Async queries pretending to be synchronous

In investigating #3656 I found the initial problem to be that when running
in a container, Gunicorn will kill the worker process if a thread doesn't
respond for 30 seconds by default. I fixed that by making the timeout match
the application session timeout, but it revealed another issue.

Given the function below (from the ticket), if you open the query tool and
run:

SELECT 1; SELECT fails_after(30);

the async query actually blocks for 30 seconds in the cur.execute() call in
execute_async() in connection.py (line 968). This causes the entire app to
hang (watch the dashboard requests pile up in pending state in the network
tab of the browser dev tools).

If you run just the second SELECT, it works as expected, as does running
something like:

SELECT 1; SELECT pg_sleep(30);

Anyone have any idea what's going on?

CREATE OR REPLACE FUNCTION fails_after(s integer)
RETURNS text AS $$
begin
raise notice 'Entered';
perform pg_sleep(s);
raise '!!!';
end;
$$ LANGUAGE plpgsql;

--
Dave Page
Blog: http://pgsnake.blogspot.com
Twitter: @pgsnake

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