Op vrijdag 16 mei 2014 09:43:33 UTC+2 schreef Patrik Nordwall: > > > > > On Fri, May 16, 2014 at 9:31 AM, Heiko Seeberger > <[email protected]<javascript:> > > wrote: > >> Couldn't we add a watchdog feature to Cluster Sharding itself? >> > > I don't think this is a core feature of Cluster Sharding and I think it > can be better implemented at the application level. For example, the > application knows how to send a message to a specific actor, since it is > the application that defines the id extractor. > > /Patrik >
I think it would be great from the developers perspective to be able to mark an actor to survive rebalancing (or crashes), so that the actor itself is re-created on the new node when the Shard is moved. Why do you think that this feature should *not* be part of the Cluster Sharding? What makes it application level? In my mind sharding is just configuration and not part of the application itself. It still leaves me wondering how I should prevent my whole cluster from going down when a node crashes and moving the shard results in an out-of-memory on the new node. To be clear, I don't have a real problem yet, but I'm trying to get my head around the cluster sharding concepts. Cheers, Jeroen > > > >> >> Heiko >> >> >> On Fri, May 16, 2014 at 9:25 AM, Patrik Nordwall >> <[email protected]<javascript:> >> > wrote: >> >>> Hi Jeroen, >>> >>> >>> On Thu, May 15, 2014 at 10:09 PM, Jeroen Gordijn >>> <[email protected]<javascript:> >>> > wrote: >>> >>>> Hi, >>>> >>>> When rebalancing a Shard, the old shard is stopped and a new shard is >>>> started on another node, after which all messages for that Shard will be >>>> send to the new node. When a message is received, the actor will be >>>> created. When Akka-persistence is used the Actor will reload all its >>>> events >>>> and restore state before processing the new message. But if no message is >>>> sent, the actor will not be created. This can be problematic when the >>>> actor >>>> is has some active state with retry mechanisme or timeout. Is my >>>> understanding correct? >>>> >>> >>> Your reasoning is correct. I think you can implement that by letting the >>> actor schedule a keep-alive message to itself, but via the ShardRegion. >>> Normally that will be local only message roundtrip via the scheduler and >>> local ShardRegion, but after rebalancing it will delegate the message to >>> the new node and thereby wake up the actor again. >>> >>> What this doesn't solve is when a node crashes. An actor living on that >>> node will not be automatically started somewhere else, until a message is >>> sent to it. To solve that I think you have to let the actor register itself >>> to a a few (for redundancy) watchdog actors, which watch the actor and know >>> how to send the wake-up message via ClusterSharding. >>> >>> Does that make sense? >>> >>> Cheers, >>> Patrik >>> >>> >>>> >>>> Is there a way to actively restore the Shard state when the shard is >>>> moved to another node? One problem I can see with this is when going back >>>> to less nodes. This means that the shards will be rebalanced, but >>>> potentially giving memory problems. This will cause rebalancing and memory >>>> problems on the next node and eventually putting the whole cluster down. >>>> Starting the cluster will be also problematic for the same reason. >>>> >>>> Cheers, >>>> Jeroen >>>> >>>> -- >>>> >>>>>>>>>> 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 [email protected] <javascript:>. >>>> To post to this group, send email to [email protected]<javascript:> >>>> . >>>> 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 [email protected] <javascript:>. >>> To post to this group, send email to [email protected]<javascript:> >>> . >>> Visit this group at http://groups.google.com/group/akka-user. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> >> >> -- >> >> Heiko Seeberger >> Twitter: @hseeberger >> Blog: blog.heikoseeberger.name >> >> -- >> >>>>>>>>>> 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 [email protected] <javascript:>. >> To post to this group, send email to [email protected]<javascript:> >> . >> 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
