On Tue, Jan 31, 2017 at 9:53 AM, Higuchi, Daisuke
<higuchi.dais...@jp.fujitsu.com> wrote:
> Hello,
> This this is my first posting to the mailing list.
> I am interested in multiple hosts of libpq [1], then I found the bug in this 
> feature.
> When I set "target_session_attrs" to "any" and call PQsendQuery, my 
> application is succeeded.
> However, when I set "target_session_attrs" to "read-write" and call 
> PQsendQuery, "another command is already in progress" is occurred.
> I attached the test application to reproduce this problem.
> I think this is because PQgetResult is not called until PQgetResult has 
> returned a null pointer.
> So, I attached the patch for fix this.
> [1] 
> https://www.postgresql.org/message-id/flat/20150818041850.ga5...@wagner.pp.ru#20150818041850.ga5...@wagner.pp.ru
Interestingly, when I don't set PGPORT, PGHOST I get the same error
with the C program. The patch fixes the problem.

Per the documentation [1], "PQgetResult must be called repeatedly
until it returns a null pointer, indicating that the command is
done.". The code in PQgetResult() under CONNECTION_CHECK_WRITABLE
case, violates that. The patch fixes it. The patch however jumps to
keep_going without changing conn->status, which means that it will end
up again in the same case. While that's fine, may be we should use a
local loop on PQgetResult() to keep the code readable.

I would have added a test with the patch, but it seems we don't have
much tests in interfaces/libpq. The bug is pretty trivial and would
have been caught easily had we had any tests.

[1] https://www.postgresql.org/docs/devel/static/libpq-async.html

Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:

Reply via email to