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https://issues.apache.org/jira/browse/HDFS-8900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14705813#comment-14705813
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Andrew Wang commented on HDFS-8900:
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I talked with [~cmccabe] about compatibility offline, we had a few thoughts:
* Unlimited size xattrs are an anti-pattern and not that useful. Same for very
large xattrs in general.
* For branch-2, one compatible approach is to size the length field based on
the max size config, up to a full 4-byte signed integer. This is what
"unlimited" currently means anyway. Then, do a trunk follow-on to just use a
2-byte length and maybe get rid of the max size config in favor of the hard
limit.
* Practically speaking, it's unlikely anyone's ever changed the max size, so
the impact of the incompatibility is limited. Patch might be fine for branch-2
as is.
> 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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