On Tue, May 12, 2015 at 9:28 AM, Mike Bayer <mike...@zzzcomputing.com>
wrote:
>
>
> On 5/12/15 9:34 AM, Jonathon Nelson wrote:
>
> I'm working on an application where I want to use one and only one
> connection, even in the face of errors.
> Originally I used AssertionPool, but it seemed to misbehave sometimes in
> the face of a disconnection.
> Switching to QueuePool, I somewhat surprisingly got the same result.
>
> This is how I perform my test. Using the code below, I start it with a URI
> and wait for it to tell me to stop postgresql, which I then do.
> I hit enter, and get an (expected) error as it fails to connect.
> When I hit enter a second time, I get an *unexpected* traceback, a
> different one for QueuePool as for AssertionPool, but unexpected
> nonetheless.
>
> it would be super helpful if you could share what this traceback is.
>
Sure. Below find *two* runs (split on '*****************'), the first being
the one with AssertionPool and the latter with QueuePool.
*****************
Now stop PG.
-=>
Got an (expected) error: (psycopg2.OperationalError) could not connect to
server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket
"/var/run/postgresql/.s.PGSQL.5432"?
-=!
No handlers could be found for logger "sqlalchemy.pool.AssertionPool"
Traceback (most recent call last):
File "t3.py", line 48, in <module>
main()
File "t3.py", line 36, in main
with engine.begin() as conn:
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
1903, in begin
conn = self.contextual_connect(close_with_result=close_with_result)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
2034, in contextual_connect
self._wrap_pool_connect(self.pool.connect, None),
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
2069, in _wrap_pool_connect
return fn()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 376,
in connect
return _ConnectionFairy._checkout(self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 708,
in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 480,
in checkout
rec = pool._do_get()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 1257,
in _do_get
raise AssertionError("connection is already checked out" + suffix)
AssertionError: connection is already checked out at:
File "t3.py", line 48, in <module>
main()
File "t3.py", line 26, in main
with engine.begin() as conn:
*****************
Now stop PG.
-=>
Got an (expected) error: (psycopg2.OperationalError) could not connect to
server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket
"/var/run/postgresql/.s.PGSQL.5432"?
-=!
No handlers could be found for logger "sqlalchemy.pool.QueuePool"
Traceback (most recent call last):
File "t3.py", line 48, in <module>
main()
File "t3.py", line 36, in main
with engine.begin() as conn:
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
1903, in begin
conn = self.contextual_connect(close_with_result=close_with_result)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
2034, in contextual_connect
self._wrap_pool_connect(self.pool.connect, None),
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line
2069, in _wrap_pool_connect
return fn()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 376,
in connect
return _ConnectionFairy._checkout(self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 708,
in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 480,
in checkout
rec = pool._do_get()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 1042,
in _do_get
(self.size(), self.overflow(), self._timeout))
sqlalchemy.exc.TimeoutError: QueuePool limit of size 1 overflow 0 reached,
connection timed out, timeout 0
*****************
I hope this is helpful.
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