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https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16777445#comment-16777445
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Steve Loughran commented on HADOOP-15625:
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Ben: I've done an interation on this; handing back to you. The key change is
(apart from moving the classes into a new package), pulling the change logic
out of S3AInputStream and into a self contained change tracker class, whose
logic we can test in a unit test.
Testing: unit tests done, did a test of the input stream but not rerun it since
my last set of changes. It's late. Sorry.
Handing it back to you for some of the todo list, especially: should we have an
option to require version checking?
Other than that
* Style checking. Javadocs are critical as java 8 needs the "." at the end.
Line length-wise, we like to keep down to nearly 80, due to the goal of
side-by-side diff checking. I know, it'd be good to move on a some point, but
until then...
* Docs. Something to discuss the option.
* core-site.xml: Add the default options there (etag @ warn?) alongside the
other fs.s3a options.
I've pushed up to github a branch which first applied your patch 005, then
added the new code. If you cherry pick the head of that branch, your local
branch will catch up
https://github.com/steveloughran/hadoop/tree/s3/HADOOP-15625-streamchanged
> S3A input stream to use etags to detect changed source files
> ------------------------------------------------------------
>
> Key: HADOOP-15625
> URL: https://issues.apache.org/jira/browse/HADOOP-15625
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.2.0
> Reporter: Brahma Reddy Battula
> Assignee: Brahma Reddy Battula
> Priority: Major
> Attachments: HADOOP--15625-006.patch, HADOOP-15625-001.patch,
> HADOOP-15625-002.patch, HADOOP-15625-003.patch, HADOOP-15625-004.patch,
> HADOOP-15625-005.patch, HADOOP-15625-006.patch
>
>
> S3A input stream doesn't handle changing source files any better than the
> other cloud store connectors. Specifically: it doesn't noticed it has
> changed, caches the length from startup, and whenever a seek triggers a new
> GET, you may get one of: old data, new data, and even perhaps go from new
> data to old data due to eventual consistency.
> We can't do anything to stop this, but we could detect changes by
> # caching the etag of the first HEAD/GET (we don't get that HEAD on open with
> S3Guard, BTW)
> # on future GET requests, verify the etag of the response
> # raise an IOE if the remote file changed during the read.
> It's a more dramatic failure, but it stops changes silently corrupting things.
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