Ariel Weisberg created CASSANDRA-14744:
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Summary: TR transient -> full and full -> transient enters pending
state reducing availability
Key: CASSANDRA-14744
URL: https://issues.apache.org/jira/browse/CASSANDRA-14744
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Ariel Weisberg
Fix For: 4.x
A transient replica transitioning to full and vice versa doesn't cease to be
the kind of replica it used to be before. I think this could cause availability
issues if a node goes down and it could even cause unavailable with some ring
movements with all nodes up. I haven't convinced myself 100% this is true, but
I think it should be possible to construct an example.
We can't read from pending replicas so if a ring movement were to make 2/3 out
of a group of 3 pending we would have this problem.
The key difference here is that the existing replica should be available during
this period as the kind of replica it was before. A full replica remains full
until nodetool cleanup is run. A transient replica remains transient the entire
time.
Obviously this doesn't hold for transitions to/from not replicated at all.
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