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Best Practice for Transient Sessions?

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Joshua Kramer

Best Practice for Transient Sessions?

Hello,

Is there a best practice for handling transient sessions - where server
and local queues are created, publish and consume one message, then
destroyed?

I'm thinking of a case where I service web pages. If I keep the same
queues alive between transactions, then it is concievable that one persons
web page could display data from the previous transaction - if that
transaction is canceled before it receives a response, then the subsequent
transaction will receive an invalid response. If I key the transactions,
I can reject invalid transactions.

Thoughts?

I'm looking into the capabilities of my web framework (Django) to handle
persistent objects.

Thanks,
-Josh

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Justin Ross-2

Re: Best Practice for Transient Sessions?

Hi, Josh.

Do you have some kind of user session id you could use to create session-scoped queues? With a queue per active user, the world would remain coherent without the need to create and destroy things too much.

Justin

-------- Original Message --------
Subject: Best Practice for Transient Sessions?
Date: Wed, 28 Jan 2009 11:05:00 -0500 (EST)
From: Joshua Kramer <[hidden email]>
Reply-To: [hidden email]
To: [hidden email]

Hello,

Is there a best practice for handling transient sessions - where server
and local queues are created, publish and consume one message, then
destroyed?

I'm thinking of a case where I service web pages. If I keep the same
queues alive between transactions, then it is concievable that one persons
web page could display data from the previous transaction - if that
transaction is canceled before it receives a response, then the subsequent
transaction will receive an invalid response. If I key the transactions,
I can reject invalid transactions.

Thoughts?

I'm looking into the capabilities of my web framework (Django) to handle
persistent objects.

Thanks,
-Josh

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Alan Conway

Re: Best Practice for Transient Sessions?

Justin Ross wrote:
> Hi, Josh.
>
> Do you have some kind of user session id you could use to create session-scoped queues? With a queue per active user, the world would remain coherent without the need to create and destroy things too much.
>

Josh - if you create sessions without explcitly giving them a name, qpid will generate a UUID as the name.
You can get it with session.getId().getName()

Of course if you have your own unique session identifier you can use that instead.

> Justin
>
> -------- Original Message --------
> Subject: Best Practice for Transient Sessions?
> Date: Wed, 28 Jan 2009 11:05:00 -0500 (EST)
> From: Joshua Kramer <[hidden email]>
> Reply-To: [hidden email]
> To: [hidden email]
>
> Hello,
>
> Is there a best practice for handling transient sessions - where server
> and local queues are created, publish and consume one message, then
> destroyed?
>
> I'm thinking of a case where I service web pages. If I keep the same
> queues alive between transactions, then it is concievable that one persons
> web page could display data from the previous transaction - if that
> transaction is canceled before it receives a response, then the subsequent
> transaction will receive an invalid response. If I key the transactions,
> I can reject invalid transactions.
>
> Thoughts?
>
> I'm looking into the capabilities of my web framework (Django) to handle
> persistent objects.
>
> Thanks,
> -Josh
>

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Jonathan Robie

Re: Best Practice for Transient Sessions?

Alan Conway wrote:
> Justin Ross wrote:
>> Hi, Josh.
>> Do you have some kind of user session id you could use to create
>> session-scoped queues? With a queue per active user, the world would
>> remain coherent without the need to create and destroy things too much.
>
> Josh - if you create sessions without explcitly giving them a name,
> qpid will generate a UUID as the name.
> You can get it with session.getId().getName()

The request-response example does just this. In the C++ flavor:

stringstream response_queue;
response_queue << "client" << session.getId().getName();

session.queueDeclare(arg::queue=response_queue.str());
session.exchangeBind(arg::exchange="amq.direct",
arg::queue=response_queue.str(), arg::bindingKey=response_queue.str());

Remember to delete the queue when you're done with it, or queues will
accumulate on the server.

But if you want a user's queue to persist on the server, save an
identifier in a cookie or some other place.

Jonathan

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Joshua Kramer

Re: Best Practice for Transient Sessions?

> Remember to delete the queue when you're done with it, or queues will
> accumulate on the server.

In python - is it enough to call the close() method of the queue object,
or is there also some sort of destroy() method?

Thanks,
-Josh

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Rafael Schloming

Re: Best Practice for Transient Sessions?

