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From "Nick Bailey (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-4658) NTS/RackAwareness doesn't work with vnodes
Date Wed, 12 Sep 2012 17:32:08 GMT
Nick Bailey created CASSANDRA-4658:

             Summary: NTS/RackAwareness doesn't work with vnodes
                 Key: CASSANDRA-4658
             Project: Cassandra
          Issue Type: Bug
    Affects Versions: 1.2.0 beta 1
            Reporter: Nick Bailey
             Fix For: 1.2.0

It doesn't look like the current vnode placement strategy will work with people using NTS
and multiple racks.

For reasons also described on CASSANDRA-3810, using racks and NTS requires tokens to alternate
racks around the ring in order to get an even distribution of data. The current solution for
upgrading/placing vnodes won't take this into account and will likely generate some hotspots
around the ring. 

Not sure what the best solution is. The two immediately obvious approaches appear to be quite
complicated at first.

* Fixing NTS to remove the requirement for rack ordering
** No idea how this would be accomplished
** Presents challenges for people upgrading. Would need to deprecate NTS for a new strategy
that replaces it, then have a clear upgrade path to that strategy which would need to be in
a pre 1.2 release.
* Changing vnode placement strategy
** Ordering vnodes would require quite a bit of additional logic. Adding a new node or rack
would also need to maintain ordering which could cause enough data movement to remove any
benefits vnodes have already.
** We could potentially adjust vnode token placement to offset any imbalances caused by NTS
but this would require a fairly intelligent mechanism for determining vnode placement. 

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