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From "Andrey Stepachev (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-10641) Introduce Coordination Engine
Date Thu, 12 Jun 2014 21:59:03 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-10641?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14029899#comment-14029899

Andrey Stepachev commented on HADOOP-10641:

[~zero45], good work. 
just a couple of picky notes :)

Not configured localNodeId can lead to uncontrolled creation of new zk sessions. 
Should code check that before creating ZooKeeper object?
'catch' should close zookeeper, if it was opened.

split doesn’t take into account chrooted zk configurations. 
it is much better to use org.apache.zookeeper.client.ConnectStringParser

currentGSN is long, but treated as integer. easy to create overflow.

More serious problem, that zk sequential nodes are _integer_.
Code should guard sequence overflows over zero and handle that using 
more then one parent znodes or zero crossing detection or other techniques 
preventing integer seqence id overflow.

> Introduce Coordination Engine
> -----------------------------
>                 Key: HADOOP-10641
>                 URL: https://issues.apache.org/jira/browse/HADOOP-10641
>             Project: Hadoop Common
>          Issue Type: New Feature
>    Affects Versions: 3.0.0
>            Reporter: Konstantin Shvachko
>            Assignee: Plamen Jeliazkov
>         Attachments: HADOOP-10641.patch, HADOOP-10641.patch, HADOOP-10641.patch
> Coordination Engine (CE) is a system, which allows to agree on a sequence of events in
a distributed system. In order to be reliable CE should be distributed by itself.
> Coordination Engine can be based on different algorithms (paxos, raft, 2PC, zab) and
have different implementations, depending on use cases, reliability, availability, and performance
> CE should have a common API, so that it could serve as a pluggable component in different
projects. The immediate beneficiaries are HDFS (HDFS-6469) and HBase (HBASE-10909).
> First implementation is proposed to be based on ZooKeeper.

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