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https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16765485#comment-16765485
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Ben Roling commented on HADOOP-15625:
-------------------------------------
I've got a patch that modifies only S3AInputStream and adds no new remote
calls. Additionally, it modifies the
ITestS3AFailureHandling.testReadFileChanged() test case, which was already
testing the concurrent read and write scenario. Previously the test had the
expectation of EOF on a read after a seek backwards past the new length of the
file with a concurrent write of a smaller file. In my patch the test expects
an IOException after any seek backwards.
> 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-15625-001.patch, HADOOP-15625-002.patch,
> HADOOP-15625-003.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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