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https://issues.apache.org/jira/browse/HDFS-3540?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13447093#comment-13447093
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Tsz Wo (Nicholas), SZE commented on HDFS-3540:
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{quote}
I want to emphasize one thing here: UNCHECKED_REGION_LENGTH is not part of
Recovery Mode. If you look at the history FSEditLog.java, you'll see that
change 1325075 (HDFS-3055) introduced Recovery mode, but not
UNCHECKED_REGION_LENGTH. This was introduced in HDFS-3479 (the backport of
HDFS_3335 to branch-1). ...
{quote}
Correct me if I am wrong: Recovery Mode without HDFS-3479 means the entire
end-of-log is not checked and, therefore, the silent data loss length is not
limited. It is even worst.
The only feature in branch-1 Recovery Mode is to let user to choose "stop
reading" or "quit without saving". "Stop reading" may lead to silent data
loss. "Quit without saving" is the same as NN failing to start up. Thus, I
suggest to remove branch-1 Recovery Mode
{quote}
The padding length is going to be a megabyte at most. Since the edit log files
are fairly large, you should have a good idea of what percentage through the
file you are. ...
{quote}
A megabyte could contain hundreds or thousands of edit log transactions. It is
catastrophic in production clusters. Also, the percentage here may not be
relevant since the transactions at the end are the latest transactions and,
very likely, are the most important transactions.
> Further improvement on recovery mode and edit log toleration in branch-1
> ------------------------------------------------------------------------
>
> Key: HDFS-3540
> URL: https://issues.apache.org/jira/browse/HDFS-3540
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 1.2.0
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> *Recovery Mode*: HDFS-3479 backported HDFS-3335 to branch-1. However, the
> recovery mode feature in branch-1 is dramatically different from the recovery
> mode in trunk since the edit log implementations in these two branch are
> different. For example, there is UNCHECKED_REGION_LENGTH in branch-1 but not
> in trunk.
> *Edit Log Toleration*: HDFS-3521 added this feature to branch-1 to remedy
> UNCHECKED_REGION_LENGTH and to tolerate edit log corruption.
> There are overlaps between these two features. We study potential further
> improvement in this issue.
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