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https://issues.apache.org/jira/browse/ZOOKEEPER-1001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998501#comment-12998501
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dhruba borthakur commented on ZOOKEEPER-1001:
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when a reader is reading data from a ledger that is being written to
concurrently, it should be fine even if the reader reads uncommitted data (i.e.
data that is not yet written to a quorum set of bookies). In fact, the reader
can go to any bookie and query how many records it currently have, and then
read all those records. This could mean that we do not need any notification
mechanism between the writer and concurrent-readers.
> 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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