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https://issues.apache.org/jira/browse/HDFS-4489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13615677#comment-13615677
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Todd Lipcon commented on HDFS-4489:
-----------------------------------
bq. If you have an authoritative source, please send me that
Sure, from the JDK7 source code hotspot/src/share/vm/oops/arrayOop.hpp:
{code}
// The layout of array Oops is:
//
// markOop
// klassOop // 32 bits if compressed but declared 64 in LP64.
// length // shares klass memory or allocated after declared fields.
{code}
Important to note that the length of arrays is 32-bit, since array.length is an
int rather than a long. So given a 64-bit field for klassId, it can use 32-bits
for the actual class and 32 bits for the array length.
bq. I would like to run an experiment on a large production image. But I do not
have ready access to it and will have to spend time getting to it. Do you have
any?
Yes, I can run the experiment on a large image. Is HDFS-4434's patch ready to
apply so I can test it?
> Use InodeID as as an identifier of a file in HDFS protocols and APIs
> --------------------------------------------------------------------
>
> Key: HDFS-4489
> URL: https://issues.apache.org/jira/browse/HDFS-4489
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Reporter: Brandon Li
> Assignee: Brandon Li
>
> The benefit of using InodeID to uniquely identify a file can be multiple
> folds. Here are a few of them:
> 1. uniquely identify a file cross rename, related JIRAs include HDFS-4258,
> HDFS-4437.
> 2. modification checks in tools like distcp. Since a file could have been
> replaced or renamed to, the file name and size combination is no t reliable,
> but the combination of file id and size is unique.
> 3. id based protocol support (e.g., NFS)
> 4. to make the pluggable block placement policy use fileid instead of
> filename (HDFS-385).
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