Support multiple non-consecutive tokens per host (virtual nodes)
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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
This is the parent ticket for the virtual nodes implementation which was
proposed here:
http://www.mail-archive.com/[email protected]/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 IP 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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