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https://issues.apache.org/jira/browse/CASSANDRA-14744?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16613843#comment-16613843
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Benedict commented on CASSANDRA-14744:
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Have a look at
[ReplicaLayout.haveWriteConflicts|https://github.com/belliottsmith/cassandra/blob/7b7d0025c2470e69fa89053f8c9c9e25f5039941/src/java/org/apache/cassandra/locator/ReplicaLayout.java#L260]
from CASSANDRA-14705, which explains this.
Essentially, a transition is only used to consciously make the right choice at
write time. I hope in CASSANDRA-14666, we will begin caching the actual
layouts (or possibly even the plans themselves), at which point they'll not
even be seen.
TokenMetadata needs to be revisited as a whole, also, as brought up in
CASSANDRA-14660. At which point maybe we can also revisit how this
intermediate state tracks pending/natural.
> 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
> Priority: Major
> 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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