[infinispan-dev] Remote Hot Rod events wiki updated

Wed Apr 16 11:38:07 EDT 2014

On Wed, Apr 16, 2014 at 11:14 AM, Galder Zamarreño <galder at redhat.com> wrote:
>
> On 11 Apr 2014, at 15:25, Radim Vansa <rvansa at redhat.com> wrote:
>
>> OK, now I get the picture. Every time we register to a node (whether the
>> first time or after previous node crash), we receive all (filtered) keys
>> from the whole cache, along with versions. Optionally values as well.
>
> Exactly.
>
>> In case that multiple modifications happen in the time window before
>> registering to the new cache, we don't get the notification for them,
>> just again the whole cache and it's up to application to decide whether
>> there was no modification or some modifications.
>
> I’m yet to decide on the type of event exactly here, whether cache entry created, cache entry modified or a different one, but regardless, you’d get the key and the server side version associated with that key. A user provided client listener implementation could detect which keys’ versions have changed and react to that, i.e. lazily fetch new values. One such user provided client listener implementation could be a listener that maintains a near cache for example.

My current code was planning on raising a CacheEntryCreatedEvent in
this case.  I didn't see any special reason to require a new event
type, unless anyone can think of a use case?

>
>> As the version for
>> entries is incremented per cache and not per value, there is no way to
>> find out how many times the entry was modified (we can just know it was
>> modified when we remember the previous version and these versions differ).
>
> Exaclty, the only assumption you can make is that the version it’s different, and that’s it’s a newer version that the older one.
>
>> Thanks for the clarifications, Galder - I was not completely sure about
>> this from the design doc.
>
> No probs
>
>> Btw., could you address Dan's question:
>>
>> "Don't we want to allow the user to pass some data to the filter factory
>> on registration?
>> Otherwise we'd force the user to write a separate filter factory class
>> every time they want to track changes to a single key."
>>
>> I know this was already asked several times, but the discussion has
>> always dissolved. I haven't seen the final "NO”.
>
>>
>> Radim
>>
>> On 04/11/2014 02:36 PM, Galder Zamarreño wrote:
>>> On 04 Apr 2014, at 19:11, William Burns <mudokonman at gmail.com> wrote:
>>>
>>>> On Fri, Apr 4, 2014 at 3:29 AM, Radim Vansa <rvansa at redhat.com> wrote:
>>>>> Hi,
>>>>>
>>>>> I still don't think that the document covers properly the description of
>>>>> failover.
>>>>>
>>>>> My understanding is that client registers clustered listeners on one server
>>>>> (the first one it connects, I guess). There's some space for optimization,
>>>>> as the notification will be sent from primary owner to this node and only
>>>>> then over hotrod to the client, but I don't want to discuss it now.
>>>> There could be optimizations, but we have to worry about reordering if
>>>> the primary owner doesn't do the forwarding.  You could have the case
>>>> of multiple writes to the same key from the clients and lets say they
>>>> send the message to the listener after they are written to the cache,
>>>> there is no way to make sure they are done in the order they were
>>>> written to the cache.  We could do something with versions for this
>>>> though.
>>> Versions do not provide global ordering. They are used, at each node, to identify an update, so they’re incrementing at the node level, mixed with some other data that’s node specific to make them unique cluster wide. However, you can’t assume global ordering based on those with the current implementation. I agree there’s room for optimizations but I think correctness and ordering are more important right now.
>>>
>>>>>> Listener registrations will survive node failures thanks to the underlying
>>>>>> clustered listener implementation.
>>>>> I am not that much into clustered listeners yet, but I think that the
>>>>> mechanism makes sure that when the primary owner changes, the new owner will
>>>>> then send the events. But when the node which registered the clustered
>>>>> listener dies, others will just forgot about it.
>>>> That is how it is, I assume Galder was referring to node failures not
>>>> on the one that registered the listener, which is obviously talked
>>>> about in the next point.
>>> That’s correct.
>>>
>>>>>> When a client detects that the server which was serving the events is
>>>>>> gone, it needs to resend it's registration to one of the nodes in the
>>>>>> cluster. Whoever receives that request will again loop through its contents
