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From "Michael Marth (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (OAK-1453) MongoMK failover support for replica sets (esp. shards)
Date Wed, 02 Apr 2014 13:51:17 GMT

     [ https://issues.apache.org/jira/browse/OAK-1453?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael Marth updated OAK-1453:
-------------------------------

    Priority: Major  (was: Critical)

> 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
>            Assignee: Thomas Mueller
>              Labels: production, resilience
>             Fix For: 0.20
>
>
> 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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