11:31 a.m.
Jordi Alvarez [http://community.jboss.org/people/jordi_alvarez] created the discussion
"persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/628586#628586
--------------------------------------------------------------
Hello, I am working for an organization for which we have adopted jBPM as the BPM
solution. We are making use also of Drools
Expert, which results in a nice combination.
We have stateful sessions persisted in a database in order to record the state of
long-time running processes (which are the goal of our
BPM).
In order to make changes to the knowledge-base associated to the stateful sessions that we
have, we always redeploy the whole system (ear application + rules + process definitions).
This is where we have the problem. Depending on the changes performed to the database, the
system is not able to reload the persisted sessions (the change could be for example a
change in the condition of a rule). This results in problems and stack traces similar to
the following one:
[...]
Caused by: java.lang.RuntimeException: Unable to load session snapshot
at
org.drools.persistence.session.JPASessionMarshallingHelper.loadSnapshot(JPASessionMarshallingHelper.java:96)
at
org.drools.persistence.session.SingleSessionCommandService.initKsession(SingleSessionCommandService.java:196)
at
org.drools.persistence.session.SingleSessionCommandService.<init>(SingleSessionCommandService.java:159)
... 95 more
Caused by: java.lang.ClassCastException: org.drools.reteoo.ObjectTypeNode
at org.drools.marshalling.impl.InputMarshaller.readRightTuple(InputMarshaller.java:401)
at org.drools.marshalling.impl.InputMarshaller.readRightTuples(InputMarshaller.java:391)
at org.drools.marshalling.impl.InputMarshaller.readFactHandles(InputMarshaller.java:326)
at org.drools.marshalling.impl.InputMarshaller.readSession(InputMarshaller.java:205)
at org.drools.marshalling.impl.DefaultMarshaller.unmarshall(DefaultMarshaller.java:91)
at
org.drools.persistence.session.JPASessionMarshallingHelper.loadSnapshot(JPASessionMarshallingHelper.java:91)
... 97 more
According to some posts (which mainly relate to drools expert), if we were using the
knowledge agent we could update the already loaded sessions, which would allow to migrate
in-memory sessions from the old database to the new database:
http://drools.46999.n3.nabble.com/Dynamic-updates-of-stateful-sessions-td...
http://drools.46999.n3.nabble.com/Dynamic-updates-of-stateful-sessions-td...
http://stackoverflow.com/questions/4368148/is-it-possible-to-add-a-new-ru...
http://stackoverflow.com/questions/4368148/is-it-possible-to-add-a-new-ru...
Nevertheless, we absolutely need a way to migrate persisted sessions from the old database
to the new one. Even in the situation in which we would allow hot modification of the
knowledge base, we cannot have all the stateful sessions loaded in memory when this would
happen.
Is there any facility provided by Drools Expert/Flow that allows to perform this
operations easily? Is there a way/configuration to
load/save sessions without the need to store/retrieve the rete-tree (and instead
recomputing it), which seems to be the problem for these
situations.
We have already posted this information into drools mailing list; but nobody has answered
yet. Any help is appreciated!
Many thanks in advance,
Jordi Alvarez
###
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6:07 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Maciej Swiderski [http://community.jboss.org/people/swiderski.maciej] created the
discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629114#629114
--------------------------------------------------------------
Have you tried Knowledge Agent? It could monitor resources and recreate the knowledge base
when change is discovered. Maybe that is something that can resolve the issues you're
facing.
Jordi Alvarez wrote:
Nevertheless, we absolutely need a way to migrate persisted sessions from the old
database to the new one. Even in the situation in which we would allow hot modification of
the knowledge base, we cannot have all the stateful sessions loaded in memory when this
would happen.
What you mean by old and new data base?
Cheers
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10:03 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Jordi Alvarez [http://community.jboss.org/people/jordi_alvarez] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629350#629350
--------------------------------------------------------------
Hi Maciej, we have been doing some tests with KnowledgeAgent.
We managed to migrate sessions that are in memory when knowledge base changes.
The problem we are facing is that we are not able to have all sessions in memory when
knowledge base modifications happen. This is not possible since we are working with a lot
of sessions.
So, we need some kind of additional processing to that performed by KnowledgeAgent in
order to update those sessions that are persisted (but not loaded in memory).
We hoped that drools expert provided some facility regarding this point, but I guess the
last sentence from the following paragraph extracted from drools expert documentation
(still valid for recently released 5.3CR1 version) is stating that that kind of facility
will come in future versions:
"The Knowlege Agent provides automatic loading, caching and re-loading of resources
and is configured from a
properties files. The Knowledge Agent can update or rebuild this Knowlege Base as the
resources it uses
are changed. The strategy for this is determined by the configuration given to the
factory, but it is
typically pull-based using regular polling. We hope to add push-based updates and rebuilds
in
future versions."
We are in fact now working in our own custom push solution in which we are loading and
persisting sessions, and using the KnowledgeAgent in order to perform the knowledge base
adaptations and making the sessions aware to those changes.
With respect to old and new knowledge base, I was refering to (a) the knowledge base
before the changes were applied, and (b) the knowledge base after applying the changes.
thanks for your answer!
Jordi Alvarez
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11:39 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Demian Calcaprina [http://community.jboss.org/people/calca] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629391#629391
--------------------------------------------------------------
Jordi,
How did you migrate it? Did you solve the exception? As I am having the same problem
esporadically.
Thanks!
Demian
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5:57 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Jordi Alvarez [http://community.jboss.org/people/jordi_alvarez] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629532#629532
--------------------------------------------------------------
Hi Demian,
we are still working on the solution. In our situation, and at this moment, we are
deploying a new knowledge base every time we perform changes to it. This means that in an
initial time we have KB0, for which some sessions were created; and later, we deploy a
knowledge base KB1 (which is, in fact, an evolution of KB0).
