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From "Manoj Govindassamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11382) Persist Erasure Coding Policy ID in a new optional field in INodeFile in FSImage
Date Fri, 03 Feb 2017 21:37:52 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15852155#comment-15852155
] 

Manoj Govindassamy commented on HDFS-11382:
-------------------------------------------

Test failures doesn't look related to patch. All failed tests are passing locally for me,
with the patch. 

> Persist Erasure Coding Policy ID in a new optional field in INodeFile in FSImage
> --------------------------------------------------------------------------------
>
>                 Key: HDFS-11382
>                 URL: https://issues.apache.org/jira/browse/HDFS-11382
>             Project: Hadoop HDFS
>          Issue Type: Task
>          Components: hdfs
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Manoj Govindassamy
>            Assignee: Manoj Govindassamy
>         Attachments: HDFS-11382.01.patch
>
>
> For Erasure Coded files, replication field in INodeFile message is re-used  to store
the EC Policy ID. 
> *FSDirWriteFileOp#addFile*
> {noformat}
>   private static INodesInPath addFile(
>       FSDirectory fsd, INodesInPath existing, byte[] localName,
>       PermissionStatus permissions, short replication, long preferredBlockSize,
>       String clientName, String clientMachine)
>       throws IOException {
>     .. .. ..
>     try {
>       ErasureCodingPolicy ecPolicy = FSDirErasureCodingOp.
>           getErasureCodingPolicy(fsd.getFSNamesystem(), existing);
>       if (ecPolicy != null) {
>         replication = ecPolicy.getId();   <===
>       }
>       final BlockType blockType = ecPolicy != null?
>           BlockType.STRIPED : BlockType.CONTIGUOUS;
>       INodeFile newNode = newINodeFile(fsd.allocateNewInodeId(), permissions,
>           modTime, modTime, replication, preferredBlockSize, blockType);
>       newNode.setLocalName(localName);
>       newNode.toUnderConstruction(clientName, clientMachine);
>       newiip = fsd.addINode(existing, newNode, permissions.getPermission());
> {noformat}
> With HDFS-11268 fix, {{FSImageFormatPBINode#Loader#loadInodeFile}} is rightly getting
the EC ID from the replication field and then uses the right Policy to construct the blocks.
> *FSImageFormatPBINode#Loader#loadInodeFile*
> {noformat}
>       ErasureCodingPolicy ecPolicy = (blockType == BlockType.STRIPED) ?
>           ErasureCodingPolicyManager.getPolicyByPolicyID((byte) replication) :
>           null;
> {noformat}
> The original intention was to re-use the replication field so the in-memory representation
would be compact. But, this isn't necessary for the on-disk representation. replication is
an optional field, and if we add another optional field for the EC policy, it won't be any
extra space.
> Also, we need to make sure to have the appropriate asserts in place to make sure both
fields aren't set for the same INodeField.



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