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https://issues.apache.org/jira/browse/HADOOP-2758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12569380#action_12569380
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Raghu Angadi commented on HADOOP-2758:
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Regd couple of concerns in Konstantin's review :
- > 2. Do we still need the notion of a chunk? [...]
-- I think so. A CRC chunk is still central to many things that DataNode and
DFSClients do. It is very useful for discussions, descriptions and even in code
to have a single word to consistently describe this essential unit of DFS data.
If we see a member called 'sendChunk()', its clear what it sends. For e.g. this
patch renamed {{sendChunk()}} to {{sendChunks(int)}} because it sends multiple
CRC chunks.
- > 5. DATA_TRANSFER_VERSION : I generally do not understand what is the
meaning of this constant, [...]
-- data transfers do not use RPCs. As noted in the comment, it unfortunately
does depend on Datanode serializations. Probably it should not. This is
analogous RPC versions and a Protocol version, which are at two different
levels of the stack.
> Reduce memory copies when data is read from DFS
> -----------------------------------------------
>
> Key: HADOOP-2758
> URL: https://issues.apache.org/jira/browse/HADOOP-2758
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Reporter: Raghu Angadi
> Assignee: Raghu Angadi
> Fix For: 0.17.0
>
> Attachments: HADOOP-2758.patch
>
>
> Currently datanode and client part of DFS perform multiple copies of data on
> the 'read path' (i.e. path from storage on datanode to user buffer on the
> client). This jira reduces these copies by enhancing data read protocol and
> implementation of read on both datanode and the client. I will describe the
> changes in next comment.
> Requirement is that this fix should reduce CPU used and should not cause
> regression in any benchmarks. It might not improve the benchmarks since most
> benchmarks are not cpu bound.
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