mck created CASSANDRA-15260:
-------------------------------
Summary: Add `allocate_tokens_for_dc_rf` yaml option for token
allocation
Key: CASSANDRA-15260
URL: https://issues.apache.org/jira/browse/CASSANDRA-15260
Project: Cassandra
Issue Type: Improvement
Components: Local/Config
Reporter: mck
Assignee: mck
Similar to option in DSE `allocate_tokens_for_local_replication_factor`
Currently the
[ReplicationAwareTokenAllocator|https://www.datastax.com/dev/blog/token-allocation-algorithm]
requires a defined keyspace and a replica factor specified in the current
datacenter.
This is problematic in a number of ways. Come version 4.0 the replica factor
can not be defined in new datacenters before those datacenters are up and
running. Previously even real keyspaces could not be used as a new datacenter
has to, in practice, have all its nodes up and running before it has the
capacity to replicate data into it. New datacenters, or lift-and-shifting a
cluster via datacenter migration, can be done using a dummy keyspace that
duplicates the replication strategy and factor of the real keyspace.
This issues are reduced by avoiding the keyspace definition and lookup, and
presuming the replica strategy is by datacenter, ie NTS, with the introduction
of an `allocate_tokens_for_dc_rf` option.
It may also be of value considering whether `allocate_tokens_for_dc_rf=3` is
the default, as this is the replication factor for the vast majority of
datacenters in production. I suspect this would be a good improvement over the
existing randomly generated tokens algorithm.
Initial patch is available in
https://github.com/thelastpickle/cassandra/commit/fc4865b0399570e58f11215565ba17dc4a53da97
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