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https://issues.apache.org/jira/browse/ZOOKEEPER-1001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13000400#comment-13000400
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Benjamin Reed commented on ZOOKEEPER-1001:
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the time to get the rest of the ledgers will be dominated by the time to detect
the failure of the writer. for most applications you will already have
something in place for failure detection. for example, in the case of the
namenode, you will have a backup watching for the primary to die. when that
happens, the backup will simply reopen the ledger and allow recovery to take
place and read the last few entries. since it only needs to read the ones that
were committed during recovery, this will happen very fast.
> Read from open ledger
> ---------------------
>
> Key: ZOOKEEPER-1001
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1001
> Project: ZooKeeper
> Issue Type: New Feature
> Components: contrib-bookkeeper
> Reporter: Flavio Junqueira
>
> The BookKeeper client currently does not allow a client to read from an open
> ledger. That is, if the creator of a ledger is still writing to it (and the
> ledger is not closed), then an attempt to open the same ledger for reading
> will execute the code to recover the ledger, assuming that the ledger has not
> been correctly closed.
> It seems that there are applications that do require the ability to read from
> a ledger while it is being written to, and the main goal of this jira is to
> discuss possible implementations of this feature.
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