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https://issues.apache.org/jira/browse/KAFKA-77?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jay Kreps resolved KAFKA-77.
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    Resolution: Won't Fix

This is not really a good idea post 0.8 as we no longer have much dependence on 
the disk flush.
                
> Implement "group commit" for kafka logs
> ---------------------------------------
>
>                 Key: KAFKA-77
>                 URL: https://issues.apache.org/jira/browse/KAFKA-77
>             Project: Kafka
>          Issue Type: Improvement
>    Affects Versions: 0.7
>            Reporter: Jay Kreps
>            Assignee: Jay Kreps
>             Fix For: 0.8
>
>         Attachments: kafka-group-commit.patch
>
>
> The most expensive operation for the server is usually going to be the 
> fsync() call to sync data in a log to disk, if you don't flush your data is 
> at greater risk of being lost in a crash. Currently we give two knobs to tune 
> this trade--log.flush.interval and log.default.flush.interval.ms (no idea why 
> one has default and the other doesn't since they are both defaults). However 
> if you flush frequently, say on every write, then performance is not that 
> great.
> One trick that can be used to improve this worst case of continual flushes is 
> to allow a single fsync() to be used for multiple writes that occur at the 
> same time. This is a lot like "group commit" in databases. It is unclear 
> which cases this would improve and by how much but it might be worth a try.

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