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https://issues.apache.org/jira/browse/HDFS-6803?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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stack updated HDFS-6803:
------------------------
Attachment: DocumentingDFSClientDFSInputStream.v2.pdf
Need license to improve pread so back here again (pardon the absence).
Attach v2 of the doc addressing nice feedback. Dropped assertion 2.3 on
filelength after [~cmccabe]'s feedback above ("too much" and "too little") so
now we are just assertions "2.1. Positional read and non-positional read can
run concurrently" and "2.2. Two or more positional reads can run concurrently"
On adding a ConcurrentPositionalReads marker Interface, I'd say its probably
too late for this now; we've assumed we could do concurrent positional reads
always and it sort of works (slowly). Would it be better marking those fs that
do NOT support ConcurrentPositionalReads? (Probably not -- too much work).
bq. I think stack's point 2.1 and 2.2 imply that pread can safely be called
from multiple threads concurrently. I guess we should document this too so that
there's no confusion.
This is in the attached doc. Will forward port it.
> 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: 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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