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https://issues.apache.org/jira/browse/KAFKA-615?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jay Kreps updated KAFKA-615:
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Attachment: KAFKA-615-v4.patch
Rebased patch to trunk.
> Avoid fsync on log segment roll
> -------------------------------
>
> Key: KAFKA-615
> URL: https://issues.apache.org/jira/browse/KAFKA-615
> Project: Kafka
> Issue Type: Bug
> Reporter: Jay Kreps
> Assignee: Neha Narkhede
> Attachments: KAFKA-615-v1.patch, KAFKA-615-v2.patch,
> KAFKA-615-v3.patch, KAFKA-615-v4.patch
>
>
> It still isn't feasible to run without an application level fsync policy.
> This is a problem as fsync locks the file and tuning such a policy so that
> the flushes aren't so frequent that seeks reduce throughput, yet not so
> infrequent that the fsync is writing so much data that there is a noticable
> jump in latency is very challenging.
> The remaining problem is the way that log recovery works. Our current policy
> is that if a clean shutdown occurs we do no recovery. If an unclean shutdown
> occurs we recovery the last segment of all logs. To make this correct we need
> to ensure that each segment is fsync'd before we create a new segment. Hence
> the fsync during roll.
> Obviously if the fsync during roll is the only time fsync occurs then it will
> potentially write out the entire segment which for a 1GB segment at 50mb/sec
> might take many seconds. The goal of this JIRA is to eliminate this and make
> it possible to run with no application-level fsyncs at all, depending
> entirely on replication and background writeback for durability.
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