Hi Odd, that is a very good question: I was operating under the premise that EventsourcedProcessor is used quite a bit by now and renaming it might not be met with unlimited enthusiasm. The replacement for PersistentChannel will need to be named differently since the “persistent” in the name is confusing, but the details will have to wait until we have settled on its precise nature.
Perhaps we can do a “quick deprecation” for EventsourcedProcessor in 2.4-M1 (since it is marked “experimental” for this very reason), aliasing it until removal. I quite like PersistentActor, Processor is too generic. Opinions? Regards, Roland 20 maj 2014 kl. 22:39 skrev Odd Möller <odd.mol...@gmail.com>: > Hi! > > Just wanted to say that I love the idea of simplifying the abstractions as > suggested in this thread (all our processors are already of the event sourced > kind). One thing that occurred to me is if a similar simplification can be > done on the naming of the concepts: now that the names "Processor" and > "Channel" are unused, should the remaining concept still be called > "EventsourcedProcessor"? What about calling it "Processor", "PersistentActor" > or "EventsourcedActor" instead? Ditto regarding the reborn > "PersistentChannel". > > Greetings > Odd > > > On Tue, May 20, 2014 at 8:47 PM, 何品 <hepin1...@gmail.com> wrote: > I am using the persistent channel as a durable queue,and for it was not > recommend ,I switch to redis . > > 在 2014年5月21日星期三UTC+8上午2时32分38秒，rkuhn写道： > Hi Alex, > > I have filed the ticket for Processor’s removal > (https://github.com/akka/akka/issues/15230), which also talks about Channel > since that was only needed to contain the side-effecting replay nature of > command sourced processors. Your description below is rather terse, so it is > not fully clear to me how you are using Channel in this case and what a > replacement should be, can you elaborate? > > There is also the discussion ticket for reinventing PersistentChannel > (https://github.com/akka/akka/issues/15231) which might be of interest in > this context. My motivation here is to not remove needed functionality > without improved replacement. > > Regards, > > Roland > > 9 maj 2014 kl. 12:15 skrev ahjohannessen <ahjoha...@gmail.com>: > >> Hi Roland, >> >> We use Channel in conjunction with Eventsourced Processor (EP) in our >> applications in receiveRecover. >> It would be sad to see it go away without a reasonable alternative. >> >> One scenario in our apps is that we use DDD/ES and have a lot of EPs of same >> type, e.g. 10000 instances, >> that are loaded on demand by a supervisor. >> >> In order to have a single view on all of these, we inject an actor that >> wraps a single channel / aggregator EP combo >> into these instances on creation. This makes it possible to react to >> changes, even in case of JVM crashes, >> in that family of EPs as well as having a global view of that family. >> >> >> On Friday, May 9, 2014 9:13:17 AM UTC+1, rkuhn wrote: >> >> 9 maj 2014 kl. 09:58 skrev Martin Krasser <kras...@googlemail.com>: >> >>> >>> On 09.05.14 09:25, Roland Kuhn wrote: >>>> >>>> 9 maj 2014 kl. 09:08 skrev Martin Krasser <kras...@googlemail.com>: >>>> >>>>> >>>>> On 09.05.14 08:41, Roland Kuhn wrote: >>>>>> Hi Martin, >>>>>> >>>>>> 9 maj 2014 kl. 08:05 skrev Martin Krasser <kras...@googlemail.com>: >>>>>> >>>>>>> Hi Roland, >>>>>>> >>>>>>> thanks for starting a discussion on this. Here are some initial >>>>>>> thoughts on your proposal: >>>>>>> >>>>>>> "... very same throughput optimization by applying the state changes >>>>>>> before persisting them ..." >>>>>>> >>>>>>> I think we agree that whatever changes are going to be made in the >>>>>>> future, we must keep the throughput optimizations (by batching >>>>>>> writes/updates). As you said, with an EP, this can only be achieved by >>>>>>> applying events to current state *before* persisting them. Furthermore, >>>>>>> to enable batching, an EP must therefore be able to process new >>>>>>> commands while (previous) events are about to be persisted. This >>>>>>> however has a very important consequence for commands that read current >>>>>>> state. If we allow events to be applied to current state *before* >>>>>>> persisting them, we allow clients to read state from that EP that may >>>>>>> not be re-readable after a crash. For example: >>>>>>> >>>>>>> - EP receives update command, derives