Kurt Greaves created CASSANDRA-13841:
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Summary: Allow specific sources during rebuild
Key: CASSANDRA-13841
URL: https://issues.apache.org/jira/browse/CASSANDRA-13841
Project: Cassandra
Issue Type: Bug
Reporter: Kurt Greaves
Assignee: Kurt Greaves
Priority: Minor
CASSANDRA-10406 introduced the ability to rebuild specific ranges, and
CASSANDRA-9875 extended that to allow specifying a set of hosts to stream from.
It's not incredibly clear why you would only want to stream a subset of ranges,
but a possible use case for this functionality is to rebuild a node from
targeted replicas.
When doing a DC migration, if you are using racks==RF while rebuilding you can
ensure you rebuild from each copy of a replica in the source datacenter by
specifying all the hosts from a single rack to rebuild a single copy from. This
can be repeated for each rack in the new datacenter to ensure you have each
copy of the replica from the source DC, and thus maintaining consistency
through rebuilds.
For example, with the following topology for DC A and B with an RF of A:3 and
B:3
||A|||| ||B||
||Node||Rack||Node||Rack||
|A1|rack1| B1|rack1|
|A2|rack2| B2|rack2|
|A3|rack3| B3|rack3|
The following set of actions will result in having exactly 1 copy of every
replica in A in B, and B will be _at least_ as consistent as A.
Rebuild B1 from only A1
Rebuild B2 from only A2
Rebuild B3 from only A3
Unfortunately using this functionality is non-trivial at the moment, as you can
only specify specific sources WITH the nodes set of tokens to rebuild from. To
perform the above with vnodes/a large cluster, you will have to specify every
token range in the -ts arg, which quickly gets unwieldy/impossible if you have
a large cluster.
A solution to this is to simply filter on sources first, before processing
ranges.
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