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Date: Wed, 4 Dec 2013 01:02:45 +0000 (UTC)
From: "Jing Zhao (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12682212.1386014646588.66915.1386118965264@arcas>
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References: <JIRA.12682212.1386014646588@arcas>
Subject: [jira] [Commented] (HDFS-5590) Block ID and generation stamp may be
 reused when persistBlocks is set to false
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    [ https://issues.apache.org/jira/browse/HDFS-5590?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13838427#comment-13838427 ] 

Jing Zhao commented on HDFS-5590:
---------------------------------

Hi Konstantin, currently the property is not documented in hdfs-default.xml and is just defined in DFSConfigKeys for internal usage, so there is no way to deprecate the property. If we decide to always persist blocks, I think we should completely remove the property.

> Block ID and generation stamp may be reused when persistBlocks is set to false
> ------------------------------------------------------------------------------
>
>                 Key: HDFS-5590
>                 URL: https://issues.apache.org/jira/browse/HDFS-5590
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.2.0
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>         Attachments: HDFS-5590.000.patch, HDFS-5590.001.patch
>
>
> In a cluster with non-HA setup and dfs.persist.blocks set to false, we may have data loss in the following case:
> # client creates file1 and requests a block from NN and get blk_id1_gs1
> # client writes blk_id1_gs1 to DN
> # NN is restarted and because persistBlocks is false, blk_id1_gs1 may not be persisted in disk
> # another client creates file2 and NN will allocate a new block using the same block id blk_id1_gs1 since block ID and generation stamp are both increased sequentially.
> Now we may have two versions (file1 and file2) of the blk_id1_gs1 (same id, same gs) in the system. It will case data loss.


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