[wildfly-dev] The EJB client and remote JTA transaction propagation
Tom Jenkinson
tom.jenkinson at redhat.com
Tue Feb 9 12:07:58 EST 2016
I understood what you said but didn't communicate my suggestion clearly
enough sorry.
System1 creates a new transaction
System1 registers a synchronization SYNC1 on transaction to record soon to
be pending request for System2 *** NEW BIT
System1 invokes EJB1 on System2 with XID1
System2 examines EJB1's transaction mode
System2 inflows XID1
System2 executes EJB1
System2 returns with "EnlistMe" flag
System1 updates SYNC1 to say the call returned *** NEW BIT
System1 enlists System2
...other work happens...
System1 prepares XID1
System2 prepares XID1 & returns XA_OK
System1 commits
System2 commits
If the failure happens before EJB1 returns then SYNC1 throws an exception
during beforeCompletion.
On 9 February 2016 at 16:50, David M. Lloyd <david.lloyd at redhat.com> wrote:
> I think you misunderstood what I"m getting at. Consider this normal
> sequence of events under the proposed enlistment strategy:
>
> System1 creates a new transaction
> System1 invokes EJB1 on System2 with XID1
> System2 examines EJB1's transaction mode
> System2 inflows XID1
> System2 executes EJB1
> System2 returns with "EnlistMe" flag
> System1 enlists System2
> ...other work happens...
> System1 prepares XID1
> System2 prepares XID1 & returns XA_OK
> System1 commits
> System2 commits
>
> Now what happens if the System1-System2 connection is broken before EJB1
> returns? System2 is never enlisted, System1 may prepare & commit the XID1
> transaction without ever knowing about System2, which now has an orphaned
> transaction which has performed some unknown amount of work under the same
> GTID as the now-committed transaction. System2's transaction times out,
> the work is rolled back, and chaos ensues.
>
> So this means that I have to have System2 tell System1 to enlist *before*
> "System2 executes EJB1" rather than after, right?
>
>
> On 02/09/2016 10:41 AM, Tom Jenkinson wrote:
>
>> My understanding would be that the EJB transport would detect the
>> transaction.commit call (although it should have an outstanding EJB call
>> so
>> I don't think that it would be possible for a client to call commit) and
>> throw an exception. It could be that EJB transport would register a
>> synchronization beforeCompletion to do this.
>>
>> On 9 February 2016 at 14:41, David M. Lloyd <david.lloyd at redhat.com>
>> wrote:
>>
>> I have a follow-up question about delaying enlistment (I'm getting to this
>>> point in the code).
>>>
>>> I'm worried about a scenario wherein the subordinate server begins the
>>> transaction, does some work in the EJB, and then tries to return, but the
>>> connection to the server has been partitioned indefinitely. The server
>>> *may* opt to continue and commit the transaction despite the subordinate
>>> failure, in which case the subordinate, not receiving any control
>>> messages
>>> from the root coordinator, would roll back the transaction at the
>>> timeout,
>>> while the server (not knowing about the subordinate server) would
>>> continue
>>> and commit the transaction, not knowing what work (if any) the
>>> subordinate
>>> server had performed.
>>>
>>> Is this a real problem? Perhaps I do need an "enlist me" callback to the
>>> server after all, which executes before the EJB imports and resumes the
>>> subordinate transaction?
>>>
>>>
>>> On 02/02/2016 08:27 AM, Tom Jenkinson wrote:
>>>
>>> No problem :)
>>>>
>>>> On 2 February 2016 at 13:49, David M. Lloyd <david.lloyd at redhat.com>
>>>> wrote:
>>>>
>>>> Ah okay, cool. This is an easy (and, in hindsight, rather obvious)
>>>>
>>>>> enhancement that I can build into the new protocol with a minimum of
>>>>> effort.
>>>>>
>>>>> Thanks!
