Andrey, I think your approach works, but it requires periodical polling from queue. Continuous queries provide an ability to get push notifications for updates, which from my experience is critical for some use cases.
-Val On Mon, Jul 27, 2015 at 7:35 AM, Andrey Kornev <andrewkor...@hotmail.com> wrote: > I wonder if the same result (guaranteed delivery of CQ notifications) can > be achieved entirely in the "user space" using the public Ignite API only? > > For example: > - start a server-side CQ and have the listener push the notifications into > an IgniteQueue. > - have the client connect to the queue and start receiving the > notifications. > > Regards > Andrey > > > From: dsetrak...@apache.org > > Date: Sun, 26 Jul 2015 22:15:09 -0700 > > Subject: Re: Continuous queries changes > > To: dev@ignite.incubator.apache.org > > > > On Sat, Jul 25, 2015 at 8:07 AM, Andrey Kornev <andrewkor...@hotmail.com > > > > wrote: > > > > > Val, > > > > > > I'm sorry for being obtuse. :) > > > > > > I was simply wondering if the queue is going to be holding all > unfiltered > > > events per partition or will there be a queue per continuous query > instance > > > per partition? Or, is it going to be arranged some other way? > > > > > > > I believe that backup queues will have the same filters as primary > queues. > > > > > > > Also, in order to know when it's ok to remove an event from the backup > > > queue, wouldn't this approach require maintaining a queue for each > > > connected client and having to deal with potentially unbounded queue > > > growth if a client struggles to keep up or simply stops acking? > > > > > > > I think the policy for backups should be no different as for the > primaries. > > As far as slow clients, Ignite is capable to automatically disconnect > them: > > http://s.apache.org/managing-slow-clients > > > > Isn't this feature getting Ignite into the murky waters of the message > > > brokers and guaranteed once-only message delivery with all the > complexity > > > and overhead that come with it? Besides in some cases, it's doesn't > really > > > matter if some updates are missing, while in others it is only > necessary to > > > be able to detect a missing update. I wouldn't want to have to pay for > > > something I don't need... > > > > > > > I believe that the new proposed approach will be optional and you will > > still be able to get event notifications in non-fault-tolerant manner the > > old way. > > > > > > > > > > Thanks > > > Andrey > > > > > > > Date: Fri, 24 Jul 2015 23:40:15 -0700 > > > > Subject: Re: Continuous queries changes > > > > From: valentin.kuliche...@gmail.com > > > > To: dev@ignite.incubator.apache.org > > > > > > > > Andrey, > > > > > > > > I mean the queue of update events that is collected on backup nodes > and > > > > flushed to listening clients in case of topology change. > > > > > > > > -Val > > > > > > > > On Fri, Jul 24, 2015 at 3:16 PM, Andrey Kornev < > andrewkor...@hotmail.com > > > > > > > > wrote: > > > > > > > > > Val, > > > > > > > > > > Could you please elaborate what you mean by "updates queue" you > plan to > > > > > maintain on the primary and backup nodes? > > > > > > > > > > Thanks > > > > > Andrey > > > > > > > > > > > Date: Fri, 24 Jul 2015 17:51:48 +0300 > > > > > > Subject: Re: Continuous queries changes > > > > > > From: yzhda...@apache.org > > > > > > To: dev@ignite.incubator.apache.org > > > > > > > > > > > > Val, > > > > > > > > > > > > I have idea on how to clean up backup queue. > > > > > > > > > > > > 1. Our communication uses acks. So, you can determine [on server > > > node] > > > > > > whether client received the update from local server or not. I > think > > > you > > > > > > can easily change existing code to get notifications on ack > receiving > > > > > (this > > > > > > way you dont need to introduce your own acks). > > > > > > 2. How do you know when evict from backup? Each message that > client > > > acks > > > > > > corresponds to some per-partition long value you talked above > (great > > > > > idea, > > > > > > btw!). Servers can exchange per-partition long value that > > > corresponds to > > > > > > the latest acked message and that's the way how backups can > safely > > > evict > > > > > > from the queue. > > > > > > > > > > > > Let me know if you have questions. > > > > > > > > > > > > --Yakov > > > > > > > > > > > > 2015-07-23 8:53 GMT+03:00 Valentin Kulichenko < > > > > > valentin.kuliche...@gmail.com > > > > > > >: > > > > > > > > > > > > > Igniters, > > > > > > > > > > > > > > Based on discussions with our users I came to conclusion that > our > > > > > > > continuous query implementation is not good enough for use > cases > > > with > > > > > > > strong consistency requirements, because there is a > possibility to > > > lose > > > > > > > updates in case of topology change. > > > > > > > > > > > > > > So I started working on > > > > > https://issues.apache.org/jira/browse/IGNITE-426 > > > > > > > and I hope to finish in in couple of weeks so that we can > include > > > it in > > > > > > > next release. > > > > > > > > > > > > > > I have the following design in mind: > > > > > > > > > > > > > > - Maintain updates queue on backup node(s) in addition to > > > primary > > > > > node. > > > > > > > - If primary node crushes, this queue is flushed to > listening > > > > > clients. > > > > > > > - To avoid notification duplicates we will have a > per-partition > > > > > update > > > > > > > counter. Once an entry in some partition is updated, > counter for > > > > > this > > > > > > > partition is incremented on both primary and backups. The > value > > > of > > > > > this > > > > > > > counter is also sent along with the update to the client, > which > > > also > > > > > > > maintains the copy of this mapping. If at some moment it > > > receives an > > > > > > > update > > > > > > > with the counter less than in its local map, this update is > a > > > > > duplicate > > > > > > > and > > > > > > > can be discarded. > > > > > > > - Also need to figure out the best way to clean the backup > > > queue if > > > > > > > topology is stable. Will be happy to hear any suggestions :) > > > > > > > > > > > > > > To make all this work we also need to implement > > > thread-per-partition > > > > > mode > > > > > > > in atomic cache, because now updates order on backup nodes can > > > differ > > > > > from > > > > > > > the primary node: > https://issues.apache.org/jira/browse/IGNITE-104 > > > . > > > > > I'm > > > > > > > already working on this. > > > > > > > > > > > > > > Feel free to share your thoughts! > > > > > > > > > > > > > > -Val > > > > > > > > > > > > > > > > > > > > > >