Joshua Kramer wrote:
>
>> Remember to delete the queue when you're done with it, or queues will
>> accumulate on the server.
>
> In python - is it enough to call the close() method of the queue object,
> or is there also some sort of destroy() method?

Calling the close() method of the queue object does NOT delete the queue
on the server. You can use the queue_delete(...) method for that.

--Rafael

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Alan Conway

Re: Best Practice for Transient Sessions?

Rafael Schloming wrote:

> Joshua Kramer wrote:
>>
>>> Remember to delete the queue when you're done with it, or queues will
>>> accumulate on the server.
>>
>> In python - is it enough to call the close() method of the queue
>> object, or is there also some sort of destroy() method?
>
> Calling the close() method of the queue object does NOT delete the queue
> on the server. You can use the queue_delete(...) method for that.
>
> --Rafael

you can also declare the queue with auto_delete=true if you want it automatically deleted
when you close your session

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Jonathan Robie

Re: Best Practice for Transient Sessions?

In reply to this post by Joshua Kramer

Joshua Kramer wrote:
>
>> Remember to delete the queue when you're done with it, or queues will
>> accumulate on the server.
>
> In python - is it enough to call the close() method of the queue
> object, or is there also some sort of destroy() method?
qpid.session.Session.queueDelete() is your friend. I will be posting
API docs for Python on the Qpid site today or tomorrow, but here's
the method you are looking for.

Jonathan

delete a queue

This command deletes a queue. When a queue is deleted any pending
messages are sent to the alternate-exchange if defined, or discarded
if it is not.

queue

Specifies the name of the queue to delete.

if_unused -- delete only if unused

If set, the server will only delete the queue if it has no
consumers. If the queue has consumers the server does does not
delete it but raises an exception instead.

if_empty -- delete only if empty

If set, the server will only delete the queue if it has no
messages.

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Jonathan Robie

Re: Best Practice for Transient Sessions?

In reply to this post by Alan Conway

Alan Conway wrote:
> you can also declare the queue with auto_delete=true if you want it
> automatically deleted
> when you close your session

And that's more robust - it does not depend on your program to get it
right, and it works even if your program crashes.

Jonathan

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Jonathan Robie

Python API docs posted

In reply to this post by Joshua Kramer

I just posted Python API docs here:

http://people.apache.org/~jonathan/qpid/api/python/html/

I'll be linking to that form the wiki. I've decided I'm a fan of epydoc ;->

Jonathan

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Carl Trieloff

Re: Python API docs posted

Jonathan Robie wrote:

> I just posted Python API docs here:
>
> http://people.apache.org/~jonathan/qpid/api/python/html/
>
> I'll be linking to that form the wiki. I've decided I'm a fan of
> epydoc ;->
>
> Jonathan
>
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>

don't post it in your home, dir let put it under docs section. I can
help you

Carl.

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Jonathan Robie

Re: Python API docs posted

Carl Trieloff wrote:
> don't post it in your home, dir let put it under docs section. I can
> help you
OK - thanks, see you in IRC!

Jonathan

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Ted Ross

Re: Python API docs posted

In reply to this post by Jonathan Robie

Jonathan Robie wrote:

Jonathan,

Can you remove references to the management and managementdata modules?
These are obsolete.

Thanks,

-Ted

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Jonathan Robie

Re: Python API docs posted

Ted Ross wrote:
> Can you remove references to the management and managementdata
> modules? These are obsolete.

Eventually, but ....

There are actually a zillion obsolete things in the generated API docs,
which makes them a bit of a trap. It needs major cleaning, either by
cleaning up the API itself (the better way?) or by maintaining a list
over time of which parts of the API are there only for historical purposes.

Not sure how to proceed on this. But doing this for just two modules
probably isn't best.

Jonathan

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Joshua Kramer

Re: Best Practice for Transient Sessions?

In reply to this post by Alan Conway

On Wed, 28 Jan 2009, Alan Conway wrote:

> you can also declare the queue with auto_delete=true if you want it
> automatically deleted
> when you close your session

What about the local queues generated by session.incoming(), such as:

locLocalQueue = session.incoming(locLocalQueueName, auto_delete=True)

Obviously auto_delete doesn't work here - but are these queues discarded
when the session is closed?

Thanks!
-Josh

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Carl Trieloff

Re: Best Practice for Transient Sessions?

> Obviously auto_delete doesn't work here - but are these queues
> discarded when the session is closed?
>

yes, when the session closes

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