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https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16783884#comment-16783884
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Steve Loughran commented on HADOOP-15625:
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* s3a doesn't work with snowball at all, I do know of some interest in distcp
to it working, with the result then being fedexed to the final Se3 store. The
support needed will be minimal
A key thing: we have to plan for some endpoints not having etags. And if
someone went from unversioned to versioned, the may be unversioned files in the
store
* S3Select. Good point. For the s3guard integration, maybe the strategy will
be: do a HEAD until either the etag matches or a stability threshold has been
reached, but not worry about changes during a read. Be interesting to
experiment to see what happens...you could probably infer something from that
behaviour. (e.g some cursor on the read for the paged lists, every time you ask
for a new page it scans some more.
Not had a chance to look @ your patch yet, will do it tomorrow.
> 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, HADOOP-15625-007.patch,
> HADOOP-15625-008.patch, HADOOP-15625-009.patch, HADOOP-15625-010.patch,
> HADOOP-15625-011.patch, HADOOP-15625-012.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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