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https://issues.apache.org/jira/browse/BOOKKEEPER-101?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ivan Kelly updated BOOKKEEPER-101:
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Attachment: BOOKKEEPER-101.diff
Addressed Dhruba's comments
> Add Fencing to Bookkeeper
> -------------------------
>
> Key: BOOKKEEPER-101
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-101
> Project: Bookkeeper
> Issue Type: New Feature
> Reporter: Ivan Kelly
> Assignee: Ivan Kelly
> Fix For: 4.0.0
>
> Attachments: BOOKKEEPER-101.diff, BOOKKEEPER-101.diff,
> BOOKKEEPER-101.diff, BOOKKEEPER-101.diff, BOOKKEEPER-101.diff
>
>
> BookKeeper is designed for use as a Write ahead log. In systems with a
> primary/backup architecture, the primary will write state updates to the WAL.
> If the primary dies the backup comes online, reads the WAL to get the latest
> state and starts serving requests. However, if the primary was only
> partitioned from the network, or stuck in a long GC, a split brain occurs.
> Both primary and backup can service client requests.
> Fencing(http://en.wikipedia.org/wiki/Fencing_%28computing%29) ensures that
> this cannot happen. With fencing, the backup can close the WAL of the
> primary, and cause any subsequent attempt by the primary to write to the WAL
> to give an error.
> We fence a ledger whenever it is opened by another client using
> BookKeeper#openLedger. BookKeeper#openLedgerNoRecovery will not fence.
> The opening client marks the ledger as fenced in zookeeper, and then sends a
> readEntry message to a all of bookies with the DO_FENCING flag set. Once at
> least 1 bookie in each possible quorum of bookies have responded, we can
> proceed with opening the ledger. Any subsequent attempt to write to the
> ledger will fail as it will not be able to write to a quorum without one of
> the bookie in the quorum responding with a ledger fenced error. The client
> will also be unable to change the quorum without seeing that the ledger has
> been marked as fenced in zookeeper.
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