>>>>>> and send an event for each entry to the client.
>>>>> Will that be all entries in the whole cache, or just from some node? I guess
>>>>> that the first is correct. So, as soon as one node dies, all clients will be
>>>>> bombarded by the full cache content (ok, filtered). Even if these entries
>>>>> have not changed, because the cluster can't know.
>>>> The former being that the entire filtered/converted contents will be sent over.
>>> Indeed the former, but the entire entry, only keys, and latest versions, will be sent by default. Converters can be used to send value side too.
>>>
>>>>>> This way the client avoids loosing events. Once all entries have been
>>>>>> iterated over, on-going events will be sent to the client.
>>>>>> This way of handling failure means that clients will receive at-least-once
>>>>>> delivery of cache updates. It might receive multiple events for the cache
>>>>>> update as a result of topology changes handling.
>>>>> So, if there are several modifications before the client reconnects and the
>>>>> new target registers the listener, the clients will get only notification
>>>>> about the last modification, or rather just the entry content, right?
>>> @Radim, you don’t get the content by default. You only get the key and the last version number. If the client wants, it can retrieve the value too, or using a custom converter, it can send back the value, but this is optional.
>>>
>>>> This is all handled by the embedded cluster listeners though.  But the
>>>> end goal is you will only receive 1 event if the modification comes
>>>> before value was retrieved from the remote node or 2 if afterwards.
>>>> Also these modifications are queued  by key and so if you had multiple
>>>> modifications before it retrieved the value it would only give you the
>>>> last one.
>>>>
>>>>> Radim
>>>>>
>>>>>
>>>>> On 04/02/2014 01:14 PM, Galder Zamarreño wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> I've finally managed to get around to updating the remote hot rod event
>>>>> design wiki [1].
>>>>>
>>>>> The biggest changes are related to piggybacking on the cluster listeners
>>>>> functionality in order to for registration/deregistration of listeners and
>>>>> handling failure scenarios. This should simplify the actual implementation
>>>>> on the Hot Rod side.
>>>>>
>>>>> Based on feedback, I've also changed some of the class names so that it's
>>>>> clearer what's client side and what's server side.
>>>>>
>>>>> A very important change is the fact that source id information has gone.
>>>>> This is primarily because near-cache like implementations cannot make
>>>>> assumptions on what to store in the near caches when the client invokes
>>>>> operations. Such implementations need to act purely on the events received.
>>>>>
>>>>> Finally, a filter/converter plugging mechanism will be done via factory
>>>>> implementations, which provide more flexibility on the way filter/converter
>>>>> instances are created. This opens the possibility for filter/converter
>>>>> factory parameters to be added to the protocol and passed, after
>>>>> unmarshalling, to the factory callbacks (this is not included right now).
>>>>>
>>>>> I hope to get started on this in the next few days, so feedback at this
>>>>> point is crucial to get a solid first release.
>>>>>
>>>>> Cheers,
>>>>>
>>>>> [1] https://github.com/infinispan/infinispan/wiki/Remote-Hot-Rod-Events
>>>>> --
>>>>> Galder Zamarreño
>>>>> galder at redhat.com
>>>>> twitter.com/galderz
>>>>>
>>>>> Project Lead, Escalante
>>>>> http://escalante.io
>>>>>
>>>>> Engineer, Infinispan
>>>>> http://infinispan.org
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> infinispan-dev mailing list
>>>>> infinispan-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Radim Vansa <rvansa at redhat.com>
>>>>> JBoss DataGrid QA
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> infinispan-dev mailing list
>>>>> infinispan-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
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>>>
>>> --
>>> Galder Zamarreño
>>> galder at redhat.com
>>> twitter.com/galderz
>>>
>>>
>>> _______________________________________________
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>>> infinispan-dev at lists.jboss.org
>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>
>>
>> --
>> Radim Vansa <rvansa at redhat.com>
>> JBoss DataGrid QA
>>
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>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>
>
> --
> Galder Zamarreño
> galder at redhat.com
> twitter.com/galderz
>
>
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