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https://issues.apache.org/jira/browse/QPID-2220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12850901#action_12850901
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Alan Conway commented on QPID-2220:
-----------------------------------
As of r916475, the last survivor in a cluster automatically marks its store as
clean, so the only way we can end up with no clean store is if N>1 members fail
so close together that none of them receives a config-change showing them to be
the last member. For that we need a counter from the store as described above.
> Assisting manual recovery from a complete persistent cluster crash.
> -------------------------------------------------------------------
>
> Key: QPID-2220
> URL: https://issues.apache.org/jira/browse/QPID-2220
> Project: Qpid
> Issue Type: Improvement
> Components: C++ Broker
> Affects Versions: 0.5
> Reporter: Alan Conway
> Assignee: Alan Conway
>
> If every member of a persistent cluster crashes then manual intervention is
> required to identify which store is most up-to-date, so it can be used to
> recover. We need to provide tools to assist in this identification.
> The cluster can save a config-change counter with each config change (cluster
> membership change). In recovery, the broker with the highest config-change
> counter has the best store.
> However if the last brokers in the cluster crash so close together that none
> can record a config-change we need an additional decider.
> The store at http://qpidcomponents.org/download.html#persistence maintains a
> global Persistence ID, a 64 bit value that is incremented for each enqueue,
> dequeue. If the cluster stores (config-change,PID) pairs then in recovery we
> can use actual-PID - config-change PID as a tiebreaker.
> Proposed change to MessageStore API:
> /** Returns a monotonically increasing value reflecting changes to the
> store.
> * The value can wrap-around to 0.
> * Stores need not implement this function, they can simply return 0.
> */
> uint64_t getChangeCounter();
> The default implementation just returns 0 and the cluster must fall back to
> relying on config-change counts.
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