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Posted to common-issues@hadoop.apache.org by "Steve Loughran (JIRA)" <ji...@apache.org> on 2019/01/14 19:51:00 UTC
[jira] [Commented] (HADOOP-15625) S3A input stream to use etags to
detect changed source files
[ https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16742453#comment-16742453 ]
Steve Loughran commented on HADOOP-15625:
-----------------------------------------
Not forgotten this....HADOOP-15229 helps set things up for passing in the checksum in the open operation, when known. And we need to implement retries in HADOOP-15894
> 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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