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Date: Tue, 31 Jan 2017 18:59:52 +0000 (UTC)
From: "Andrew Wang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.13039264.1485889091000.1276.1485889192733@Atlassian.JIRA>
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Subject: [jira] (HDFS-11382) Persist Erasure Coding Policy ID in a new
 optional field in INodeFile in FSImage
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archived-at: Tue, 31 Jan 2017 19:00:03 -0000


     [ https://issues.apache.org/jira/browse/HDFS-11382?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrew Wang updated HDFS-11382:
-------------------------------
    Hadoop Flags: Incompatible change

> 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
>
> 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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