API wise it could help you migrate once query side is out I guess. The type of the stream is simply Source[Any, _] (can be done with T), so if the rest of your app depends on such then you could do it.
Getting backpressure will require some gymnastics but should be doable (don't poll if no demand - done via not scheduling recover messages). -- Cheers, Konrad 'ktoso’ Malawski Akka @ Typesafe On 17 July 2015 at 12:43:03, Giovanni Alberto Caporaletti (paradi...@gmail.com) wrote: Hi Konrad do you think that creating a "streams adapter" that exposes the current PersistentView as a stream and then switching to the new impl when it's stable would be a good idea? On Friday, 17 July 2015 10:52:28 UTC+2, Konrad Malawski wrote: Hi guys, A few things to add to the discussion here :-) Multiple journals are supported in Akka Persistence since 2.4-M1. https://github.com/akka/akka/issues/15587 In general 2.4 will include all the things that were missing in persistence in its experimental phase. Push model: Akka PersistentViews queries the datasource every 4-5 sek by default. If you worry much about the time it takes for propagation and do not want to hammer the database for quick updates, you can implement a push version of above. Please note that this introduces an extra write for the channel. Actually this is the Pull model. The PersistentView is pulling from the datastore. The datastore is not pushing to the view. The new query side is actually pretty similar to streamz - it is a streams (akka streams) based abstraction on querying journals. Also, these can actually be "push", you could hook up a Source to a pubsub or eventstream (the akka ones, or different ones) for example. There will be a PR with it very soon, in general the direction is: (readJournal.query(...): Source[Any, _]) so you could .to(someOtherDatabaseSink) On Thu, Jul 16, 2015 at 10:28 AM, haghard <hagh...@gmail.com> wrote: -That looks like a convenient syntax that does the same thing as a persistent view does, tailored for users of scalaz streams, or am I missing something? Yes -Can you take multiple eventlogs and combine them into one reproducible ordered stream. So that if you make decisions (validate preconditions against that read model) based on that stream, can you guarantee that the next replay up would recreate the same results? I think that is where it becomes very tricky. The order you emit event is all up to you, scalaz-streams provide api for this purposes. You can build your read order based on some meta data in events or just read first available For example https://github.com/haghard/sport-center/blob/b35ccec59c65c674334ff7a1836bb54e829a1ed5/query-side-results/src/main/scala/view/ResultsViewRouter.scala#L43 среда, 15 июля 2015 г., 19:33:19 UTC+3 пользователь Magnus Andersson написал: Hi Hagard: That looks like a convenient syntax that does the same thing as a persistent view does, tailored for users of scalaz streams, or am I missing something? Can you take multiple eventlogs and combine them into one reproducible ordered stream. So that if you make decisions (validate preconditions against that read model) based on that stream, can you guarantee that the next replay up would recreate the same results? I think that is where it becomes very tricky. /Magnus Den tisdag 14 juli 2015 kl. 13:51:25 UTC+2 skrev haghard: Hi, Please take a look at https://github.com/krasserm/streamz You can read concrete journal with ```replay("processorA")``` and write in anywhere manually without interaction with PersistentView Hope it helps вторник, 14 июля 2015 г., 10:20:29 UTC+3 пользователь Amiri Barksdale написал: I've been reading up here on PersistentActor, and I think I get how that works to perform commands and write the result to an event store. I also think I understand that PersistentViews can subscribe to a PersistentActor and receive notification of each event stored for that PersistentActor type. I want to take a PersistentView and use it to update a separate Read datastore. I don't want to treat the PersistentView itself as a read store, but I want to make it trigger the creation or updating or saving of a "projection" of the event in some other store, like, e.g., Elasticsearch or Postgresql. Are there any guidelines, best practices, or examples of how to do this? One thread (https://groups.google.com/forum/#!searchin/akka-user/persistentview/akka-user/rMHjwBZpocQ/SmfAGMg7G68J) from June 2014 seemed to indicate that this sort of writing to another store would require PersistentViews to be able to read from multiple PersistentActors for this to be feasible. Is this still true? What is the path to take here, to get the actor system populating my read stores? Are people instead creating projections directly from the event store itself, like Greg Young's EventStore allows? Any insight is welcome! Amiri -- >>>>>>>>>> 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. -- Cheers, Konrad 'ktoso' Malawski Akka @ Typesafe -- >>>>>>>>>> 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. -- >>>>>>>>>> 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.
