[wildfly-dev] EJB Transactions Graceful Shutdown

[Gytis Trikleris]

Flavia,

it seems that it might be better for EJB subsystem to keep track of its 
own transaction. The reason being that all transactions are kept in the 
same map no matter what created them (EJB, CDI, or UserTransaction).

We could expose an API to get that map (or just a number of transactions 
in it) as well as a way to register callback. However, that will also 
include transactions created by other ways mentioned above.

Gytis


On 05/12/2016 20:34, Flavia Rainone wrote:
> I think we can keep open transaction tracking only inside transactions 
> subsystem while we are not shutting down, and then we can enroll for 
> notification of open active transactions only on suspend if needed... 
> IMHO that's as clean as we can get regarding shutdown code when the 
> server is in running state.
>
> I would go with some sort of ActiveTransactionListener, that would be 
> notified of no more active transactions only if the listener is set?
>
> Something along the lines below at ejb side:
>
> ServerActivityCallback callback = null;
>
> public void suspend(ServerActivityCallback callback) {
>     if ( transactionSubsystem.getActiveTransactions() > 0) {
>        transactionSubsystem.setActiveTransactionsListener(this);
>     }
>     else {
>       callback.done(); // done suspending
>    }
> }
>
> // listener method
> public void noMoreActiveTransactions() {
>     callback.done(); // done suspending
>     // then we let control point notify clients that this node is no 
> longer available
>     ...
> }
>
> At transactions side:
> ActiveTransactionListener listener = null;
>
> private void incrementTxnCount() {
>     ...
> }
>
> private void decrementTxnCount() {
>    if (txnCountUpdater.decrementAndGet() == 0 && listener != null)
>        listener.noMoreActiveTransactions();
> }
>
> public int getActiveTransactions() {
>    return txnCountUpdater.get();
> }
>
>
>
>
>
>
>
> On 04-12-2016 20:39, Stuart Douglas wrote:
>> On Sat, Dec 3, 2016 at 3:40 AM, Flavia Rainone<frainone at redhat.com>  wrote:
>>> Hi,
>>>
>>> I'm creating this thread to discuss the remaining details of graceful
>>> shutdown for ejb transactions.
>>>
>>> This is more or less what I've done so far:
>>>
>>> https://github.com/fl4via/wildfly/commit/7017146522af9a979a8a8e0c92039e6a5fb18760
>>>
>>> While discussing this in the hip chat yesterday, Stuart mentioned that maybe
>>> we could have the transactions subsystem responsible for keeping track of
>>> how many active transactions we have, instead of putting that code in
>>> EjbRemoteTransactionsRepository.
>>>
>>> Stuart, does that include having the suspend callback being done at
>>> transactions subsystem as well? I'm thinking maybe not, because there are
>>> two points in the ejb subsystem we need to know if transactions suspension
>>> is over:
>>>
>> No, that still has to be handled at an EJB subsystem level.
>> Conceptually this is similar to what was done for the XTS subsytem, so
>> it should probably use a similar design. Ideally while the server is
>> in the running state the only graceful related code that is run is the
>> control point request tracking, however this may not be possible.
>>
>> One other thing that came up on our hipchat discussion yesterday is TX
>> level graceful shutdown actually has some significant drawbacks, as
>> you cannot send out the module unavailability message until all the
>> transactions have been closed. This means that while we are waiting
>> for transactions to complete the node will still be part of a cluster,
>> and clients will send it requests that will be immediately rejected.
>>
>> Stuart
>>
>>> - at EjbSuspendInterceptor if it is over, no request is allowed, if it is
>>> not over, we need to check if current invocation contains a reference to an
>>> active transaction
>>>
>>> - at some point, we need to let control point notify that the ejb module is
>>> not longer available to ejb client after transaction suspension is over,
>>> i.e., we need to do that when suspend has been requested and there are no
>>> remaining active transactions available.
>>>
>>> On the other hand, it is hard to draw the line between what should be in the
>>> transactions subsystem and what shouldn't. If the callback is done at
>>> transactions subsystem, we need a way of having ejb3 notified that it is
>>> done. If it is not done at transactions subsystem, ejb3 has to be notified
>>> of the active transactions going to zero, which seems a lot of overhead, so
>>> from this point of view maybe the callback should be in the transactions
>>> system after all.
>>>
>>> Stuart and Gytis, any thoughts?
>>>
>>>
>>> --
>>> Flavia Rainone
>>> Principal Software Engineer
>>> JBoss EAP/WildFly Team
>>> M: (+55) 11 981-225-466
>>>
>>> Red Hat.
>>> Better technology.
>>> Faster innovation.
>>> Powered by community collaboration.
>
> -- 
> Flavia Rainone
> Principal Software Engineer
> JBoss EAP/WildFly Team
> M: (+55) 11 981-225-466
>
> Red Hat.
> Better technology.
> Faster innovation.
> Powered by community collaboration.

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