Hi Michael, Any idea how that that is implemented? I understand this setting "cassandra-journal.pubsub-minimum-interval" is for Akka-Cassandra-Persistence but I wonder what exactly it leverages underneath from Cassandra or Cassandra driver?
Thanks, kant On Mon, Mar 13, 2017 at 1:57 AM, 'Michal Borowiecki' via Akka User List < akka-user@googlegroups.com> wrote: > Also, there's a setting called "cassandra-journal.pubsub-minimum-interval", > which if set will cause the journal to notify the persistence query side of > new writes, so it can only poll when needed instead of doing so > periodically. > Cheers, > Michal > > On 12/03/17 19:15, Patrik Nordwall wrote: > > Tal describes it very well. In the future we'll hopefully be able to get > notifications from Cassandra when something has changed instead of using > the primitive poll approach. There is already Change Data Capture (CDC) in > Cassandra but it's an extremely low level api so far. Improvement > suggestions based on CDC or something else very much welcome. > > /Patrik > sön 12 mars 2017 kl. 15:24 skrev Tal Pressman <kir...@gmail.com>: > >> Hi, >> >> I think the name for Persistence Query is a little misleading - when I >> first heard it I imagined something like an SQL query that can run over the >> data source, but that's not what it is. What it actually does is set up an >> Akka stream source that handles the events from the data store. The stream >> can be finite (like currentEventsByPersistenceId will stop once it has >> caught up with all the events) or infinite (like eventsByPersistenceId). In >> the second case, whenever there a new message is written to the data store >> (and the stream isn't back-pressured / busy) the source will emit the new >> message for the stream to handle. >> >> Now, as you've mentioned, there is no "push" mechanism for Cassandra, but >> that doesn't mean that everything breaks down. It simply means that when >> you use the CassandraReadJournal there is a thread that polls the DB and >> when there are new events there passes them down the stream. >> >> HTH, >> Tal >> >> >> On Sunday, March 12, 2017 at 4:09:02 PM UTC+2, kant kodali wrote: >> >> Hi All, >> >> I am trying to understand event sourcing in detail and I am new to Akka. >> One of book I was reading says a Persistence Actor will write events to a >> Journal so in my case the Journal is Cassandra and one can have Persistence >> Query Actor listen to the events from the Journal and this is where I don't >> understand how it works. More specifically, How does Persistence Query >> Actor know they are new events that it needs to Query for? I assume >> Persistence Actor and Persistence Query Actor are two separate things (so >> How does Persistence Query Actor gets notified that there are new events >> written by Persistence Actor) >> >> I would like to get live stream from Cassandra but I as far as I know I >> don't think there is any push based mechanism in Cassandra where Cassandra >> itself will push new events to some message bus or application. please >> correct me if I am wrong. >> >> Thanks, >> kant >> >> -- >> >>>>>>>>>> Read the docs: <http://akka.io/docs/>http://akka.io/docs/ >> >>>>>>>>>> Check the FAQ: >> <http://doc.akka.io/docs/akka/current/additional/faq.html> >> 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> >> akka-user@googlegroups.com. >> Visit this group at https://groups.google.com/group/akka-user. >> For more options, visit https://groups.google.com/d/optout. >> > -- > >>>>>>>>>> Read the docs: <http://akka.io/docs/>http://akka.io/docs/ > >>>>>>>>>> Check the FAQ: > <http://doc.akka.io/docs/akka/current/additional/faq.html> > http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> Search the archives: > <https://groups.google.com/group/akka-user>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 https://groups.google.com/group/akka-user. > For more options, visit https://groups.google.com/d/optout. > > > -- > <http://www.openbet.com/> Michal Borowiecki > Senior Software Engineer L4 > T: +44 208 742 1600 <+44%2020%208742%201600> > > > +44 203 249 8448 <+44%2020%203249%208448> > > > > E: michal.borowie...@openbet.com > W: www.openbet.com > OpenBet Ltd > > Chiswick Park Building 9 > > 566 Chiswick High Rd > > London > > W4 5XT > > UK > <https://www.openbet.com/email_promo> > This message is confidential and intended only for the addressee. 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