>>>>>
>>>>> On 02/02/2016 03:01 AM, Tom Jenkinson wrote:
>>>>>
>>>>> Hi David,
>>>>>
>>>>>>
>>>>>> I was referring to case 1 when the transaction is inflowed into a
>>>>>> second
>>>>>> server. For JTS the type of transaction we create is a
>>>>>> ServerTopLevelAction and this in its ctor calls back to the remote
>>>>>> server:
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://github.com/jbosstm/narayana/blob/master/ArjunaJTS/jts/classes/com/arjuna/ats/internal/jts/orbspecific/interposition/resources/arjuna/ServerTopLevelAction.java#L121
>>>>>> If the transport can do that without the TMs assistance then that
>>>>>> works
>>>>>> for me :)
>>>>>>
>>>>>> I don't think we should optimize for case 2. The incidents where a
>>>>>> transaction is created and not used should be really low.
>>>>>>
>>>>>> Thanks,
>>>>>> Tom
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 1 February 2016 at 15:43, David M. Lloyd <david.lloyd at redhat.com
>>>>>> <mailto:david.lloyd at redhat.com>> wrote:
>>>>>>
>>>>>> I was thinking about this a bit. It seems to me that there are
>>>>>> two
>>>>>> "levels" of this that could be explored:
>>>>>>
>>>>>> 1. A transaction was made available to the server, but the EJB
>>>>>> on
>>>>>> the server does not use the caller's transaction context, so the
>>>>>> EJB
>>>>>> code never actually has to inflow the transaction. The EJB code
>>>>>> would be able to make this determination without any help from
>>>>>> the
>>>>>> TM.
>>>>>>
>>>>>> 2. A transaction was made available, and the EJB resumed it,
>>>>>> but no
>>>>>> resources were actually enlisted, or perhaps resources were
>>>>>> enlisted
>>>>>> but not actually used, resulting in the same effect but relying
>>>>>> on
>>>>>> the TM to provide this information.
>>>>>>
>>>>>> I guess when you refer to a callback from Narayana, (2) is what
>>>>>> you're referring to? When would this information be available?
>>>>>> Maybe as some special result of suspending the transaction?
>>>>>>
>>>>>>
>>>>>> On 01/29/2016 12:27 PM, David M. Lloyd wrote:
>>>>>>
>>>>>> That's an interesting idea. So in effect, the remote EJB
>>>>>> would
>>>>>> tell the
>>>>>> caller "you sent me a transaction ID, but in the end, I
>>>>>> didn't
>>>>>> use it"?
>>>>>> I would need to think about how this might work in the
>>>>>> presence of
>>>>>> multiple concurrent invocations on the same transaction.
>>>>>>
>>>>>> Either way though, I think it would still be beneficial for
>>>>>> clients to
>>>>>> be able to explicitly annotate a client method (or otherwise
>>>>>> establish a
>>>>>> policy) such that it causes transactions to be propagated
>>>>>> (or
>>>>>> not), or
>>>>>> to enforce transaction-related preconditions. The
>>>>>> interceptor
>>>>>> that
>>>>>> implements this feature doesn't actually have protocol
>>>>>> awareness:
>>>>>> it
>>>>>> just examines the current environment, and decides whether
>>>>>> to
>>>>>> attach the
>>>>>> transaction to the invocation context.
>>>>>>
>>>>>> On 1/29/16 10:42 AM, Tom Jenkinson wrote:
>>>>>>
>>>>>> One option that I would favour is to go down the JTS
>>>>>> route
>>>>>> where the
>>>>>> subordinate calls back on the parent to tell it to
>>>>>> register
>>>>>> it in the
>>>>>> transaction. This could be a new JBoss Remoting API
>>>>>> that I
>>>>>> can invoke
>>>>>> from Narayana. The call would not necessarily be a
>>>>>> remote
>>>>>> call, it would
>>>>>> invoke back into the JBR transport to tell it that when
>>>>>> it
>>>>>> returns to
>>>>>> the parent it needs to enlist (or not).
