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https://issues.apache.org/jira/browse/JAMES-3428?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benoit Tellier closed JAMES-3428.
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Resolution: Fixed
> Read repairs - Mailbox counters
> -------------------------------
>
> Key: JAMES-3428
> URL: https://issues.apache.org/jira/browse/JAMES-3428
> Project: James Server
> Issue Type: Improvement
> Components: cassandra, mailbox
> Reporter: Benoit Tellier
> Priority: Major
> Fix For: 3.6.0
>
>
> = Why?
> Mailbox conters inconsistencies requires manual intervention of the admin
> (via the solve-inconsistency webadmin endpoint) to be resolved.
> Having such task to ensure a correct denormalisation state is desirable, but
> optimally we should not have to rely on the admin to remember running it.
> We would prefer an auto-healing solution.
> Mailbox counters consistency had been a blocker for some of our existing
> deployments.
> = Context
> Read repair is a classic mechanism in eventual consistent databases (like
> cassandra) to piggy back consistency healing operation upon reads.
> A fraction of the reads will have a wider reach, read more data, and ensure
> it is correctly replicated.
> Cassandra eventual consistency is all about "replication", but
> "denormalization" consistency needs to be handled at the applicative layer.
> In the past we did set up "Solve inconsistency" tasks that can be assimilated
> to Cassandra repairs. In order to achieve denormalization auto-healing, we
> thus needs to implement "applicative read repairs".
> = Technically speaking
> Upon reads, for each mailbox, the mailbox mapper have a configurable random
> chance to trigger read repairs.
> In this case we reaqd the counters, and iterate counters metadata, and the
> "solve inconsistency" mechanism is applied, if needed.
> Write unit tests demonstrating this "solve inconsistency" behavior.
> Given that reading "all messages metadata" can be an expensive operation, we
> want to be running the repair asynchronously, in the background.
> = Definition Of Done
> Record a video : In a webmail ...
> - Given a read repair chance of 0.2 (20%)
> - There is a mailbox counter inconsistency inconsistency (10 mails unread in
> the mailbox but the counter display 26) - (use cqlsh to alter the value of
> the mailbox counter to something invalid)
> - The user does several reads - after some time, the inconsistency is fixed:
> The count of unread mails is 10!
> As an admin, I should be able to configure (or disable) the
> read-repair-chance for the mailbox entity
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