Hi Chamikara,
What I am suggesting is this. If we get the QoS information stored properly that will enable us to build a definite state after a crash.
e.g. We don't need transport info because RM will handle it by way of re-transmissions.
        ServiceContext and ServiceGroupeContext; IMHO WS-Transaction should handle this.
So if we keep the states of QoS layer then we can avoid this heavy serialization.
Any thoughts?
----- Original Message -----
From: Chamikara Jayalath
To: Jaliya Ekanayake
Cc: sandesha-dev@ws.apache.org ; axis-dev@ws.apache.org
Sent: Sunday, July 30, 2006 10:58 PM
Subject: Re: [AXIS2] [Sandesha2] Saving the message context

Hi Jaliya,

Thats good news. But only the properties will not be anough. There are other things like the state of the options object, transports and callback object that also have to be
serialized. There are also references to the other contexts (serviceContext, serviceGroupContext) from the Message Context and we will not want to loose these connections when the Message Context is deserialized.
However if it can be declared that the referenced contexts will not be serialized when serializing one context, that paves the way for a solution. But not sure weather this is valid for all cases.(Still have to think more on reconstructing the context hierarchy)


On 7/31/06, Jaliya Ekanayake <jnekanayake@gmail.com> wrote:
Hi All,
As far as I remember we spent some time during the design of axis2 to solve this problem. The final conclusion we made was to do our own serialization by serializing only the properties (serializable objects) in the property bag not the entire message context which has pointers to other contexts.
----- Original Message -----
Sent: Sunday, July 30, 2006 8:40 PM
Subject: Re: [AXIS2] [Sandesha2] Saving the message context

Hi Bill,

I agree that doing serialization within context objects is the best approach in a design perspective. The approach I followed was only possible due to MessageContext already having made its useful state public.

I also originally tried to follow Externalizable approach and introduced externalizable methods to all the contexts (they hv now been removed due to not having any usages). The main problem I had in this approach was having to serialize the whole context hierarchy.

Every message context has a pointer to the configurationContext so to be general (not to be specific to our scenario) in the serialization method we would have to serialize this object as well.Since this has pointers to all other contexts they will be serialied too. What I am saying is that when adding the externalizable method to the axis2 codebase we would have to serialize the configContext and other contexts as well (because some people may actually want to serialize the whole context hierarchy). But in our case it seemed like this would be a burden. Every deserialized message context with come up with its own context hierarchy and maching between two deserialized Message contexts will be extremely difficult.

If you find a solution to this problem I agree that your and Anns approach is the best way to go and I would like to use that in my code :-)


On 7/29/06, Bill Nagy < nagy@watson.ibm.com> wrote:
On Fri, 2006-07-28 at 23:46 -0400, Rajith Attapattu wrote:
> Anne,
> Again I will advice again serializing the contexts using any form of
> serialization. This will not scale at all in a production environment.

Hi Rajith,

Could you please explain this last comment?

> Again this approach will be error prone and as chamikara mentioned
> there will be too many information saved in the database.

I don't understand why you and Chamikara keep saying that there will be
too much information serialized.  You have the option of taking complete
control of the serialization, thereby writing/reading only the
information that you want and in the form that you want it to be in.  I
don't believe that Ann is arguing for simply using the default
serialization, only about who should be in control of making the
decisions as to what should be saved.

> I am looking at clustering certain information within the ctx heirachy
> for high availability and I would only do with the bare minimum.
> In my opinion the performance overhead of serializing and
> deserializing (and validations to avoid erros) is a lot more than
> saving the required info in a bean like what chamikara does for
> Sandesha and then reconstructing it.

Having the objects persist their own state is far less error prone than
having a third-party piece of code do the persistence.  For one, anytime
someone changes or adds a piece of information that needs to be saved in
order to correctly restore the state, they have to remember to modify
the external code.  It's generally hard enough to remember to modify
code embedded in the class itself, much less having to remember to
modify a completely separate piece of code.

Secondly, you require the objects that need to be saved to expose
methods, to return the portions that you want to have serialized, that
you may not have to expose otherwise.

In effect, the approach that you've chosen has abandoned encapsulation
and created fragile dependencies -- this is bad design.


