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 > > > > > > > > > > > >
