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https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16778152#comment-16778152
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Steve Loughran commented on HADOOP-15625:
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FWIW, mandatory etag checking makes sense to me.
if something is overwriting files while you read them then it's good to know
next q: client-side or server side? if we do server, S3 is left with the
problem. Sole risk: third party stores? But if they ignore the x-modified
parameter, well, so what. It's only if one of (a) the header itself triggers a
failure
I think etag & server is probably the one to turn on (remember: AWS S3 is the
main endpoint we worry about). Others ([~ehiggs] get to test. But by adding an
incompatible change into the release notes, maybe something in the docs, then
people who see a problem can deal with it.
> 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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