> Regards,
> Rajith
> On 7/28/06, Chamikara Jayalath < chamikaramj@gmail.com > wrote:
>         Hi Ann,
>         Yes. We had introduced Externalizable implementaitons for all
>         of the Context hierarchy objects sometime back. But this
>         approach seemed to be saving too much information on the
>         database.
>         For example at some point there may be following context
>         objects available in a running axis2 instance.
>         1. configuration context object
>         2. service group context objects
>         3 service context objects
>         4. Operation context objects
>         5. A lot of message context objects
>         If we try serializing starting from a message context, since
>         we have to serialize every incoming message context all these
>         objects will be serialized every time (recall that the message
>         context hs a link to the configuration context which has links
>         to all other context objects). Think how deficult the
>         reconstruction would be. Every deserialized message context
>         will come up with its own hierarchy of context objects which
>         may not map with the context objects reconstructed by
>         deserializing others message contexts.
>         Thats why I went for this approach of saving only the relavent
>         information. It seemed to be much cleaner and it was
>         working :-)
>         You had mentioned about serializing the AxisOperaion object.
>         All the 'Axis*'  objects in Axis2 (AxisConfiguration,
>         AxisServiceGroupt etc.) contains deployment time information.
>         So we can safely ignore them in the serializing process.
>         Chamikara
>         On 7/29/06, Ann Robinson < robinsona@us.ibm.com> wrote:
>                 Hi Chamikara,
>                 Thanks for the information.
>                 Did you consider using java.io.Externalizable for the
>                 AXIS2 message context-related classes? (Having the
>                 work done by the AXIS2 objects would have simplified
>                 the actions that Sandesha needed to take in order to
>                 save the message context, so I am curious about any
>                 issues that were encountered.
>                 In the MessageStoreBean, how much of the various
>                 objects do you store as Strings? For example, the
>                 AxisOperation object contains several lists and the
>                 executionChain object contains a list of handlers and
>                 phases.
>                 Ann
>                 WebSphere Development, Web Services Engine
>                 IBM
>                 11501 Burnet Rd IZip 9035G021
>                 Austin, TX 78758
>                 (512)838-9438 TL 678-9438
>                 Inactive hide details for Chamikara"Chamikara
>                 Jayalath" < chamikaramj@gmail.com >
>                                                 "Chamikara Jayalath" <chamikaramj@gmail.com >
>                                                 07/28/2006 07:23 AM
>                                                 Please respond to
>                                                 axis-dev@ws.apache.org
>                            To
>                 Ann
>                 Robinson/Austin/IBM@IBMUS
>                            cc
>                 axis-dev@ws.apache.org, sandesha-dev@ws.apache.org
>                       Subject
>                 Re: [AXIS2]
>                 [Sandesha2]
>                 Saving the
>                 message
>                 context
>                 Hi Ann,
>                 I did some work on serializing message contexts and
>                 reconstructing them. This was done as a part of the
>                 Sandesha2 Persistent Storage Manager implementation.
>                 Unfortunately could not commit the code into Apache
>                 due to a license issue (it was dependent on
>                 Hibernate). But will try to host it somewhere else
>                 soon.
>                 The approach i took was extracting the relevant
>                 information from the message context, and saving them
>                 in a java bean. Later this bean was used to recostruct
>                 the message context. The format of this bean was as
>                 follows.
>                 public class MessageStoreBean {
>                 private String SOAPEnvelopeString;
>                 private String storedKey;
>                 private int SOAPVersion = 0;
>                 private String transportOut;
>                 private String axisServiceGroup;
>                 private String axisService;
>                 private String axisOperation;
>                 private String axisOperationMEP;
>                 private String toURL;
>                 private String transportTo;
>                 private int flow;
>                 private String executionChainString;
>                 private String messageReceiverString;
>                 private boolean serverSide;
>                 private String inMessageStoreKey;
>                 private String messageID;
>                 private String persistentPropertyString;
>                 private String callbackClassName;
>                 private String action;
>                 }
>                 As you can see the aim was to avoid Java
>                 serialization. One defect here is SOAP envelope being
>                 saved as a string, which may not be possible in the RM
>                 +MTOM scenario. I guess we can support that when a
>                 better serialization mechanism gets available for SOAP
>                 envelopes.
>                 Chamikara
>                 On 7/27/06, Ann Robinson <robinsona@us.ibm.com >
>                 wrote:
>                         Hi all,
>                         I have posted this note to both the AXIS2 and
>                         SANDESHA developer discussion lists, so I
>                         apologize in advance to those folks who get
>                         multiple copies of this note.
>                         I am investigating how to save and restore the
>                         message context in AXIS2. This is
>                         functionality that would be used by other
>                         quality-of-service layers, for example, by a
>                         WS-ReliableMessaging implementation -
>                         particularly one that is composed with
>                         WS-Security, to save the message in persistent
>                         storage and later resume the message
>                         processing.
>                         The AXIS2 message context is very complex (it
>                         includes references to several complicated
>                         objects) and does not lend itself to the
>                         default java serialization mechanism
>                         (java.io.Serializable). In order to save the
>                         message context, the possible solutions
>                         include the following:
>                         (A) Internal Message Context option
>                         Do a customized serialization using
>                         java.io.Externalizable in the complex objects
>                         and use the default serialization mechanism
>                         (java.io.Serializable) in the simple objects.
>                         - - This keeps the knowledge of the object's
>                         internals in the object and keeps the
>                         responsibility in the object for persisting
>                         and resurrecting its own state.
>                         - - This lets an object have a plugpoint where
>                         needed to manage "user" data. This would apply
>                         to the situation where an object maintains a
>                         set of properties or attributes that are
>                         supplied by users of the object. The plugpoint
>                         would define an interface so that the users of
>                         the object could save their
>                         properties/attributes appropriately.
>                         (B) External Layer option
>                         Put in get/set methods in all of the objects
>                         related to the message context in order to
>                         allow another layer or quality of service
>                         (QoS) to extract sufficient information from
>                         the message context in order to save and
>                         resurrect the information.
>                         - - The simplest form of this technique is
>                         saving just the message (and the message
>                         attachments). However, this means that any
>                         processing on the message has to be re-done
>                         from the beginning.
>                         - - If there is a requirement to maintain the
>                         security context with the message, then the
>                         security layer would need to provide
>                         additional interfaces to allow that message's
>                         security context to be acquired by that other
>                         layer.
>                         (C) Core Plugpoint option
>                         Have a plugpoint in the AXIS2 core that would
>                         provide an interface to capture essential
>                         message context data for saving and restoring
>                         it.
>                         - - This solution would be a compromise
>                         between (A) and (B)
>                         - - This requires knowledge of message context
>                         object-related internals inside of the
>                         plugpoint implementation, which is not good
>                         object oriented design
>                         Any other suggestions or comments?
>                         I understand that there has been a previous
>                         attempt to do this in AXIS2 based on Sandesha
>                         requirements and that this attempt did not
>                         work. I was wondering if anyone remembers what
>                         problems were encountered and what issues
>                         ultimately blocked that solution?
>                         Thanks,
>                         Ann
>                         WebSphere Development, Web Services Engine
>                         IBM
>                         11501 Burnet Rd IZip 9035G021
>                         Austin, TX 78758
>                         (512)838-9438 TL 678-9438

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