As per documentation http://initd.org/psycopg/docs/advanced.html Copy commands are not supported in asynchronous mode, but this will be probably implemented in a future release. In pgAdmin4 (open source) we have used async connection to run the SQL query on PostgreSQL database and uses poll() function to poll the results. When user runs any COPY command application hangs at poll() function.
If copy command not supported then at least it should not hang the application. poll() function should return the proper error message.
Can you please provide that fix until support for copy command won't come.
Uhm, I see:
In [2]: cnn = psycopg2.connect("")
In [3]: cur = cnn.cursor()
In [4]: cur.execute("copy (select 1 as x) to stdout")
----> 1 cur.execute("copy (select 1 as x) to stdout")
ProgrammingError: can't execute COPY TO: use the copy_to() method instead
but:
In [6]: cnn = psycopg2.connect("", async=True)
In [7]: cnn.poll()
Out[7]: 2
In [8]: cnn.poll()
Out[8]: 1
In [9]: cnn.poll()
Out[9]: 0
In [12]: cur.execute("copy (select 1 as x) to stdout")
In [14]: cnn.poll()
^C -- hung
So yes, I'll take a look if there is a way to detect we get in this state. But I'm not sure it's possible, because we might not have received a result yet that tells we are in a state not allowed (in a COPY).
Observation: maybe EnterpriseDB has resources enough to help us debugging and fixing this issue, or maybe even implement async copy?