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From "Gabor Bota (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15625) S3A input stream to use etags to detect changed source files
Date Tue, 12 Mar 2019 15:27:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15625?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16790651#comment-16790651
] 

Gabor Bota commented on HADOOP-15625:
-------------------------------------

My review on patch v15:

h3. S3AInputStream.java
 * Line 193 "open" and "re-open" could be constants instead of using string literals in the
code. It would be good still we started to use this string as a parameter in a function `changeTracker.processResponse()`

h3. S3ATestUtils.java
  There are two unused imports, please remove them:
*     56 import java.net.MalformedURLException;
*     59 import java.net.URL;

h3. troubleshooting_s3a.md
* Lines 718-729 and 735-747: you removed a tab from the start of those lines. What is the
reason for that?  

h3. ChangeDetectionPolicy.java
* Line 333: there's no @Override annotation before {{getSource}} method.

h3. TestStreamChangeTracker.java
* Lines 90, 166, 227: Nit: 'Tracker should not have applied contraints' typo: contraints ->
constraints

h3. index.md
 * The following could be emphasized more (like a warning):
{noformat}
1239 ...    this option should only be used when the S3 buckets
1240	have object versioning enabled from the beginning.
{noformat}

 * Nit in line 1261 {{s.s3a.change.detection.version.required}} should be {{fs.s3a.change.detection.version.required}}


> 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, HADOOP-15625-013.patch,
HADOOP-15625-014.patch, HADOOP-15625-015.patch, HADOOP-15625-015.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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