Abmar Barros commented on ZOOKEEPER-702:

While refactoring the server side of the server-client monitoring, more 
specifically the SessionTracking related classes, I realized that, once the 
servers do not ping the clients, and they also use app messages received from 
the clients as heartbeats, it is not possible to do an adaptive monitoring of 
the clients. Servers do not know the time a client sends a ping and pings are 
not sent frequently -- only at idle intervals.

I am finishing refactoring the server side code and I will force the use of a 
fixed heartbeat strategy for now.

Comments and suggestions are welcome

> GSoC 2010: Failure Detector Model
> ---------------------------------
>                 Key: ZOOKEEPER-702
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-702
>             Project: Zookeeper
>          Issue Type: Wish
>            Reporter: Henry Robinson
>            Assignee: Abmar Barros
>         Attachments: bertier-pseudo.txt, bertier-pseudo.txt, chen-pseudo.txt, 
> chen-pseudo.txt, phiaccrual-pseudo.txt, phiaccrual-pseudo.txt, 
> ZOOKEEPER-702.patch, ZOOKEEPER-702.patch, ZOOKEEPER-702.patch
> Failure Detector Module
> Possible Mentor
> Henry Robinson (henry at apache dot org)
> Requirements
> Java, some distributed systems knowledge, comfort implementing distributed 
> systems protocols
> Description
> ZooKeeper servers detects the failure of other servers and clients by 
> counting the number of 'ticks' for which it doesn't get a heartbeat from 
> other machines. This is the 'timeout' method of failure detection and works 
> very well; however it is possible that it is too aggressive and not easily 
> tuned for some more unusual ZooKeeper installations (such as in a wide-area 
> network, or even in a mobile ad-hoc network).
> This project would abstract the notion of failure detection to a dedicated 
> Java module, and implement several failure detectors to compare and contrast 
> their appropriateness for ZooKeeper. For example, Apache Cassandra uses a 
> phi-accrual failure detector (http://ddsg.jaist.ac.jp/pub/HDY+04.pdf) which 
> is much more tunable and has some very interesting properties. This is a 
> great project if you are interested in distributed algorithms, or want to 
> help re-factor some of ZooKeeper's internal code.

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