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From "Shashikant Banerjee (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Deleted] (HDDS-1843) Undetectable corruption after restart of a datanode
Date Tue, 06 Aug 2019 13:39:00 GMT

     [ https://issues.apache.org/jira/browse/HDDS-1843?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Shashikant Banerjee updated HDDS-1843:
--------------------------------------
    Comment: was deleted

(was: Added an initial patch v0 to address the problem. The patch is rebased on top of HDDS-1610.
Will open a PR as soon as 1610 gets committed,)

> Undetectable corruption after restart of a datanode
> ---------------------------------------------------
>
>                 Key: HDDS-1843
>                 URL: https://issues.apache.org/jira/browse/HDDS-1843
>             Project: Hadoop Distributed Data Store
>          Issue Type: Bug
>          Components: Ozone Datanode
>    Affects Versions: 0.5.0
>            Reporter: Shashikant Banerjee
>            Assignee: Shashikant Banerjee
>            Priority: Critical
>             Fix For: 0.5.0
>
>         Attachments: HDDS-1843.000.patch
>
>
> Right now, all write chunks use BufferedIO ie, sync flag is disabled by default. Also,
Rocks Db metadata updates are done in Rocks DB cache first at Datanode. In case, there comes
a situation where the buffered chunk data as well as the corresponding metadata update is
lost as a part of datanode restart, it may lead to a situation where, it will not be possible
to detect the corruption (not even with container scanner) of this nature in a reasonable
time frame, until and unless there is a client IO failure or Recon server detects it over
time. In order to atleast to detect the problem, Ratis snapshot on datanode should sync the
rocks db file . In such a way, ContainerScanner will be able to detect this.We can also add
a metric around sync to measure how much of a throughput loss it can incurr.
> Thanks [~msingh] for suggesting this.



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