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https://issues.apache.org/jira/browse/HADOOP-12047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14979637#comment-14979637
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Kai Zheng commented on HADOOP-12047:
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Thanks Walter for the good review!
bq. Do I understand correctly?
Yeah, you understood very well. This issue is mainly to introduce
*ALLOW_CHANGE_INPUTS* option, but also adds *PREFER_DIRECT_BUFFER* option by
the way. The former is letting caller to set, and the later is fixed for a
coder, but letting caller to query. That's why CoderOption is not made
unmodifiable. Both options are used in other issues, like HDFS-8957 and etc.
for client and DN sides. I didn't use these new options here because using them
couples with other things and needs some clean up. Another option *ALLOW_DUMP*
is only used internally in a coder impl opened by tests and found useful while
developing the new Java coder and ISA-L coder.
bq. allowChangeInputs as a method name is like "do something" not "check
something"
Yeah, how about *IsChangeInputsAllowed*?
Will update the patch accordingly and also fixing the check style issues.
> Indicate preference not to affect input buffers during coding in erasure coder
> ------------------------------------------------------------------------------
>
> Key: HADOOP-12047
> URL: https://issues.apache.org/jira/browse/HADOOP-12047
> Project: Hadoop Common
> Issue Type: Sub-task
> Reporter: Kai Zheng
> Assignee: Kai Zheng
> Fix For: HDFS-7285
>
> Attachments: HADOOP-12047-HDFS-7285-v1.patch, HADOOP-12047-v2.patch,
> initial-poc.patch
>
>
> It's good to define and ensure input buffers are not affected during coding
> process in raw erasure coders. Below are copied from discussion with
> [~jingzhao] in HDFS-8481:
> bq. In that case we cannot reuse the source buffers I guess? Then do we need
> to expose this information in the decoder?
> bq. Good catch Jing! Yes in this case we can't reuse the source buffers here
> as they need to be passed to caller/applications without being changed. I'm
> planning to re-implement the Java coders in HADOOP-12041 and related, when
> done it's possible to ensure the input buffers not to be affected. Benefits
> of doing this in coder layer: 1) a more clear contract between coder and
> caller in more general sense for the inputs; 2) concrete coder may have
> specific tweak to optimize in the aspect, ideally no input data copying at
> all, worst, make the copy, but all transparent to callers; 3) allow new
> coders (LRC, HH) to be layered on other primitive coders (RS, XOR) more
> easily.
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