>>>>>>
>>>>>> On 29 January 2016 at 15:47, David M. Lloyd
>>>>>> <david.lloyd at redhat.com <mailto:david.lloyd at redhat.com>
>>>>>> <mailto:david.lloyd at redhat.com
>>>>>>
>>>>>> <mailto:david.lloyd at redhat.com>>> wrote:
>>>>>>
>>>>>> As you may know, WildFly supports a feature
>>>>>> wherein an
>>>>>> EJB client
>>>>>> which
>>>>>> is invoking an EJB on a remote server has the
>>>>>> option
>>>>>> to
>>>>>> propagate its
>>>>>> local transaction to the remote server, treating
>>>>>> the
>>>>>> remote server
>>>>>> as a
>>>>>> subordinate and coordinating the transaction's
>>>>>> two-phase commit among
>>>>>> the resultant graph of servers. This feature has
>>>>>> always been
>>>>>> limited in
>>>>>> that, when enabled, transactions are always
>>>>>> propagated,
>>>>>> regardless of
>>>>>> the peer EJB's transaction policy, or of whether
>>>>>> the
>>>>>> peer even has a
>>>>>> transaction manager.
>>>>>>
>>>>>> So, for the invocation rework which I anticipate
>>>>>> will
>>>>>> be included in
>>>>>> WildFly 11, I've introduced a new client-side
>>>>>> annotation intended
>>>>>> to be
>>>>>> associated with the EJB interface which informs the
>>>>>> client library
>>>>>> what
>>>>>> to do for transaction propagation for that
>>>>>> interface.
>>>>>> In addition, I
>>>>>> intend to configuration strategies which will allow
>>>>>> the
>>>>>> default
>>>>>> mode to
>>>>>> be specified in various ways (per-thread, globally,
>>>>>> and
>>>>>> by target
>>>>>> interface/method all come to mind), for cases where
>>>>>> the
>>>>>> EJB's remote
>>>>>> interface cannot be easily modified for some
>>>>>> reason.
>>>>>> I
>>>>>> expect to
>>>>>> also
>>>>>> broaden these configuration strategies to apply to
>>>>>> all
>>>>>> client-side
>>>>>> EJB
>>>>>> interface/methods configuration items [3].
>>>>>>
>>>>>> The first part of this change is the addition of a
>>>>>> new
>>>>>> annotation
>>>>>> called
>>>>>> @ClientTransaction [1], which accepts as a value an
>>>>>> enum called
>>>>>> ClientTransactionPolicy [2]. The latter specifies
>>>>>> whether a local
>>>>>> transaction is required or forbidden for the
>>>>>> method or
>>>>>> interface, and
>>>>>> also specifies whether the transaction is
>>>>>> propagated
>>>>>> or
>>>>>> not
>>>>>> propagated.
>>>>>>
>>>>>> I've added copious amounts of JavaDoc in order to
>>>>>> establish
>>>>>> exactly what
>>>>>> the behavior of each mode is, as well as to specify
>>>>>> how
>>>>>> each mode
>>>>>> interacts with the various modules that are
>>>>>> configured
>>>>>> via the
>>>>>> standard
>>>>>> javax.ejb.TransactionAttributeType enum.
>>>>>>
>>>>>> [1]
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://github.com/jbossas/jboss-ejb-client/blob/master/src/main/java/org/jboss/ejb/client/annotation/ClientTransaction.java
>>>>>>
>>>>>> [2]
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://github.com/jbossas/jboss-ejb-client/blob/master/src/main/java/org/jboss/ejb/client/annotation/ClientTransactionPolicy.java
>>>>>>
>>>>>> [2] (raw)
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://raw.githubusercontent.com/jbossas/jboss-ejb-client/master/src/main/java/org/jboss/ejb/client/annotation/ClientTransactionPolicy.java
>>>>>>
>>>>>> [3] for a list, see:
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> https://github.com/jbossas/jboss-ejb-client/tree/master/src/main/java/org/jboss/ejb/client/annotation
>>>>>>
>>>>>>
>>>>>> --
>>>>>> - DML
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>>>>>> <mailto:wildfly-dev at lists.jboss.org>>
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>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> - DML
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>>
>>>>> - DML
>>>>>
>>>>>
>>>>>
>>>> --
>>> - DML
>>>
>>>
>>
> --
> - DML
>
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