[jira] [Commented] (KAFKA-3968) fsync() is not called on parent directory when new FileMessageSet is flushed to disk

["Jun Rao (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3968?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17344701#comment-17344701 ] 

Jun Rao commented on KAFKA-3968:
--------------------------------

Merged the reworked PR [https://github.com/apache/kafka/pull/10680] to trunk.

> fsync() is not called on parent directory when new FileMessageSet is flushed to disk
> ------------------------------------------------------------------------------------
>
>                 Key: KAFKA-3968
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3968
>             Project: Kafka
>          Issue Type: Bug
>          Components: log
>    Affects Versions: 0.9.0.1, 0.10.0.0
>         Environment: Linux, ext4 filesystem
>            Reporter: Andrey Neporada
>            Assignee: Cong Ding
>            Priority: Major
>              Labels: reliability
>             Fix For: 3.0.0
>
>
> Kafka does not call fsync() on directory when new log segment is created and flushed to disk.
> The problem is that following sequence of calls doesn't guarantee file durability: 
> fd = open("log", O_RDWR | O_CREATE); // suppose open creates "log"
> write(fd);
> fsync(fd);
> If system crashes after fsync() but before parent directory have been flushed to disk, the log file can disappear.
> This is true at least for ext4 on Linux.
> Proposed solution is to flush directory when flush() is called for the first time.



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