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https://issues.apache.org/jira/browse/CASSANDRA-7306?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15098739#comment-15098739
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Jeff Jirsa commented on CASSANDRA-7306:
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[~jbellis] - that was one of my open questions where I asked [~tupshin] for
clarification.
As implemented (the way I would expect it to work as an operator), if a DC is
not gossipable, it's not available for requests. For that reason, we remove it
from the Map of datacenters in NTS, and the non-gossipable replicas will not
receive the mutation, and will not be counted towards CL calculations.
https://github.com/jeffjirsa/cassandra/blob/cassandra-7306/src/java/org/apache/cassandra/locator/NetworkTopologyStrategy.java#L69-L72
If the DC topology provider changes (adds/removes DCs from its
white/blacklist), it will re-instantiate the replication strategy to propagate
those changes:
https://github.com/jeffjirsa/cassandra/blob/cassandra-7306/src/java/org/apache/cassandra/db/Keyspace.java#L332-L339
> Support "edge dcs" with more flexible gossip
> --------------------------------------------
>
> Key: CASSANDRA-7306
> URL: https://issues.apache.org/jira/browse/CASSANDRA-7306
> Project: Cassandra
> Issue Type: Improvement
> Components: Distributed Metadata
> Reporter: Tupshin Harper
> Assignee: Jeff Jirsa
> Labels: ponies
>
> As Cassandra clusters get bigger and bigger, and their topology becomes more
> complex, there is more and more need for a notion of "hub" and "spoke"
> datacenters.
> One of the big obstacles to supporting hundreds (or thousands) of remote dcs,
> is the assumption that all dcs need to talk to each other (and be connected
> all the time).
> This ticket is a vague placeholder with the goals of achieving:
> 1) better behavioral support for occasionally disconnected datacenters
> 2) explicit support for custom dc to dc routing. A simple approach would be
> an optional per-dc annotation of which other DCs that DC could gossip with.
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