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https://issues.apache.org/jira/browse/HDFS-6803?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14195980#comment-14195980
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Steve Loughran commented on HDFS-6803:
--------------------------------------
maybe we should say
MUST be consistent with serialized operations
SHOULD be concurrent
What we really wants is for two parallel operations to always produce the right
data; concurrency boosts throughput, but is not guarantees
{code}
read(pos1,dest,, len) ->
dest[0..len-1] = [data(FS, path, pos1), data(FS, path, pos1+1) ... data(FS,
path, pos1+ len -1]
{code}
and {{read(pos2, dest2, len2)}} does the same for pos2..pos2+len2-1
This defines the isolation; the SHOULD/MAY sets the policy.
> Documenting DFSClient#DFSInputStream expectations reading and preading in
> concurrent context
> --------------------------------------------------------------------------------------------
>
> Key: HDFS-6803
> URL: https://issues.apache.org/jira/browse/HDFS-6803
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: hdfs-client
> Affects Versions: 2.4.1
> Reporter: stack
> Attachments: 9117.md.txt, DocumentingDFSClientDFSInputStream (1).pdf,
> DocumentingDFSClientDFSInputStream.v2.pdf
>
>
> Reviews of the patch posted the parent task suggest that we be more explicit
> about how DFSIS is expected to behave when being read by contending threads.
> It is also suggested that presumptions made internally be made explicit
> documenting expectations.
> Before we put up a patch we've made a document of assertions we'd like to
> make into tenets of DFSInputSteam. If agreement, we'll attach to this issue
> a patch that weaves the assumptions into DFSIS as javadoc and class comments.
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