On Thu, Jan 22, 2015 at 9:01 PM, Yann Simon <yann.simon...@gmail.com> wrote:
> Hi Patrick, > > Le dimanche 20 avril 2014 16:59:22 UTC+2, Patrik Nordwall a écrit : >> >> >> >> >> On Sun, Apr 20, 2014 at 2:47 PM, Olger Warnier <ol...@spectare.nl> wrote: >> >>> Hi Patrick, >>> >>> Sounds like an interesting approach, storing some meta-data at the view >>> may help to check / show the reliability of the system. >>> >>> At this moment the events are sent to a processor per node that >>> publishes the event (distributed pub sub) >>> >> >> That sounds good, as well. >> >> >>> When you talk about view, that's the akka-persistence view ? >>> >> >> Yes, persistence.View and persistence.Processor >> >> >>> So more or less, the sub processors could send messages to the View and >>> when there is a Persist() around it, it will be stored. >>> >> >> I'm not sure I understand what you mean here. Let me clarify my proposal >> with an example. Let's say we have a User aggregate root with some profile >> information that can be updated. The user is represented by a User >> EventsourcedProcessor actor, which is sharded. On the query side we want to >> be able to search users by first and last name, i.e. we want to store all >> users in a relational database table on the query side. >> >> The User actor persist FirstNameChanged, and inside the persist block it >> sends a Persistent(FirstNameChanged) message to the AllUsers Processor. On >> the query side we have a AllUsersView connected to that processor. When >> AllUsersView receives FirstNameChanged it updates the db table. >> >> To handle lost messages between User and AllUsers you might want to send >> an acknowledgement from AllUsers to User, and have a retry mechanism in >> User. I would implement that myself in User, but PersistentChannel might be >> an alternative. >> > > Let's say the current version in production only have User actors. > Now we want to deliver an new version that include the new Query with the > AllUsers Processor. > How can we be sure that AllUsers receive all the events to be able to > construct its state? > I'm afraid there is no API to retrieve all ids, see feature request https://github.com/akka/akka/issues/13892 For the moment I guess you have to try to retrieve them from the journal data store. Regards, Patrik > > Thanks in advance, > Yann > >> >> >> >> >>> >>> Is that a correct understanding ? >>> >>> Kind regards, >>> >>> Olger >>> >>> >>> On Sunday, April 20, 2014 2:32:07 PM UTC+2, Patrik Nordwall wrote: >>> >>>> Hi Olger, >>>> >>>> What if you keep the sharded event sourced actors (+10k), but let them >>>> also send the events to one or a few processors. Then you can connect the >>>> views/streams to these processors. >>>> >>>> If you don't like storing the events twice you can instead store some >>>> meta-data (processor-id, seq-no,timestamp) and have a view that creates >>>> sub-views on demand from the replayed meta-data. The sub-views would >>>> forward to the parent aggregated view. >>>> >>>> /Patrik >>>> >>>> 19 apr 2014 kl. 20:46 skrev Olger Warnier <ol...@spectare.nl>: >>>> >>>> >>>> Hi Martin, >>>> >>>> Had to think about it a little, hereby my follow up. (hope you don't >>>> mind the continues discussion, it helps me a lot in defining the right >>>> approach, thanks for that) >>>> >>>> On Saturday, April 19, 2014 7:11:23 AM UTC+2, Martin Krasser wrote: >>>>> >>>>> Hi Olger, >>>>> >>>>> installing 10k views/producers won't scale, at least not with the >>>>> current implementation. Here are some alternatives: >>>>> >>>> Intresting, what would need to change to have is scaling ? >>>> (Idea is to have the eventsourcedprocessors reflect a DDD style >>>> Aggregate Root instance and have those distributed using cluster sharding) >>>> >>>> >>>>> >>>>> - Maybe a custom journal plugin is what you need: a plugin that >>>>> delegates all write/read requests to the actual journal actor and that >>>>> additionally updates a database with the events to be written. This >>>>> essentially installs a single "listener" per ActorSystem (this is to some >>>>> extend comparable to a database trigger that executes additonal commands. >>>>> If the backend datastore supports that directly, I recommend implementing >>>>> the trigger there, if possible). >>>>> >>>> >>>> I am not sure, if I understand it.. the basic idea is to have the >>>> 'events' stored via the eventsourcedprocessor being published to 'n' views. >>>> The actual number of view that need to listen to these events are not known >>>> up front (people can add their own views... at system startup, it will be >>>> clear) >>>> As every eventsourced actor is actually an AggregateRoot (in DDD terms) >>>> and thereby something of an instance with it's own state, the changes in >>>> these states need to be aggregated (that can be done with the streaming as >>>> you mention) and published to the views that are interested (subscribed). >>>> Doing this by hand in the aggregate root actor is not a problem, >>>> thereafter write your own listener actor and that will populate a view data >>>> store. Still I have the feeling that the actual 'View' (or ViewProducer) >>>> could be implemented in such a way that it's done by the view. >>>> >>>> >>>>> >>>>> - Instead of having thousands of processors, what speaks against >>>>> combining them into a single processor (or only a few) per node? >>>>> >>>> This would mean that I'll have all my aggregate root instances running >>>> in 1 processor meaning that I need to reconstruct state per aggregate root >>>> instance in some way. Using EventsourcedProcessor, I'd expect that I need >>>> to replay everything for all instances and pick the one that I need for >>>> processing at that moment. (this can of course be optimized with snapshots >>>> and something like memcached). This appears to be a performance hit as I >>>> feel it. >>>> >>>> >>>>> >>>>> Further comments inline ... >>>>> >>>>> On 18.04.14 16:10, Olger Warnier wrote: >>>>> >>>>> Hi