Amila, Paul, I don't think I said that application client should have any logic to manage recovery. I simply said that one of following two has to be done to manage recovery in the client side.
1. There should be a permanent RM agent running in the client side, which manages recovery. 2. RM client should check for crashed sequences whenever it is invoked in the client side, if it find any they should be resumed. In both cases work should be done by the RM client transparently, not by the application client. Chamikara On Tue, Jun 17, 2008 at 10:42 AM, Amila Suriarachchi < [EMAIL PROTECTED]> wrote: > > > On Tue, Jun 17, 2008 at 7:09 PM, Paul Fremantle <[EMAIL PROTECTED]> wrote: > >> Amila >> >> The Mercury design is wrong. >> >> The application client should not be responsible for understanding if >> the system needs to restart. There isn't a single successful messaging >> or transaction system in the world that requires the application to >> incorporate logic to handle recovery. Sandesha2 manages automatic >> recovery and so should Mercury. > > > Here the question is that when a client dies. (i.e. system crashed) how it > automatically restart? > Actually I had a chat with Chamikara regarding this and he told that > sandesha2 also can not > automatically restart. > Chamikara could you please comment on this? > > thanks, > Amila. > >> >> >> Paul >> >> On Tue, Jun 17, 2008 at 2:36 PM, Amila Suriarachchi >> <[EMAIL PROTECTED]> wrote: >> > +1 to add a policy to declare whether a service supports Persistence or >> not. >> > >> > IMO if RM provides persistence then it should happen in both client and >> > server side. >> > But at the client side Application layer has to do some part as well. >> > In Mercury if a client dies when sending a sequence it can be restarted >> by >> > sending a message by setting a property called MercuryResumeSequence to >> > true. >> > But in this case Application client have to check how many messages it >> had >> > send to RM either by keeping a track of messages or by examining the >> Mercury >> > data base store. >> > >> > thanks, >> > Amila. >> > >> > On Tue, Jun 17, 2008 at 6:50 AM, Jaliya Ekanayake < >> [EMAIL PROTECTED]> >> > wrote: >> >> >> >> Hi Paul, >> >> >> >> I agree with the two scenarios you mentioned. >> >> So, if the majority of the use cases for RM are of the above type with >> >> long running communications, then we should stick to the persisted >> >> reliability in every usecase. >> >> Otherwise, I think we'd better keep the client side free from the >> >> mandatory database integration. >> >> >> >> Thanks, >> >> Jaliya >> >> >> >> >> >> ----- Original Message ----- From: "Paul Fremantle" <[EMAIL PROTECTED]> >> >> To: "Jaliya Ekanayake" <[EMAIL PROTECTED]> >> >> Cc: <[email protected]> >> >> Sent: Monday, June 16, 2008 1:05 PM >> >> Subject: Re: Policy or other extensions to indicate persistent >> messaging >> >> >> >> >> >>> Jaliya >> >>> >> >>> I agree that it is the responsibility of the client. But I'm worried >> >>> about two scenarios. >> >>> >> >>> 1) The client crashes and restarts - the server has missing messages >> >>> and without them it cannot deliver the later messages that it has. >> >>> 2) The client crashes and restarts - the server has responses stored, >> >>> ready to send, but the client has lost the sequence state and cannot >> >>> accept the stored messages. >> >>> >> >>> I still think that there is a requirement to ENSURE that a particular >> >>> communication is completely reliable. >> >>> >> >>> Paul >> >>> >> >>> On Mon, Jun 16, 2008 at 5:54 PM, Jaliya Ekanayake < >> [EMAIL PROTECTED]> >> >>> wrote: >> >>>> >> >>>> Hi Paul, >> >>>> >> >>>> Please see my comments below. >> >>>> >> >>>> Thanks, >> >>>> Jaliya >> >>>> ----- Original Message ----- From: "Paul Fremantle" < >> [EMAIL PROTECTED]> >> >>>> To: "Jaliya Ekanayake" <[EMAIL PROTECTED]> >> >>>> Sent: Monday, June 16, 2008 11:40 AM >> >>>> Subject: Re: Policy or other extensions to indicate persistent >> messaging >> >>>> >> >>>> >> >>>>> Jaliya >> >>>>> >> >>>>>> My idea is that the persistence is a feature that the admin can >> turn >> >>>>>> on >> >>>>>> or >> >>>>>> off per service. >> >>>>> >> >>>>> So I agree that it is a good feature to turn it on and off per >> >>>>> service, and that we support today. So for this model, what I am >> >>>>> proposing adding is the ability for the server to advertize that it >> >>>>> supports that. >> >>>>> >> >>>>>> If it is to be per sequence, I think it will over >> >>>>>> complicate the handshakes. >> >>>>> >> >>>>> It will *complicate* the handshakes :) I agree. I think to say it >> >>>>> over-complicates the handshake is a subjective idea. >> >>>>> >> >>>> I agree. >> >>>> >> >>>>>> Also, Sandesha should not impose restrictions to the clients based >> on >> >>>>>> their >> >>>>>> persistence settings. >> >>>>> >> >>>>> I don't agree. WSRM imposes plenty of restrictions on the client and >> >>>>> server. It is perfectly possible for a server to refuse to >> communicate >> >>>>> with a client that does not support RM. With WSRM 1.1 It is possible >> >>>>> for clients to demand that the server creates an association between >> >>>>> the sequence and a security session. >> >>>>> >> >>>>> If the server supports persistence but the client doesn't, then >> there >> >>>>> is no overall guarantee of reliability. So I believe that it ought >> to >> >>>>> be *possible* for a server to send CreateSequenceRefused if it >> >>>>> *requires* persistence and the client cannot provide it. Of course >> >>>>> that should be configured by the server. Similarly the client should >> >>>>> be able to demand (like a mustUnderstand) that the server provides a >> >>>>> persistent capability. >> >>>>> >> >>>>> Why do I want this? Almost every customer I talk to says that WSRM >> >>>>> without persistence is basically pointless. >> >>>> >> >>>> I totally agree with this. Without persistance, I can almost trust >> TCP >> >>>> for >> >>>> the reliability. (not for the multi-transport multi-hop cases) >> >>>> So we need persistance for *real* use cases. >> >>>> >> >>>> The blogging from people >> >>>>> >> >>>>> who believe that WSRM should not support persistence has - in my >> view >> >>>>> - been very harmful to the adoption of the spec. Now the normal >> >>>>> argument is that "you can support persistence if you need it". But >> >>>>> frankly, that is a weak argument, because in a real distributed SOA >> >>>>> you cannot (at the moment) know if there is persistence involved, >> >>>>> except maybe by phoning up the sysadmin at the other end. So if you >> >>>>> require proper persistent reliability then you need a way of >> agreeing >> >>>>> between both parties that it exists. Now WSRM has the perfect model >> >>>>> for this negotiation - the CreateSequence/CSResponse. This ability >> to >> >>>>> negotiate details is perfect for this, and I don't see any problem >> >>>>> extending it to support this. >> >>>>> >> >>>> >> >>>> I agree that the Client should be able to request persistence from a >> >>>> Service, but I still don' t understand why we need the server to >> reject >> >>>> a >> >>>> client if it does not support persistence. >> >>>> Here is a scenario. >> >>>> >> >>>> Say we have two companies A and B that perform some communications >> over >> >>>> snail mail. >> >>>> All the mails received by the company B first go through its mail >> >>>> processing >> >>>> system (MPS) which keeps information on all the mails received, and >> also >> >>>> keeps a copy of