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https://issues.apache.org/jira/browse/HDFS-8901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15459053#comment-15459053
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Zhe Zhang commented on HDFS-8901:
---------------------------------
Thanks Sammi. I think all my previous comments have been addressed. But I see
some issues / questions in the changes from v17 to v18/19:
# Why do we need to flip? In the previous code, {{arraycopy}} just starts
copying from the current position of {{result}}.
{code}
- System.arraycopy(result.array(), result.position(), buf, offset,
- len);
+ result.flip();
{code}
# Could you also explain why {{TestPread}} and {{TestSnapshotFileLength}}
failed for v17 and v18 patches respectively?
# Need to be removed:
{code}
+ //buffer.position(buffer.position() + bytesToRead);
{code}
Thanks for adding the ByteBuffer version of readAll. Due to the size of the
current patch, can we create a separate JIRA just to add this API? It will go
through quickly and we can focus on the main logic on this JIRA.
Thanks for the great effort here.
> Use ByteBuffer in striping positional read
> ------------------------------------------
>
> Key: HDFS-8901
> URL: https://issues.apache.org/jira/browse/HDFS-8901
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Kai Zheng
> Assignee: SammiChen
> Attachments: HDFS-8901-v10.patch, HDFS-8901-v17.patch,
> HDFS-8901-v18.patch, HDFS-8901-v19.patch, HDFS-8901-v2.patch,
> HDFS-8901-v3.patch, HDFS-8901-v4.patch, HDFS-8901-v5.patch,
> HDFS-8901-v6.patch, HDFS-8901-v7.patch, HDFS-8901-v8.patch,
> HDFS-8901-v9.patch, HDFS-8901.v11.patch, HDFS-8901.v12.patch,
> HDFS-8901.v13.patch, HDFS-8901.v14.patch, HDFS-8901.v15.patch,
> HDFS-8901.v16.patch, initial-poc.patch
>
>
> Native erasure coder prefers to direct ByteBuffer for performance
> consideration. To prepare for it, this change uses ByteBuffer through the
> codes in implementing striping position read. It will also fix avoiding
> unnecessary data copying between striping read chunk buffers and decode input
> buffers.
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