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https://issues.apache.org/jira/browse/ZOOKEEPER-1413?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thawan Kooburat updated ZOOKEEPER-1413:
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    Attachment: ZOOKEEPER-1413.patch

Fix bug
                
> Use on-disk transaction log for learner sync up
> -----------------------------------------------
>
>                 Key: ZOOKEEPER-1413
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1413
>             Project: ZooKeeper
>          Issue Type: Improvement
>          Components: server
>    Affects Versions: 3.4.3
>            Reporter: Thawan Kooburat
>            Assignee: Thawan Kooburat
>            Priority: Minor
>              Labels: performance
>             Fix For: 3.5.0
>
>         Attachments: ZOOKEEPER-1413.patch, ZOOKEEPER-1413.patch, 
> ZOOKEEPER-1413.patch, ZOOKEEPER-1413.patch, ZOOKEEPER-1413.patch, 
> ZOOKEEPER-1413.patch
>
>
> Motivation:
> The learner syncs up with leader by retrieving committed log from the leader. 
> Currently, the leader only keeps 500 entries of recently committed log in 
> memory. If the learner falls behind more than 500 updates, the leader will 
> send the entire snapshot to the learner. 
> With the size of the snapshot for some of our Zookeeper deployments (~10G), 
> it is prohibitively expensive to send the entire snapshot over network. 
> Additionally, our Zookeeper may serve more than 4K updates per seconds. As a 
> result, a network hiccups for less than a second will cause the learner to 
> use snapshot transfer.
> Design:
> Instead of looking only at committed log in memory, the leader will also look 
> at transaction log on disk. The amount of transaction log kept on disk is 
> configurable and the current default is 100k. This will allow Zookeeper to 
> tolerate longer temporal network failure before initiating the snapshot 
> transfer.  
> Implementation:
> We plan to add interface to the persistence layer will can be use to retrieve 
> proposals from on-disk transaction log. These proposals can then be used to 
> send to the learner using existing protocol. 

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