The KnowledgeAgent allowed us to migrate sessions online. That is, loading KB0 sessions
with KB0, and then applying a delta that evolves KB0 into KB1. The sessions associated to
KB0 exhibit then the behaviour corresponding to KB1. We are also able to persist those
sessions.
But we have not succeeded in reloading them after the migration has been performed when
KB1 is loaded from scratch.
After a while investigating in that direction, we have abandoned it, and started working
in other directions (which includes looking into the concrete way drools sessions are
persisted).
So, any useful information regarding migration of persisted sessions will be highly
appreciated.
regards,
Jordi Alvarez
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7:39 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Maciej Swiderski [http://community.jboss.org/people/swiderski.maciej] created the
discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629684#629684
--------------------------------------------------------------
Jordi, Damian, finally I have found some time to test it, I did not want to put this note
without confirming it.
I have pretty same issue what you describe. I built a JBoss AS service (sar) that
encapsulates jBPM5 as process engine which is bound to JNDI so application can simple look
it up or use dependency injection.
So process engine is configured to use Guvnor as knowledge base source and uses knowledge
agent to load it and maintain its changes.
Next there is simple web application with servlet that looks up the process engine from
JNDI and gets a stateful session from it. Process engine is designed to maintain the
sessions in regards to internal ids and application is using its own names for the
sessions, for instance it could be user id that is logged on.
When ever operation is invoked on the session, like start process session is disposed,
meaning persisted to db. Next call will get the session from db and invoke other
operations. What I tested is that I modify processes in Guvnor, next build package and
snapshot and perform the operation from the web application. So the session is loaded
again and the changes are automatically applied to it so it operates on the latest version
of knowledge base.
Let me know if that is what you're trying to achieve?
Cheers
Maciej
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4:45 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Jordi Alvarez [http://community.jboss.org/people/jordi_alvarez] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629795#629795
--------------------------------------------------------------
Hi Maciek, in my case yes, this is what we need.
We are now deploying without the help of guvnor, which was going to be introduced in a
near future. I guess the whole behaviour can also be reproduced without guvnor. After
reading your answer, it is worth advancing in this direction, and see whether the use of
guvnor with packages and snapshots is the direct solution for this problem.
Thanks very much, we will report here the success of our work.
Jordi
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1:54 p.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Demian Calcaprina [http://community.jboss.org/people/calca] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/629929#629929
--------------------------------------------------------------
Hi Maciej. Yes, it is a similar case than mine too. I have (for now, changing it) one
session which I reload everytime I start the app, and I have an agent to rebuild my
knowledge base. From time to time, I am facing a similar exception when loading the
session, which I think it is caused to some changes in kbase:
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at
sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at
org.drools.persistence.jpa.KnowledgeStoreServiceImpl.buildCommanService(KnowledgeStoreServiceImpl.java:88)
... 35 more
Caused by: java.lang.RuntimeException: Unable to load session snapshot
at
org.drools.persistence.SessionMarshallingHelper.loadSnapshot(SessionMarshallingHelper.java:96)
at
org.drools.persistence.SingleSessionCommandService.initKsession(SingleSessionCommandService.java:193)
at
org.drools.persistence.SingleSessionCommandService.<init>(SingleSessionCommandService.java:157)
... 40 more
Caused by: java.lang.NullPointerException
at
org.drools.common.ConcurrentNodeMemories.getNodeMemory(ConcurrentNodeMemories.java:65)
at
org.drools.common.AbstractWorkingMemory.getNodeMemory(AbstractWorkingMemory.java:1035)
at
org.drools.marshalling.impl.InputMarshaller.readFactHandles(InputMarshaller.java:327)
at
org.drools.marshalling.impl.InputMarshaller.readSession(InputMarshaller.java:221)
at
org.drools.marshalling.impl.DefaultMarshaller.unmarshall(DefaultMarshaller.java:92)
at
org.drools.persistence.SessionMarshallingHelper.loadSnapshot(SessionMarshallingHelper.java:91)
... 42 more
Thanks,
Demian
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1:53 p.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Maciej Swiderski [http://community.jboss.org/people/swiderski.maciej] created the
discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/630132#630132
--------------------------------------------------------------
Guys, one question when you construct Knowledge Agent do you set newInstance property to
true or false?
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4:31 a.m.
New subject: [jBPM] - Re: persisted stateful sessions and knowledge base changes
Jordi Alvarez [http://community.jboss.org/people/jordi_alvarez] created the discussion
"Re: persisted stateful sessions and knowledge base changes"
To view the discussion, visit: http://community.jboss.org/message/630191#630191
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Hi Maciej, I have tried it both ways, resulting in error both.
At the present moment we have been working in a workaround in which we have patched the
drools code that loads the session in order to perform a migration from one database to
another. And our first experiments tell us that this is working.
We have separated the load process in two parts: a first in which the first part of the
session is read using the "old" knowledge base. This allows to build the
structure associated to the rete tree correctly in the old knowledge base.
Then, it comes a second part in which a second session is built on the "new"
knowledge base, and the facts of the first session are added to it (we added an activation
filter in order to avoid activations derived from this initial load to be executed). The
the load process continues with the rest of the session information but over this second
session (timers and processes mainly).
This is in fact too tricky, but it has shown to work till the moment, while we explore
further a definitive solution in the line you commented (guvnor, compiled packages,
snaptshots, in combination with the knowledge agent), if possible without performing any
drools patch.
regards,
Jordi
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Maciej Swiderski