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From "Alexander Shraer (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ZOOKEEPER-1355) Add zk.updateServerList(newServerList)
Date Mon, 27 Feb 2012 04:51:49 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-1355?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Alexander Shraer updated ZOOKEEPER-1355:

    Attachment: ZOOKEEPER-1355-ver9-1.patch

small javadoc fix. see comment for ZOOKEEPER-1355-ver9.patch
> Add zk.updateServerList(newServerList) 
> ---------------------------------------
>                 Key: ZOOKEEPER-1355
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1355
>             Project: ZooKeeper
>          Issue Type: New Feature
>          Components: java client
>            Reporter: Alexander Shraer
>            Assignee: Alexander Shraer
>             Fix For: 3.5.0
>         Attachments: ZOOKEEPER-1355-ver2.patch, ZOOKEEPER-1355-ver4.patch, ZOOKEEPER-1355-ver5.patch,
ZOOKEEPER-1355-ver6.patch, ZOOKEEPER-1355-ver7.patch, ZOOKEEPER-1355-ver8.patch, ZOOKEEPER-1355-ver9-1.patch,
ZOOKEEPER-1355-ver9.patch, ZOOKEEPER=1355-ver3.patch, ZOOOKEEPER-1355-test.patch, ZOOOKEEPER-1355-ver1.patch,
ZOOOKEEPER-1355.patch, loadbalancing-more-details.pdf, loadbalancing.pdf
> When the set of servers changes, we would like to update the server list stored by clients
without restarting the clients.
> Moreover, assuming that the number of clients per server is the same (in expectation)
in the old configuration (as guaranteed by the current list shuffling for example), we would
like to re-balance client connections across the new set of servers in a way that a) the number
of clients per server is the same for all servers (in expectation) and b) there is no excessive/unnecessary
client migration.
> It is simple to achieve (a) without (b) - just re-shuffle the new list of servers at
every client. But this would create unnecessary migration, which we'd like to avoid.
> We propose a simple probabilistic migration scheme that achieves (a) and (b) - each client
locally decides whether and where to migrate when the list of servers changes. The attached
document describes the scheme and shows an evaluation of it in Zookeeper. We also implemented
re-balancing through a consistent-hashing scheme and show a comparison. We derived the probabilistic
migration rules from a simple formula that we can also provide, if someone's interested in
the proof.

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