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https://issues.apache.org/jira/browse/HADOOP-12047?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14980235#comment-14980235
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Walter Su commented on HADOOP-12047:
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Thanks [~drankye] for the explanation! It sounds reasonable to me.
1. The amount of temporary buf allocated is the same as inputs. Create many
on-heap ByteBuffer affects GC. Create many off-heap ByteBuffer is slow. We
should cache the temporary bytebuffer, also the temporary array.
2. Instead of {{inputs\[i\].mark();}} then {{reset()}}, we can use
{{duplicate()}} or {{slice()}} to avoid change the inputs' position.
> 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,
> HADOOP-12047-v3.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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