Martin, >>>>> >>>>> >>>>> I'm currently working on view composition using the brand new >>>>>> akka-stream module. Basic idea is to make views stream producers and to >>>>>> use >>>>>> the akka-stream DSL to merge message/event streams from several producers >>>>>> into whatever you need. See also https://twitter.com/mrt1nz/sta >>>>>> tus/457120534111981569 for a first running example. >>>>>> >>>>>> WDYT? >>>>>> >>>>> >>>>> First of all Nice stuff !, I think this is useful for the system at >>>>> my hands (real-time patient monitoring based on medical data) >>>>> I've seen the streams announcements but did not dive into that yet. >>>>> Looking at your code StreamExample.scala it more or less 'clicks' in >>>>> concept. (and hopefully in the right way) >>>>> >>>>> From a 'View' perspective as currently is available in >>>>> akka-persistence, every producing actor needs a view attached to it in >>>>> order to push the events to the streams producer, right ? (when I look at >>>>> the ViewProducer.scala code, this is what is done.) >>>>> >>>>> PersistentFlow.fromProcessor("p1").toProducer(materializer) >>>>> Now, I have a sharding cluster with an EventsourcedProcessor (expect >>>>> 10.000ths of these EventsourcedProcessor actor instances) , so I'll need >>>>> to >>>>> create a line like this for every EventsourcedProcessor in order to get >>>>> the >>>>> stream of events together. Thereafter, I need to merge them together to >>>>> get >>>>> a single stream of events. (at least that is one of the features of using >>>>> the streams) >>>>> >>>>> >>>>> Every processor instance itself could create such a producer during >>>>> start and send it to another actor that merges received producers. >>>>> >>>> That would not allow me to implement 'View' (as is known in the >>>> persistence package) in order to listen to events within my cluster of >>>> aggregate root instances, I'll need to build something additional for that >>>> (as View is more used for the collection of those events and thereafter >>>> will push them through) >>>> >>>> At this moment, I use an akka extension (gives more or less a >>>> singleton) that is used directly in the EventSourcedProcessor after storage >>>> (persist) of the event. >>>> Thereafter I have listeners that get these events and transform them >>>> into data that needs storage for a certain type of view (CQRS style) (this >>>> is where I expected the 'View' to be used) >>>> >>>>> >>>>> >>>>> My goal is to have 'Listeners' (that is my interpretation of a >>>>> 'View' due to historic reasons...) that will for instance update a data >>>>> store, this will probably happen on on just a few nodes (maybe 1 and some >>>>> failover stuff). These 'Listeners' need to attach to the sharded >>>>> Eventsourced system and ask to get all event sourced events forwarded. >>>>> (publish subscribe more or less). >>>>> >>>>> I wonder if the current View (or ViewProducer) fits this situation >>>>> due to the fact you need to create as many views as eventsourcedprocessors >>>>> are created. >>>>> With the merged streams thereafter, it seems a possibility to have >>>>> just one thing per node (I assume actor) that will do the writing to a >>>>> data >>>>> store (not being the eventstore). >>>>> What would be the way to get these Views 'automagically' attached to >>>>> the proper procesors ? >>>>> >>>>> >>>>> See above. >>>>> >>>>> >>>>> And, do you have a pointer how this issue is solved with it's own >>>>> eventstore ? In a sharding cluster, you more or less have the same issue. >>>>> (would streams change your approach there ?) >>>>> >>>>> >>>>> There's one journal actor per ActorSystem where n journal actors in a >>>>> cluster update a replicated journal >>>>> <http://akka.io/community/#plugins_to_akka_persistence>. >>>>> >>>> Thanks, thats not done as an akka extension right ? (why not ?) >>>> >>>>> >>>>> Hope that helps. >>>>> >>>> Certainly, really appreciate your patience. >>>> >>>>> >>>>> Cheers, >>>>> Martin >>>>> >>>> >>>> Kind regards, >>>> >>>> Olger >>>> >>>> >>>> -- >>>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>> >>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/c >>>> urrent/additional/faq.html >>>> >>>>>>>>>> Search the archives: https://groups.google.com/grou >>>> p/akka-user >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "Akka User List" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to akka-user+...@googlegroups.com. >>>> To post to this group, send email to akka...@googlegroups.com. >>>> >>>> Visit this group at http://groups.google.com/group/akka-user. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>>> -- >>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>> >>>>>>>>>> Check the FAQ: http://doc.akka.io/docs/akka/ >>> current/additional/faq.html >>> >>>>>>>>>> Search the archives: https://groups.google.com/ >>> group/akka-user >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Akka User List" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to akka-user+...@googlegroups.com. >>> To post to this group, send email to akka...@googlegroups.com. >>> Visit this group at http://groups.google.com/group/akka-user. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> >> Patrik Nordwall >> Typesafe <http://typesafe.com/> - Reactive apps on the JVM >> Twitter: @patriknw >> JOIN US. REGISTER TODAY! <http://www.scaladays.org/> >> Scala <http://www.scaladays.org/> >> Days <http://www.scaladays.org/> >> June 16th-18th, <http://www.scaladays.org/> >> Berlin <http://www.scaladays.org/> >> >> -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to akka-user+unsubscr...@googlegroups.com. > To post to this group, send email to akka-user@googlegroups.com. > Visit this group at http://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > -- Patrik Nordwall Typesafe <http://typesafe.com/> - Reactive apps on the JVM Twitter: @patriknw -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. 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