them. >> >>>> All the mails sent by the company B also go through the same MPS. >> >>>> >> >>>> Company A is not that sophisticated in its operations. They don't >> simply >> >>>> have a system as above. >> >>>> >> >>>> Now consider the communications that could happen. >> >>>> >> >>>> 1. A sends a mail to B >> >>>> If this reach B, things are fine. >> >>>> If this does not reach B then it is a problem of A. A should keep a >> copy >> >>>> so >> >>>> that it can send it again. >> >>>> >> >>>> >> >>>> 2. B sends a mail to A as a response to A's request >> >>>> If this reach A and processed by A things are fine >> >>>> If this reach A but not processed by A, then B can send it again. (up >> to >> >>>> some number of times) >> >>>> If this does not reach A, B can still send it again. >> >>>> >> >>>> 3. B needs to send a mail to A requesting something. (Now A is the >> >>>> service >> >>>> provider) >> >>>> In this case B can request that A provides the necessary reliability >> to >> >>>> its >> >>>> requests. >> >>>> If A does not support it, B should not proceed. >> >>>> >> >>>> Therefore, IMO the client does not need to have a real persistence to >> >>>> use a >> >>>> service offered with persisted reliability, but it can request this >> >>>> feature >> >>>> from the service. >> >>>> >> >>>> Let me know your thoughts. probably I have missed some use case. >> >>>> >> >>>> Thanks, >> >>>> Jaliya >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> Say, the server supports persistance. In that case, any request sent >> by >> >>>> the >> >>>> client is guranteed to be served. >> >>>> >> >>>> >> >>>> >> >>>> >> >>>> >> >>>>> Paul >> >>>>> >> >>>>> , but we can advertise that we have persistence for this >> >>>>>> >> >>>>>> service. >> >>>>> >> >>>>> >> >>>>>> >> >>>>>> Thanks, >> >>>>>> Jaliya >> >>>>>> >> >>>>>> ----- Original Message ----- From: "Paul Fremantle" < >> [EMAIL PROTECTED]> >> >>>>>> To: "Danushka Menikkumbura" <[EMAIL PROTECTED]> >> >>>>>> Cc: <[email protected]> >> >>>>>> Sent: Monday, June 16, 2008 8:12 AM >> >>>>>> Subject: Re: Policy or other extensions to indicate persistent >> >>>>>> messaging >> >>>>>> >> >>>>>> >> >>>>>>> Danushka >> >>>>>>> >> >>>>>>> I'm not clear I understand your point. >> >>>>>>> >> >>>>>>> Firstly, I was just using AMQP as an example - I didn't mean that >> we >> >>>>>>> wanted to be exactly the same as AMQP or do anything with AMQP. >> >>>>>>> >> >>>>>>> So firstly, in general, I don't believe that Sandesha2 can modify >> the >> >>>>>>> persistence on a sequence by sequence basis - either it is on for >> a >> >>>>>>> service or off. However, logically the sequence *is* the level at >> >>>>>>> which persistence can be defined. So these are the options I see: >> >>>>>>> >> >>>>>>> * The server has persistence set permanently on for a service. It >> >>>>>>> does >> >>>>>>> not demand persistence from the client. It publishes a policy >> saying >> >>>>>>> persistence is optional for the client. It accepts any sequence >> >>>>>>> creation, and persistently stores messages. If the client "asks >> for >> >>>>>>> persistence" during the create sequence, then it says "yes I'm >> >>>>>>> persistent in reply" (by some yet to be determined mechanisms). >> This >> >>>>>>> is how we operate today, except with the addition of the policy >> and >> >>>>>>> the optional information passing during create sequence. >> >>>>>>> >> >>>>>>> * The server has persistence set permanently on for a service. It >> >>>>>>> demands persistence from the client. Therefore it publishes a >> policy >> >>>>>>> saying that client's must be persistent. During the CreateSequence >> >>>>>>> exchange, it can refuse any client that doesn't agree (by some >> >>>>>>> yet-to-be-defined mechanism) to be