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https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16566024#comment-16566024
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Steve Loughran commented on HADOOP-15625:
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-1
you have getObjectMetadata() in open(), so added another HTTP round trip; extra
on top of the already slow open sequence without S3Guard, and an HTTP request
where one doesn't exist with S3Guard
# in S3AInputStream.reopen(), the first GET should return that etag
# which can be stored in the S3AInputStream field
# After that, subsequent reopens can validate the etag returned, or include
that tag in an unless-modified header in the call. (BTW, some issues related to
etag checking [may exist in the
SDK|https://github.com/aws/aws-sdk-java/issues/1211].
This won't pick up a change in the source file between open() returning and the
first read/readfully, but it will ensure that later changes will fail fast
bq. Ran the tests after this changes,there were failures related to this ( seen
some encryption errors).
# make sure you've got all the s3 tests running before trying to change things,
and that includes the s3guard stuff
# state which specific S3 endpoint you've been playing with
# if there were failures, list the tests which failed, as it could be new
stuff. For example, encryption & etags may be a source of surprises (I don't
think it will, but still..)
> 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
> Priority: Major
> Attachments: HADOOP-15625-001.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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