Infinite hang on leaving conn.transaction() block

Hi, I am experiencing hangs at aexit of Transaction context manager, with traceback as follows:

...
  File "/usr/local/lib/python3.7/dist-packages/asyncpg/transaction.py", line 89, in __aexit__
    await self.__rollback()
  File "/usr/local/lib/python3.7/dist-packages/asyncpg/transaction.py", line 198, in __rollback
    await self._connection.execute(query)
  File "/code/callmeback/detail/log_helpers/postgre_conn.py", line 53, in execute
    return await super(LoggingConn, self).execute(query, *args, timeout=timeout)
  File "/usr/local/lib/python3.7/dist-packages/asyncpg/connection.py", line 273, in execute
    return await self._protocol.query(query, timeout)

Default command timeout is set for connection:

>>> conn = frame.f_locals['self']
>>> conn._config
ConnectionConfiguration(command_timeout=10.0, statement_cache_size=100, max_cached_statement_lifetime=300, max_cacheable_statement_size=15360)
>>> conn._protocol._get_timeout(None)
10.0

So I expect self._protocol.query() to throw TimeoutError of some kind, but related coroutine hanged for three days with no progress.

I will happily provide you with any additional information, if I can. My app has aiomonitor onboard, so if any info reachable that way will help you - please let me know.

I tried to fiddle with conn._protocol, but almost nothing of its state is reachable from aioconsole since it's Cython.

My suspection is that exception that leads to rollback is coming from in-transaction query that somehow leads connection in such a state that rollback() cannot be processed normally. I will provide you with information about exception once that problem triggers next time.

• asyncpg version: 0.18.3
• PostgreSQL version: 10.7
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?:
• Python version: 3.7
• Platform: Ubuntu 16.04
• Do you use pgbouncer?: Yes (session-level pooling)
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: --
• Can the issue be reproduced under both asyncio and
  uvloop?: Yes, I am using uvloop

asyncpg/transaction.py の aexit と rollback から始め、次に connection.py の execute() をたどって _protocol.query() まで確認してください。可能であれば、PostgreSQL 10.7、セッションレベルの pgbouncer プーリング、uvloop を使ってハングを再現します。ロールバックパスが完了するか、ハングする代わりに設定されたタイムアウトを表面化すれば完了です。