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Tsz Wo Nicholas Sze commented on HDFS-3107: ------------------------------------------- Checked the design doc. It looks quite good. Just a minor comment below: {quote} Current implementation of snapshots does not require moving any data. Both approaches 2 and 3 mean that this property will be lost. Some data will need to be moved for the snapshots to work with truncates and appends. {quote} Even with truncate, snapshot creation does not require moving data. The data movement happens at truncate time. Is it correct? > HDFS truncate > ------------- > > Key: HDFS-3107 > URL: https://issues.apache.org/jira/browse/HDFS-3107 > Project: Hadoop HDFS > Issue Type: New Feature > Components: datanode, namenode > Reporter: Lei Chang > Assignee: Plamen Jeliazkov > Attachments: HDFS-3107.patch, HDFS-3107.patch, HDFS-3107.patch, > HDFS-3107.patch, HDFS-3107.patch, HDFS_truncate.pdf, HDFS_truncate.pdf, > HDFS_truncate_semantics_Mar15.pdf, HDFS_truncate_semantics_Mar21.pdf, > editsStored > > Original Estimate: 1,344h > Remaining Estimate: 1,344h > > Systems with transaction support often need to undo changes made to the > underlying storage when a transaction is aborted. Currently HDFS does not > support truncate (a standard Posix operation) which is a reverse operation of > append, which makes upper layer applications use ugly workarounds (such as > keeping track of the discarded byte range per file in a separate metadata > store, and periodically running a vacuum process to rewrite compacted files) > to overcome this limitation of HDFS. -- This message was sent by Atlassian JIRA (v6.3.4#6332)