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

["dhruba borthakur (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-2656?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

dhruba borthakur updated HADOOP-2656:
-------------------------------------

    Attachment: upgradeGenStamp4.patch

This patch does the following:

1. Upgrades existing clusters to the new disk format. Each Block has a generation stamp associated with it. Existing blocks get a generation stamp of 0. The generation stamp is used to create the name of the block metafile on the datanode.

2. The Block object has a new field called "generationStamp" of type "long". The BlocksMap on the namenode is keyed on the blockid and the generation stamp.

3. The datanode sends the generation stamp, block id and size of each block in a block report.

3. All log statements that print the blockid now prints the blockid and generationstamp.

4. The client receives the blockid and generation stamp as part of an RPC that receives a block. 

5. The DataTransferProtocol sends the blockid and generation stamp with every connection request that the client makes to the datanode(s).


> 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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