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https://issues.apache.org/jira/browse/HDFS-1580?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13042313#comment-13042313
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Ivan Kelly commented on HDFS-1580:
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@Jitendra
(1) should work for checkpointing, as if you journal A has more edits than
journal B while counting the in_progress file, it will have more or an equal
number not counting the in_progress file. More in the case that B has gaps in
which case it throws an exception, equal otherwise.
So we finalise inprogress when we open a write and spot an inprogress file. I
guess this should only happen on startup after a crash. The writer shouldn't
finalise an inprogress if something else is writing to it. We have nothing to
prevent this now, but if this is happening, your system is broken. Fencing
could be implemented later to explicitly exclude this possibility.
> Add interface for generic Write Ahead Logging mechanisms
> --------------------------------------------------------
>
> Key: HDFS-1580
> URL: https://issues.apache.org/jira/browse/HDFS-1580
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Ivan Kelly
> Fix For: Edit log branch (HDFS-1073)
>
> Attachments: EditlogInterface.1.pdf, EditlogInterface.2.pdf,
> HDFS-1580+1521.diff, HDFS-1580.diff, HDFS-1580.diff, HDFS-1580.diff,
> generic_wal_iface.pdf, generic_wal_iface.pdf, generic_wal_iface.pdf,
> generic_wal_iface.txt
>
>
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