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https://issues.apache.org/jira/browse/OAK-1453?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcel Reutegger resolved OAK-1453.
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Resolution: Won't Fix
Fix Version/s: (was: 1.6)
I'm resolving this issue as WONTFIX because the proposed behaviour is very
difficult and complex to implement property, confusing for an API consumer and
contradicts what was implemented for OAK-2592 and OAK-3554.
The recommended deployment is a replica set with at least three members and a
majority write concern. With this setup (even when using shards) a write will
only succeed when it is replicated to at least one secondary. This means a
successful write operation survives even a primary crash. With this deployment
the proposed rollback mechanism in Oak is not needed.
Even if such a rollback is desired from a backend POV, the consequences for an
Oak or JCR API consumer is rather dangerous and confusing because ACID
properties do not hold anymore.
> MongoMK failover support for replica sets (esp. shards)
> -------------------------------------------------------
>
> Key: OAK-1453
> URL: https://issues.apache.org/jira/browse/OAK-1453
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: mongomk
> Reporter: Michael Marth
> Labels: production, resilience
>
> With OAK-759 we have introduced replica support in MongoMK. I think we still
> need to address the resilience for failover from primary to secoandary:
> Consider a case where Oak writes to the primary. Replication to secondary is
> ongoing. During that period the primary goes down and the secondary becomes
> primary. There could be some "half-replicated" MVCC revisions, which need to
> be either discarded or be ignored after the failover.
> This might not be an issue if there is only one shard, as the commit root is
> written last (and replicated last)
> But with 2 shards the the replication state of these 2 shards could be
> inconsistent. Oak needs to handle such a situation without falling over.
> If we can detect a Mongo failover we could query Mongo which revisions are
> fully replicated to the new primary and discard the potentially
> half-replicated revisions.
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