event and applies it immediately >>>>>>> to current state >>>>>>> - EP (asynchronously) persists event >>>>>>> - EP receives a read command (while event persistence is in progress) >>>>>>> - EP (successfully) returns read response to requestor >>>>>>> - EP JVM crashes before event was successfully persisted >>>>>>> - EP state cannot be reconstructed i.e. previous read cannot be >>>>>>> repeated. >>>>>> >>>>>> This is only true if the recovery is incomplete: the update command will >>>>>> not have been acknowledged at this point, so if someone cared about it >>>>>> they will send it again during recovery and the EP will eventually end >>>>>> up in a state where the read will return the same value again. If this >>>>>> type of consistency is not good enough, then you can always defer reads >>>>>> within the write model until after persistence is completed, meaning >>>>>> that the read is only performed once a corresponding read “event” has >>>>>> gone through the journal. We could allow events that are only looped >>>>>> through to make this work, just like non-Persistent commands are looped >>>>>> today (and for the same reason). >>>>> >>>>> Delaying reads is only an option when reads are made via messages to a >>>>> (E)P. If my processor manages state via an STM ref where only the >>>>> processor updates the STM ref but reads go directly to the STM ref, then >>>>> you cannot delay reads. >>>> >>>> In this scenario you would delay updating the STM ref until after the >>>> persistence loop, which is exactly the same as for a current >>>> command-sourced Processor: the read gets delayed until after the writes >>>> are processed, in the same way the STM ref update gets delayed by the >>>> write having to go through the journal. Effects, consistency and latency >>>> are the same in both implementations. >>> >>> That's true. So, to achieve >>> >>> - repeatable reads >>> - low read latency and >>> - high write throughput >>> >>> reads can go to the STM refs directly and EP must update the STM ref only >>> after having persisted the events. If one *additionally* wants to achieve >>> >>> - read-your-own-write consistency (assuming a client issues an update >>> command, immediately followed by a read command) >>> >>> one would need a way to loop read commands through the journal as well >>> before serving them (which probably requires an addition to the API then). >>> Alternatively, a client only issues a read after having received a >>> write-ack (at the cost of an additional roundtrip). >> >> This is an interesting remark: normally read-your-writes is only guaranteed >> for reads submitted after having received the ACK for the write, so what we >> are providing here is actually a qualitative improvement on that status quo >> that is only possible in Reactive systems (normally the ACK is signaled by a >> synchronous non-exceptional method return). >> >>> Anyway, I think you convinced me, as usual :) Great proposal, Dr Kuhn! >> >> And as usual you helped in refining the proposal: the addition of looping >> non-persistent events through the journal is an important one, thanks for >> providing the use-case! >> >> So, to summarize, we can incorporate all current functionality provided by >> Processor and Channel into EventsourcedProcessor by adding the following two >> features: >> >> the ability to opt out of stashing everything while waiting for persist()ing >> the ability to loop non-persistent events through the journal >> >> Everyone, please consider what this would mean for your code base and >> comment, now is the right time to speak up! The same goes for opinions on >> whether PersistentChannel pulls its weight or not (as argued earlier in this >> thread). >> >> Regards, >> >> Roland >> >>> >>> Cheers, >>> Martin >>> >>> -- >>> >>>>>>>>>> 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. >> >> >> >> Dr. Roland Kuhn >> Akka Tech Lead >> Typesafe – Reactive apps on the JVM. >> twitter: @rolandkuhn >> >> >> >> -- >> >>>>>>>>>> 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. > > > > > Dr. Roland Kuhn > Akka Tech Lead > Typesafe – Reactive apps on the JVM. > twitter: @rolandkuhn > > > > -- > >>>>>>>>>> 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. Dr. Roland Kuhn Akka Tech Lead Typesafe – Reactive apps on the JVM. twitter: @rolandkuhn -- >>>>>>>>>> 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.
