InternalClientError: cannot switch to state 12

該 issue 除了 traceback 和指向 Discussion #1068 的連結外，沒有提供 asyncpg 檔案、測試或重現步驟。首先閱讀該討論，並追蹤 stack trace 中顯示的 SQLAlchemy asyncpg pool ping 路徑；只有確定了一個取得共識的原因，並有可重現的修正或回歸測試，才算完成。

Discussed in https://github.com/MagicStack/asyncpg/discussions/1068

^{Originally posted by amacfie-tc August 21, 2023}
I received the following error, does anyone know what it means? In the SQLAlchemy engine, pool_pre_ping is set to True.

asyncpg.exceptions._base.InternalClientError: cannot switch to state 12; another operation (2) is in progress
Traceback (most recent call last):
[...]
    status = (await session.execute(sel_status)).scalar()
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/ext/asyncio/session.py", line 454, in execute
    result = await greenlet_spawn(
             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 190, in greenlet_spawn
    result = context.throw(*sys.exc_info())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 2262, in execute
    return self._execute_internal(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 2134, in _execute_internal
    conn = self._connection_for_bind(bind)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 2001, in _connection_for_bind
    return trans._connection_for_bind(engine, execution_options)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 2, in _connection_for_bind
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/orm/state_changes.py", line 139, in _go
    ret_value = fn(self, *arg, **kw)
                ^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 1126, in _connection_for_bind
    conn = bind.connect()
           ^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/engine/base.py", line 3264, in connect
    return self._connection_cls(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/engine/base.py", line 145, in __init__
    self._dbapi_connection = engine.raw_connection()
                             ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/engine/base.py", line 3288, in raw_connection
    return self.pool.connect()
           ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/pool/base.py", line 452, in connect
    return _ConnectionFairy._checkout(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/pool/base.py", line 1366, in _checkout
    with util.safe_reraise():
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/util/langhelpers.py", line 147, in __exit__
    raise exc_value.with_traceback(exc_tb)
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/pool/base.py", line 1304, in _checkout
    result = pool._dialect._do_ping_w_event(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/engine/default.py", line 708, in _do_ping_w_event
    return self.do_ping(dbapi_connection)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/sqlalchemy/dialects/postgresql/asyncpg.py", line 1117, in do_ping
    dbapi_connection.ping()
asyncpg.exceptions._base.InternalClientError: cannot switch to state 12; another operation (2) is in progress
```</div>