[jira] [Commented] (HDFS-4397) Combined diff may not be identical to the diffs applied sequentially

["Tsz Wo (Nicholas), SZE (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-4397?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13552487#comment-13552487 ] 

Tsz Wo (Nicholas), SZE commented on HDFS-4397:
----------------------------------------------

In the case 3 of combinePostDiff, the nodes inserted to the c-list and the d-list may be incorrect.  The simplest way to fix it is to use modify(..) as stated in the algorithm (which is available in the javadoc.)
                
> Combined diff may not be identical to the diffs applied sequentially
> --------------------------------------------------------------------
>
>                 Key: HDFS-4397
>                 URL: https://issues.apache.org/jira/browse/HDFS-4397
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>
> Let diffs
> {noformat}
> d(1,k)   = m_1 + m_2 + ... + m_k;
> d(k+1,n) = m_{k+1} + m_{k+2} + ... + m_n;
> {noformat}
> and
> {noformat}
> d(1,n)   = m_1 + m_2 + ... + m_n,
> {noformat}
> where m_j denote modifications.  Then, we may have
> {noformat}
> d(1,k) + d(k+1,n) != d(1,n).
> {noformat}

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