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From "Branimir Lambov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12777) Optimize the vnode allocation for single replica per DC
Date Mon, 17 Oct 2016 10:51:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12777?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15581880#comment-15581880
] 

Branimir Lambov commented on CASSANDRA-12777:
---------------------------------------------

Thank you for the changes, this looks good to me.

One last thing is bothering me about the takeover situation (and sorry I did not get around
to writing about it earlier): in greater-than we set to 0.75, but [on equal (or close to equal)
we let the new take completely over|https://github.com/DikangGu/cassandra/commit/402050e32732e67055935689951a56f92b9be281#diff-3ee50470ce492c51246b32b35fae5cfcR198].
This feels inconsistent and (at least to me) potentially problematic (it may also be the reason
why we see no effect on the simulation). Could we limit the fraction of the range that can
be taken over instead?

> Optimize the vnode allocation for single replica per DC
> -------------------------------------------------------
>
>                 Key: CASSANDRA-12777
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12777
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Dikang Gu
>            Assignee: Dikang Gu
>             Fix For: 3.x
>
>
> The new vnode allocation algorithm introduced in CASSANDRA-7032 is optimized for the
situation that there are multiple replicas per DC.
> In our production environment, most cluster only has one replica, in this case, the algorithm
does not work perfectly. It always tries to split token ranges by half, so that the ownership
of "min" node could go as low as ~60% compared to avg.
> So for single replica case, I'm working on a new algorithm, which is based on Branimir's
previous commit, to split token ranges by "some" percentage, instead of always by half. In
this way, we can get a very small variation of the ownership among different nodes.



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