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From "Brandon Williams (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4119) Support multiple non-consecutive tokens per host (virtual nodes)
Date Wed, 20 Jun 2012 22:41:42 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13397959#comment-13397959
] 

Brandon Williams commented on CASSANDRA-4119:
---------------------------------------------

bq. You're testing from p/4127/01_migration_path?

Yes

bq. How many nodes in your test?

Three

bq. what test parameters did you use?

Just defaults with the thread count upped to 300 (separate stress machine)

bq. How many tokens per node are you using?

Default; 64

bq. Did you manually assign them or did you allow them to be selected automatically

Automatic.

bq. are they evenly distributed (hint: nodetool clusterinfo))?

The largest discrepancy I saw was about 6%, but even at 1-2% the difference was still profound.
                
> Support multiple non-consecutive tokens per host (virtual nodes)
> ----------------------------------------------------------------
>
>                 Key: CASSANDRA-4119
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4119
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Sam Overton
>            Assignee: Sam Overton
>              Labels: virtualnodes, vnodes
>
> This is the parent ticket for the virtual nodes implementation which was proposed here:
http://www.mail-archive.com/dev@cassandra.apache.org/msg03837.html and discussed in the subsequent
thread.
> The goals of this ticket are:
> * reduced operations complexity for scaling up/down
> * reduced rebuild time in event of failure
> * evenly distributed load impact in the event of failure
> * evenly distributed impact of streaming operations
> * more viable support for heterogeneity of hardware
> The intention is that this can be done in a way which is
> * fully backwards-compatible
> * optionally enabled
> The latter of these can be trivially achieved by setting the number of tokens per host
to 1, to reproduce the existing behaviour.
> Implementation detail can be added and discussed in the sub-tickets, but here is an overview
of the proposed changes:
> * TokenMetadata will allow multiple tokens per host
> * Hosts will be referred to by a UUID instead of token (e.g. in Gossip, when storing
hints, etc.)
> * A bootstrapping node can get multiple tokens from initial_token (comma separated) or
by random allocation
> * NetworkTopologyStrategy will be extended to be aware of virtual nodes so that replicas
are not placed on the same host (similar to racks now)
> * Repairs will be staggered similar to CASSANDRA-3721
> * Nodetool operations will be virtual-node aware, while maintaining backwards compatibility
(ie. existing scripts won't have to change)
> * Upgrade will be a standard rolling upgrade, with optional rolling migration to full
vnode support

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