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 >
