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Date: Fri, 17 Apr 2015 16:43:59 +0000 (UTC)
From: "Brandon Williams (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Updated] (CASSANDRA-9206) Remove seed gossip probability
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     [ https://issues.apache.org/jira/browse/CASSANDRA-9206?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Brandon Williams updated CASSANDRA-9206:
----------------------------------------
    Attachment: 9206.txt

> Remove seed gossip probability
> ------------------------------
>
>                 Key: CASSANDRA-9206
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9206
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Brandon Williams
>            Assignee: Brandon Williams
>             Fix For: 2.1.5
>
>         Attachments: 9206.txt
>
>
> Currently, we use probability to determine whether a node will gossip with a seed:
> {noformat} 
>                 double probability = seeds.size() / (double) (liveEndpoints.size() + unreachableEndpoints.size());
>                 double randDbl = random.nextDouble();
>                 if (randDbl <= probability)
>                     sendGossip(prod, seeds);
> {noformat}
> I propose that we remove this probability, and instead *always* gossip with a seed.  This of course means increased traffic and processing on the seed(s), but even a 1000 node cluster with a single seed will only put ~1000 messages per second on the seed, which is virtually nothing.  Should it become a problem, the solution is simple: add more seeds.  Since seeds will also always gossip with each other, this effectively gives us a poor man's spanning tree, with the only cost being removing a few lines of code, and should greatly improve our gossip convergence time, especially in large clusters.


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