[jira] Commented: (HADOOP-2656) Support for upgrading existing cluster to facilitate appends to HDFS files

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

    [ https://issues.apache.org/jira/browse/HADOOP-2656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12589257#action_12589257 ] 

Tsz Wo (Nicholas), SZE commented on HADOOP-2656:
------------------------------------------------

upgradeGenStamp4.patch : 
- In Block.isBlockFilename(File f), it disallows file name containing "." but "." is used in Block.toString() in the new codes.  

- A constant BLOCK_FILE_PREFIX="blk_" is defined in DataStorage but not is used in other part of the codes.

- Another METADATA_EXTENSION=".meta" is defined in FSDataset, you should not define a new one in BlockMetadata

We have to be careful about handling the filenames for blocks and meta data.  It would be better if we put all the codes in one place.

> Support for upgrading existing cluster to facilitate appends to HDFS files
> --------------------------------------------------------------------------
>
>                 Key: HADOOP-2656
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2656
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: upgradeGenStamp4.patch
>
>
> HADOOP-1700 describes the design for supporting appends to HDFS files. This design requires a distributed-upgrade to existing cluster installations. The design specifies that the DataNode persist the 8-byte BlockGenerationStamp in the block metadata file. The upgrade code will introduce this new field in the block metadata file and initialize this value to 0.

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