[Sqlalchemy-tickets] Issue #3527: Possible Connection Leak? (zzzeek/sqlalchemy)

[Tim M. <iss...@bi...>]

New issue 3527: Possible Connection Leak?
https://bitbucket.org/zzzeek/sqlalchemy/issues/3527/possible-connection-leak

Tim Mitchell:

SQLA 1.0.8
I am trying to debug an inexplicable 'connection unexpectedly closed' error when I run a test suite (with lots of engine.dispose()s).  When I came across this.

Given a pretty normal query in a ThreadLocal session and a QueuePool
```
#!python

with db_context() as session:
        session.query(tables.Attachment).get(attachment_id)

```
When I look at the callstack for a new connection I see this:

```
#!python

...
Query._connection_from_session(..., close_with_result=True)
Session._connection_for_bind(..., kw={close_with_result=True))
SessionTransaction._connection_for_bind(...)  # close_with_result NOT passed
Engine.contextual_connect(..., close_with_result=False)
...
# Create DBAPI connection
```

Specifying a NullPool makes everything work fine.