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https://issues.apache.org/jira/browse/ZOOKEEPER-1016?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13009152#comment-13009152
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Ivan Kelly commented on ZOOKEEPER-1016:
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As mahadev said, this does not replace logging to bookkeeper. Every update
written to the writer is written to the bookies and then only after it has been
committed to bookkeeper is it sent to the secondaries. How it is "sent" to the
secondaries is up for discussion. It could be sent directly, a signal could be
sent to the secondaries that updates are available at the ledger.
Regarding an API for named ledgers, this is the core of what TeaKeeper is, an
API around ZooKeeper and BookKeeper adding the concept of transactions to
logging to ledgers. The part about keeping secondaries up to date is just an
extension of this.
I'll update the doc to address all the comments here in the next day or two
hopefully.
> TeaKeeper: Hot standby support using bookkeeper
> -----------------------------------------------
>
> Key: ZOOKEEPER-1016
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1016
> Project: ZooKeeper
> Issue Type: Improvement
> Reporter: Ivan Kelly
> Assignee: Ivan Kelly
> Priority: Minor
> Attachments: tledger.pdf
>
>
> Currently Bookkeeper provides functionality for cold backups. If the entity
> logging to bookkeeper fails, its replacement must recover the ledgers which
> had been used for backup before becoming available. This is acceptable in
> some cases, such as HBase Wals where a small delay in recovery only results
> in a small percentage of data being unavailable.
> However, systems such as the HDFS namenode, this delay can be unacceptable,
> such as cases where data is being served to customers. Secondary namenodes
> should be ready to go the instant the primary goes down.
> TeaKeeper proposes a wrapper library around Bookkeeper providing T-Junction
> like functionality for logging. It also provides for primary/secondary
> election and automated hot failover.
> HDFS namenode is primary target of this work.
> The attached design doc contains more details.
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