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https://issues.apache.org/jira/browse/HDFS-8900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14704529#comment-14704529
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Yi Liu commented on HDFS-8900:
------------------------------
This optimization:
- For each XAttr, can save: 12bytes (object overhead) + 2bytes (compact),
memory alignment of value
- For each XAttrFeature, can save: 12 bytes (object overhead) + num * XAttr
saved.
So for each XAttrFeature (associated with an INodeFile or INodeDirectory), we
can save (bytes): 12 + n * (14 + memory alignment of value in each XAttr)
The patch also makes code logic more simper, and has no impact on NN
performance.
Besides, the xattrMaxSize is used to restrict user/trust namespace xattrs, I
add a hard limit for max size. It's reasonable and make Xattr more
controllable.
> Optimize XAttr memory footprint.
> --------------------------------
>
> Key: HDFS-8900
> URL: https://issues.apache.org/jira/browse/HDFS-8900
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Yi Liu
> Assignee: Yi Liu
> Attachments: HDFS-8900.001.patch
>
>
> {code}
> private final ImmutableList<XAttr> xAttrs;
> {code}
> Currently we use above in XAttrFeature, it's not efficient from memory point
> of view, since {{ImmutableList}} and {{XAttr}} have object memory overhead,
> and each object has memory alignment.
> We can use a {{byte[]}} in XAttrFeature and do some compact in {{XAttr}}.
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