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From "Jay Kreps (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (KAFKA-615) Avoid fsync on log segment roll
Date Mon, 03 Mar 2014 17:41:21 GMT

     [ https://issues.apache.org/jira/browse/KAFKA-615?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Jay Kreps updated KAFKA-615:

    Issue Type: New Feature  (was: Bug)

> Avoid fsync on log segment roll
> -------------------------------
>                 Key: KAFKA-615
>                 URL: https://issues.apache.org/jira/browse/KAFKA-615
>             Project: Kafka
>          Issue Type: New Feature
>            Reporter: Jay Kreps
>            Assignee: Jay Kreps
>             Fix For: 0.8.1
>         Attachments: KAFKA-615-v1.patch, KAFKA-615-v2.patch, KAFKA-615-v3.patch, KAFKA-615-v4.patch,
KAFKA-615-v5.patch, KAFKA-615-v6.patch, KAFKA-615-v7.patch, KAFKA-615-v8.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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