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From "Utkarsh Srivastava (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ZOOKEEPER-462) Last hint for open ledger
Date Thu, 08 Oct 2009 17:55:31 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-462?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12763595#action_12763595

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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