[jira] [Created] (ZOOKEEPER-2003) Missing fsync() on the logs parent directory

["Samer Al-Kiswany (JIRA)" <ji...@apache.org>]

Samer Al-Kiswany created ZOOKEEPER-2003:
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             Summary: Missing fsync() on the logs parent directory
                 Key: ZOOKEEPER-2003
                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2003
             Project: ZooKeeper
          Issue Type: Bug
    Affects Versions: 3.4.6
            Reporter: Samer Al-Kiswany


After studying the steps ZooKeeper takes to update the logs we found the following bug. The bug may not manifest in the current file system implementations, but it violates the POSIX recommendations and may be an issue in some file systems.

Looking at the strace of zookeeper we see the following:
mkdir(v)
create(v/log)
append(v/log)
trunk(v/log) to almost 64MBs
write(v/log)  1 byte
fdatasync(v/log)

Although the data is fdatasynced to the log, the parent directory was never fsynced, consequently in case of a crash, the parent directory or the log file may be lost, as the parent directory and file metadata were never persisted on disk.
To be safe, both the log directory, and parent directory of the log directory should be fsynced as well.



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