Utkarsh Srivastava commented on ZOOKEEPER-462:

Ben and I discussed this and we dont think this is the best design. Under the 
current design, a lot of unnecessary write load will be put on ZK. 

Instead, the bookies already support a method to query for the last entry for a 
particular ledger. Thus, a client that wants to read an unclosed ledger can ask 
the bookies for their last entries and read until there. 

> Last hint for open ledger
> -------------------------
>                 Key: ZOOKEEPER-462
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-462
>             Project: Zookeeper
>          Issue Type: New Feature
>          Components: contrib-bookkeeper
>            Reporter: Flavio Paiva Junqueira
>            Assignee: Flavio Paiva Junqueira
>             Fix For: 3.3.0
>         Attachments: ZOOKEEPER-462.patch
> In some use cases of BookKeeper, it is useful to be able to read from a 
> ledger before closing the ledger. To enable such a feature, the writer has to 
> be able to communicate to a reader how many entries it has been able to write 
> successfully. The main idea of this jira is to continuously update a znode 
> with the number of successful writes, and a reader can, for example, watch 
> the node for changes.
>  I was thinking of having a configuration parameter to state how often a 
> writer should update the hint on ZooKeeper (e.g., every 1000 requests, every 
> 10,000 requests). Clearly updating more often increases the overhead of 
> writing to ZooKeeper, although the impact on the performance of writes to 
> BookKeeper should be minimal given that we make an asynchronous call to 
> update the hint.

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