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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15625) S3A input stream to use etags to detect changed source files
Date Tue, 05 Mar 2019 23:36:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16785037#comment-16785037
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Steve Loughran commented on HADOOP-15625:
-----------------------------------------

I patch 012, I Think we're pretty much done. Here are my comments, which I've done in my IDE
and attached as a diff to be applied to the 012 patch, and as a -013 patch for yetus to play
with. 

I like this, Set up a bucket with versioning on, reran the tests. I think I'll need to do
that for a while to see that I'm happy with it (+ with etag checking on by default, that happens
on every
bucket)

* nice to see the change in S3ARetryPolicy. It would have failed anyway, but it is good to
see the explicit decision.

h2. Constants

rename "fs.s3a.change.detection.versionrequired" to "fs.s3a.change.detection.version.required"
here,
core-site.xml.


h3. S3AInstrumentation

L646. Make versionMismatches private (checkstyle, inevitably my fault)


h3. S3AFileSystem

mark getChangeDetectionPolicy as {{@VisibleForTesting}}

h3. index.md

- some typos, `` markup and text changes.

h3. troubleshooting_s3a.md

-add `` round code
-a typo
-add `` round code
-cut down wide lines
in the stack traces and convert tabs to spaces there too.

h3. ITestS3ARemoteFileChanged

unset the bucket options in case someone has set a per-bucket override. Added a method to
S3ATestUtils here.


> 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, HADOOP-15625-013-delta.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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