check
>> PQisBusy and return without progressing the state machine until the
>> latter returns false; only then do we call PQgetResult().
>
> OK, I have been poking at this problem. I think that we need to
> introduce a new state in ConnStatusType telling "please consume all
> results until PQgetResult returns NULL" which is CONNECTION_CONSUME in
> the patch attached. And as long as all the results are not consumed,
> the loop just keeps going. If more messages are being waited for with
> PGisBusy returning true, then the loop requests for more data to read
> by switching back to PGRES_POLLING_READING.
>
> By the way, I am noticing as well that libpq.sgml is missing a
> reference to CONNECTION_CHECK_WRITABLE. This should be present as
> applications calling PQconnectPoll() could face such a status. I have
> fixed this issue as well in the patch attached.

Great, thanks! This looks good to me, so committed. Is there any
chance you can use your amazing TAP-test-creation powers to do some
automated testing of this feature? For example, maybe we could at
least set up a master and a standby and somehow test that asking for a
read-only server picks the standby if it's first but asking for a
read-write server tries the standby and then switches to the master?
It would also be nice to test that probing a server that doesn't exist
fails, but I'm not sure how to create an IP/port combination that's
guaranteed to not work.

--
Robert Haas
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