Nick Bailey created CASSANDRA-4658:
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Summary: NTS/RackAwareness doesn't work with vnodes
Key: CASSANDRA-4658
URL: https://issues.apache.org/jira/browse/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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