[hibernate-dev] Hibernate Search 421 [Exceptions happening in backend are unnoticed]

[Emmanuel Bernard]

Hello Amin,
Have you had a chance to work on this?

Emmanuel

On 9 janv. 2010, at 15:59, Amin Mohammed-Coleman wrote:

> Hi Sanne
> 
> Thanks for the advice! I'll take a look at it.
> 
> 
> Cheers
> Amin
> 
> On Sat, Jan 9, 2010 at 1:34 PM, Sanne Grinovero
> <sanne.grinovero at gmail.com>wrote:
> 
>> Hi Amin,
>> I've been looking a bit in this, but didn't take any action as we
>> didn't discuss any strategy, so glad you join in propose something.
>> I didn't think of jms, it's ok we provide some way for the end user to
>> override whatever we provide, but I think we should just provide
>> the basic stuff: logging the error or propagate it back when possible.
>> And then add some extensibility like plugin loading the usual way.
>> 
>> Originally (Hibernate Search 3.0.x) the changes made to different
>> indexes were serialized, so when using the "sync" backend the same
>> process would have applied changes to the index and, in case of
>> exceptions, this would have been propagated up to user's code making
>> it impossible to go unnoticed, or at least moving responsibility of
>> handling it to the developer.
>> When using the "async" mode for backend a different thread would have
>> handled the indexwriter, so in case of an exception the error would
>> have killed the separate thread, go unnoticed, and as we use a
>> ThreadPool a new thread would have been spawned to replace the failed
>> one.
>> 
>> Since Search 3.1.x both "sync" and "async" use a separate thread - to
>> be able to apply changes to different indexes in parallel - so
>> exceptions are going unnoticed by user code even in "sync" mode. Look
>> into "run" method of
>> org.hibernate.search.backend.impl.lucene.LuceneBackendQueueProcessor,
>> it creates a org.hibernate.search.backend.impl.lucene.QueueProcessors
>> where most of this logic resides.
>> This impl will use either runAllAsync() or runAllWaiting() depending
>> on backend configuration (async/sync). The Async version just
>> schedules the different tasks, the sync one is going to do the same
>> but will wait for all of them to have finished before returning
>> control, making sure to implement the sync behaviour even while using
>> several threads to perform it. I was inspired by
>> 
>> java.util.concurrent.AbstractExecutorService.invokeAll(Collection<Callable<T>>
>> tasks), as mentioned in code comments, which is ignoring
>> ExecutionException, so this empty catch block should be used now to do
>> something.
>> 
>> I'd suggest to provide this defaults:
>> 
>> * for sync backend:
>>  by default: rethrow the exception (like old behaviour)
>>  configurable alternative: log it
>> 
>> * for async backend:
>>  log it (it's not useful to rethrow as nobody is listening on it)
>> 
>> To handle these cases only you would add the log statement, an rethrow
>> it, fixing the QueueProcessors code.
>> To give full control to the end user of what to do, I'd suggest to let
>> him specify an implementationf of
>> java.lang.Thread.UncaughtExceptionHandler
>> and so we can set that on the thread.
>> The backend is using the default JVM "Executors.newFixedThreadPool( 1
>> );"  (initialized at
>> org.hibernate.search.backend.impl.lucene.PerDPResources:51)
>> but we could change that to use the Search Executor factory
>> "org.hibernate.search.batchindexing.Executors" I later added for the
>> batchbackend.
>> The nice thingy for this Executor is that it customizes the thread
>> names so you can easily spot Search's threads in monitoring/debugging
>> tools;
>> we could have a setUncaughtExceptionHandler( userImplementation ) in
>> org.hibernate.search.batchindexing.Executors:85.
>> If you change it there, the same handler would be used to manage
>> errors in the batch indexer, so you solve both problems at once.
>> Our "log the error" implementation would be the nice default for an
>> exception handler, but still I'd like to make sure the user code will
>> get the error propagated when
>> using async mode.
>> 
>> Cheers,
>> Sanne
>> 
>> 
>> 2010/1/9 Amin Mohammed-Coleman <aminmc at gmail.com>:
>>> Hi All
>>> 
>>> Emmanuel asked me to look at this issue (HSearch 421) where exceptions
>>> happening in backend process which are going unnoticed.  I was wondering
>> if
>>> I could get some advice/thoughts on how to tackle the problem.    The
>> issue
>>> mentioned providing the user the option to decide how to handle
>> exceptions
>>> (for example queues, logs, etc), so I'm guessing there needs to be some
>>> custom option that the user will need to set up, maybe something like
>> this?
>>> 
>>> exception_handling_strategy=jms
>>> exception_handling_strategy_jms_queue=
>>> 
>>> or if they wanted to log the exceptions:
>>> 
>>> exception_handling_strategy=log
>>> 
>>> or the user could create a custom class which implements a particular
>>> interface to handle exceptions
>>> 
>>> exception_handling_strategy=custom
>>> exception_handling_custom_class=ExceptionHandling
>>> 
>>> I could be completely wrong in the above approach and therefore would be
>>> grateful for any input.
>>> 
>>> 
>>> Cheers
>>> Amin
>>> _______________________________________________
>>> hibernate-dev mailing list
>>> hibernate-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>> 
>> 
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