[mod_python] Session Hanging Problems

David Lenwell dlenwell at gmail.com
Mon Nov 26 14:50:08 EST 2007

I did .. and then it stopped and I can't explain why .. our software  
is in alpha right now until I finish our custom session solution .. we  
won't go into production until I have this handled.  I messed with  
file permission, forcing different file dbm file names .. it  
eventually works but like you said it hangs for about 4 minutes with  
no explanation.

The database load is fine if you set it up right.. We played with  
running a separate version of mysql cluster across all our web servers  
since it keeps its data in memory, its pretty fast but I think we are  
transitioning to a shared memcache solution .. its all still in the  
air really until I can make something rock solid .. downtime isn't  
really an option.

On Nov 26, 2007, at 11:29 AM, Harish Agarwal wrote:

> Did you also have problems with _apache._global_lock?  For now, I'm  
> not too worried about the database load (if necessary we can  
> transition to an in memory session handler as well), I'd just like  
> to understand the source of the problems as I have a feeling this  
> problem will always show up (as the other David has noticed this  
> problem with FileSession as well) as long as we're inheriting our  
> session handler from BaseSession.
> Thanks,
> Harish
> On Nov 26, 2007, at 11:21 AM, David Lenwell wrote:
>> yeah .. its very broken for me too .. What I am working on is my  
>> own session handler.. I don't feel that mysql is a valid  
>> replacement because it puts unnecessary load on your database server.
>> We are debating on open sourcing the code I am working on. if I win  
>> the argument that open source can be good for us then I will  
>> contribute my code to the project.
>> On Nov 26, 2007, at 10:55 AM, David Janes wrote:
>>> All I can say is "we too" -- we're using FileSession. We have not  
>>> been
>>> able to come up with a cure, though we've minimized use of sessions
>>> which brings the frequency down significantly.
>>> Regards, etc...
>>> David
>>> On Nov 26, 2007 1:39 PM, Harish Agarwal <harish at octopart.com> wrote:
>>>> I'm using session handling with ModPython 3.3.1.  Originally I was
>>>> using DbmSession and have since transitioned to a custom MySQL  
>>>> Session
>>>> handler.  With both session types, however, I've noticed that  
>>>> session
>>>> initialization intermittently hangs (not forever, but takes as  
>>>> long as
>>>> four minutes to complete), at a low-ish (a handful of times every
>>>> hour, while receiving, say, on order of a thousand or so requests
>>>> every hour) frequency which seems to scale with the amount of  
>>>> traffic
>>>> we're receiving.  I had read that long DbmSession cleanups can  
>>>> cause
>>>> problems, which is why I transitioned to the MySQL system, which  
>>>> takes
>>>> < 1 second to complete, but I'm still noticing the long session  
>>>> init
>>>> times.
>>>> I put some debugging statements into the code and it seems to be
>>>> related to session locking.  In particular, it is this function  
>>>> call
>>>> in the lock method of the BaseSession class:
>>>> _apache._global_lock(self._req.server, self._sid)
>>>> which is taking some time to complete. I'm not familiar with
>>>> _apache._global_lock (is it used to apply a mutex lock to the
>>>> session?) and am having trouble finding information describing its
>>>> usage - but it seems likely that this is the root cause.  In the  
>>>> past
>>>> I've had problems with session locking but have since  
>>>> transitioned the
>>>> code to ensure that only one session is created per request, as  
>>>> such:
>>>> if not hasattr(req,'session'):
>>>>           req.session = Session.MySQLSession(req)
>>>> Can anyone tell me if this kind of behavior is normal or is  
>>>> indicative
>>>> of some common configuration or coding error?  Any help would be
>>>> greatly appreciated.
>>>> Thanks,
>>>> -Harish
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>>> -- 
>>> David Janes
>>> Founder, BlogMatrix
>>> http://www.blogmatrix.com
>>> http://blogmatrix.blogmatrix.com
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