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From "Brahma Reddy Battula (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-15625) S3A input stream to use etags to detect changed source files
Date Fri, 03 Aug 2018 12:11:00 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Brahma Reddy Battula updated HADOOP-15625:
------------------------------------------
    Attachment: HADOOP-15625-002.patch

> 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
>
>
> 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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