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https://issues.apache.org/jira/browse/ZOOKEEPER-1001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998546#comment-12998546
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Flavio Junqueira commented on ZOOKEEPER-1001:
---------------------------------------------

The problem of reading uncommitted entries is that the uncommitted entries may 
never be committed, and it may lead to inconsistencies in the system. Say that 
the writer writes entry n+1 to a single bookie and crashes before it is able to 
commit it. A concurrent reader may end up reading n+1, and a later client that 
recovers the ledger may end up reading up to n only. This might lead to 
inconsistencies in some use cases, perhaps not yours.

At the same time, your description sort of supports our preference for 
notifying outside bookkeeper. If your use case does not require it, then you 
may choose not to implement it.



  

> 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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