QueuePool negative overflow
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davep...@googlemail.com
Jun 27, 2016, 10:48:58 AM6/27/16
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Hi
>>> engine.pool.status()
'Pool size: 20 Connections in pool: 19 Current Overflow: -36 Current Checked out connections: -35'
Does anyone know of any scenarios that could cause this?
QueuePool.status() is returning some odd looking negative values from one of our production applications.
'Pool size: 20 Connections in pool: 19 Current Overflow: -36 Current Checked out connections: -35'
The pool was initialised with: pool_size=20, max_overflow=100.
Does anyone know of any scenarios that could cause this?
We are using SQLAlchemy==1.0.13 connecting to MySql 5.6.
The application runs in a single python process that uses eventlet to manage many greenthreads.
The situation appears to occur sometime after the overflow has been used.
Thanks
Mike Bayer
Jun 27, 2016, 11:21:39 AM6/27/16
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On 06/27/2016 10:48 AM, davepuffin via sqlalchemy wrote:
> Hi
>
> QueuePool.status() is returning some odd looking negative values from
> one of our production applications.
>
>>>> engine.pool.status()
> 'Pool size: 20 Connections in pool: 19 Current Overflow: -36 Current
> Checked out connections: -35'
>
> The pool was initialised with: pool_size=20, max_overflow=100.
>
>
> Does anyone know of any scenarios that could cause this?
>
>
> We are using SQLAlchemy==1.0.13 connecting to MySql 5.6.
> The application runs in a single python process that uses eventlet to
> manage many greenthreads.
/ Lock primitives before importing SQLAlchemy? QueuePool relies upon
traditional thread and locking primitives which will fail if you use
them unpatched in a green-thread situation. The Queue here is
basically Python's Queue.Queue so it appears like the queue has been
populated with more objects than it is supposed to allow.
>
> The situation appears to occur sometime after the overflow has been used.
>
> Thanks
>
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Dave Puffin
Jun 27, 2016, 11:30:21 AM6/27/16
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Thanks for the reply :)
I think you're right in that it must be threading related somehow, but it looks like all the monkeypatching has been applied correctly. If I examine the locking object used in the pool I get:
>>> type(engine.pool._overflow_lock)
<class 'eventlet.semaphore.Semaphore'>
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Mike Bayer
Jun 27, 2016, 11:36:21 AM6/27/16
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Well it is possible QueuePool doesn't do the right thing under eventlet,
though we use it a lot w/ eventlet in Openstack and I've tested it
myself quite a bit. Have not peeked at this number, however.
You'd need to produce for me a self contained test suite that
illustrates this behavior occurring, that would be very helpful in order
to track this down.
Do you see too many actual database connections in play when this
condition occurs ? That is, using netstat you'd see more than 120
connections.
> <mailto:sqlalchemy%2Bunsu...@googlegroups.com>
> <mailto:sqlalchemy+...@googlegroups.com
> <mailto:sqlalchemy%2Bunsu...@googlegroups.com>>.
though we use it a lot w/ eventlet in Openstack and I've tested it
myself quite a bit. Have not peeked at this number, however.
You'd need to produce for me a self contained test suite that
illustrates this behavior occurring, that would be very helpful in order
to track this down.
Do you see too many actual database connections in play when this
condition occurs ? That is, using netstat you'd see more than 120
connections.
> <mailto:sqlalchemy+...@googlegroups.com
> <mailto:sqlalchemy%2Bunsu...@googlegroups.com>>.
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>
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davep...@googlemail.com
Jun 27, 2016, 12:46:23 PM6/27/16
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I've checked netstat and there are only 15 mysql connections (status is still reporting the same):
Pool size: 20 Connections in pool: 19 Current Overflow: -36 Current
Checked out connections: -35
Checked out connections: -35
On our other servers, the number of connections (from netstat) matches up with the pool status as expected.
I will try and recreate the problem with a test.
Many thanks!
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Mike Bayer
Jun 27, 2016, 2:05:14 PM6/27/16
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On 06/27/2016 12:46 PM, davepuffin via sqlalchemy wrote:
> I've checked netstat and there are only 15 mysql connections (status is
> still reporting the same):
> Pool size: 20 Connections in pool: 19 Current Overflow: -36 Current
> Checked out connections: -35
>
> On our other servers, the number of connections (from netstat) matches
> up with the pool status as expected.
> I will try and recreate the problem with a test.
>
> Many thanks!
>
>
>
> On Monday, June 27, 2016 at 4:36:21 PM UTC+1, Mike Bayer wrote:
>
> Well it is possible QueuePool doesn't do the right thing under
> eventlet,
> though we use it a lot w/ eventlet in Openstack and I've tested it
> myself quite a bit. Have not peeked at this number, however.
>
> You'd need to produce for me a self contained test suite that
> illustrates this behavior occurring, that would be very helpful in
> order
> to track this down.
>
> Do you see too many actual database connections in play when this
> condition occurs ? That is, using netstat you'd see more than 120
> connections.
>
>
>
> On 06/27/2016 11:30 AM, 'Dave Puffin' via sqlalchemy wrote:
> > Thanks for the reply :)
> >
> > I think you're right in that it must be threading related somehow,
> but
> > it looks like all the monkeypatching has been applied correctly. If I
> > examine the locking object used in the pool I get:
> >
> >>>> type(engine.pool._overflow_lock)
> >
> > <class 'eventlet.semaphore.Semaphore'>
> >
> >
> > On Mon, Jun 27, 2016 at 4:21 PM, Mike Bayer
> > <mailto:sqlalchemy%2Bunsu...@googlegroups.com
> <javascript:>>
> > <mailto:sqlalchemy+...@googlegroups.com <javascript:>
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