persistent. This would be a new >> >>>>>>> capability. >> >>>>>>> >> >>>>>>> * The server has some clever ability to turn persistence on or off >> >>>>>>> per-sequence based on the create sequence. In this model, the >> server >> >>>>>>> picks up the preference from the client. So the same service might >> >>>>>>> have some persistent and some non-persistent sequences. Maybe this >> is >> >>>>>>> overkill and beyond the basic requirements. I'm not clear. >> However, >> >>>>>>> this seems to be a model that other systems allow. Of course, a >> >>>>>>> server >> >>>>>>> could respond that it doesn't support this capability. >> >>>>>>> >> >>>>>>> Ideally, all of this would be designed to allow backwards >> >>>>>>> compatibility. So even in the cases where the server refuses a >> >>>>>>> sequence because it requires persistence and the client doesn't >> >>>>>>> support this extension, the failure is explained in the error and >> the >> >>>>>>> administrator can see why. >> >>>>>>> >> >>>>>>> Paul >> >>>>>>> >> >>>>>>> On Mon, Jun 16, 2008 at 12:20 PM, Danushka Menikkumbura >> >>>>>>> <[EMAIL PROTECTED]> wrote: >> >>>>>>>> >> >>>>>>>>>>> 1) A policy element to indicate whether this endpoint supports >> >>>>>>>>>>> and/or >> >>>>>>>>>>> requires persistence >> >>>>>>>>>>> >> >>>>>>>>>>> >> >>>>>>>>>> >> >>>>>>>>>> (b) Even if we go for transport level persistence, the endpoint >> >>>>>>>>>> does >> >>>>>>>>>> not >> >>>>>>>>>> have a say in it, because in AMQP we can have either queue >> level >> >>>>>>>>>> persistence >> >>>>>>>>>> (i.e. transport receiver level abstraction) or message level >> >>>>>>>>>> persistence >> >>>>>>>>>> (i.e. message sender level abstraction). >> >>>>>>>>>> >> >>>>>>>> >> >>>>>>>> Hi Paul, >> >>>>>>>> But still this is not doable with AMQP. >> >>>>>>>> >> >>>>>>>> Danushka >> >>>>>>>> >> >>>>>>>> >> >>>>>>> >> >>>>>>> >> >>>>>>> >> >>>>>>> -- >> >>>>>>> Paul Fremantle >> >>>>>>> Co-Founder and CTO, WSO2 >> >>>>>>> Apache Synapse PMC Chair >> >>>>>>> OASIS WS-RX TC Co-chair >> >>>>>>> >> >>>>>>> blog: http://pzf.fremantle.org >> >>>>>>> [EMAIL PROTECTED] >> >>>>>>> >> >>>>>>> "Oxygenating the Web Service Platform", www.wso2.com >> >>>>>>> >> >>>>>>> >> --------------------------------------------------------------------- >> >>>>>>> To unsubscribe, e-mail: [EMAIL PROTECTED] >> >>>>>>> For additional commands, e-mail: [EMAIL PROTECTED] >> >>>>>>> >> >>>>>> >> >>>>>> >> >>>>> >> >>>>> >> >>>>> >> >>>>> -- >> >>>>> Paul Fremantle >> >>>>> Co-Founder and CTO, WSO2 >> >>>>> Apache Synapse PMC Chair >> >>>>> OASIS WS-RX TC Co-chair >> >>>>> >> >>>>> blog: http://pzf.fremantle.org >> >>>>> [EMAIL PROTECTED] >> >>>>> >> >>>>> "Oxygenating the Web Service Platform", www.wso2.com >> >>>> >> >>>> >> >>> >> >>> >> >>> >> >>> -- >> >>> Paul Fremantle >> >>> Co-Founder and CTO, WSO2 >> >>> Apache Synapse PMC Chair >> >>> OASIS WS-RX TC Co-chair >> >>> >> >>> blog: http://pzf.fremantle.org >> >>> [EMAIL PROTECTED] >> >>> >> >>> "Oxygenating the Web Service Platform", www.wso2.com >> >>> >> >>> --------------------------------------------------------------------- >> >>> To unsubscribe, e-mail: [EMAIL PROTECTED] >> >>> For additional commands, e-mail: [EMAIL PROTECTED] >> >>> >> >> >> >> >> >> --------------------------------------------------------------------- >> >> To unsubscribe, e-mail: [EMAIL PROTECTED] >> >> For additional commands, e-mail: [EMAIL PROTECTED] >> >> >> > >> > >> > >> > -- >> > Amila Suriarachchi, >> > WSO2 Inc. >> >> >> >> -- >> Paul Fremantle >> Co-Founder and CTO, WSO2 >> Apache Synapse PMC Chair >> OASIS WS-RX TC Co-chair >> >> blog: http://pzf.fremantle.org >> [EMAIL PROTECTED] >> >> "Oxygenating the Web Service Platform", www.wso2.com >> > > > > -- > Amila Suriarachchi, > WSO2 Inc.
