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https://issues.apache.org/jira/browse/HDFS-7056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14201410#comment-14201410
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Plamen Jeliazkov commented on HDFS-7056:
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Regarding (4), I see two issues right now.
INodeFile.diskspaceConsumed() has always done its calculation based on the
current INodeFile blocks list. Prior to truncate, it was assumed the file only
grew, so diskspaceConsumed was always correct based on the current INodeFile
blocks list. With truncate now, especially with copy-on-truncate and certain
blocks living only in Snapshot diffs, diskspaceConsumed becomes a question.
Is INodeFile.diskspaceConsumed() meant to only return the disk space consumed
of just the current/latest INodeFile (as it currently does)? Or should it go
through its diffs and return the disk space consumed of all blocks that belong
to this BlockCollection?
I could not find any documentation for diskspaceConsumed() method.
Based on the code I see in INodeFile.computeContentSummary4Snapshot(), it seems
Snapshot diffs are only calculated towards disk space when the latest INodeFile
has been deleted. The disk space consumed calculation falls back to the last
diff that was known about.
> Snapshot support for truncate
> -----------------------------
>
> Key: HDFS-7056
> URL: https://issues.apache.org/jira/browse/HDFS-7056
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Konstantin Shvachko
> Assignee: Plamen Jeliazkov
> Attachments: HDFS-3107-HDFS-7056-combined.patch, HDFS-7056.patch,
> HDFS-7056.patch, HDFSSnapshotWithTruncateDesign.docx
>
>
> Implementation of truncate in HDFS-3107 does not allow truncating files which
> are in a snapshot. It is desirable to be able to truncate and still keep the
> old file state of the file in the snapshot.
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