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From "Aaron Fabbri (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13761) S3Guard: implement retries for DDB failures and throttling; translate exceptions
Date Thu, 08 Feb 2018 02:19:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13761?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16356378#comment-16356378
] 

Aaron Fabbri commented on HADOOP-13761:
---------------------------------------

Thanks for the feedback on the scale test patch [~stevel@apache.org].  On the retries, I've
been looking at open(), delete(), and rename() in terms of what happens when MetadataStore
has metadata but we hit eventual consistency when we start operating on S3.

 
 * open(): This is the only code that creates a S3AInputStream constructor, and it does a
getFileStatus() first, so failures should be happening later in read() paths.  There is already
a single handler for read failures: {{onReadFailure()}}.  I suggest we add invoker/retry
policy to this function. Thoughts? As is, it appears to only retry once without any backoff
timer.
 * delete(): this uses deleteObject(), which already has retries. I think we are good here?
 * rename(): this is more complicated, and we probably need to do more in-depth rename() rewrite
to include HADOOP-15183.  One thing I noticed is, {{copyFile()}} is annotated {{RetryMixed}}
but only uses {{once()}} internally, so I might fix that.

I'd like to address Steve's feedback on the scale test and make the above changes if it sounds
good. I think rename() would benefit from its own patch/JIRA, (possibly even add a new experimental
"v2" rename codepath that can be switched in via config while we improve and test with it,
dunno).

> S3Guard: implement retries for DDB failures and throttling; translate exceptions
> --------------------------------------------------------------------------------
>
>                 Key: HADOOP-13761
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13761
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 3.0.0-beta1
>            Reporter: Aaron Fabbri
>            Assignee: Aaron Fabbri
>            Priority: Blocker
>         Attachments: HADOOP-13761.001.patch, HADOOP-13761.002.patch
>
>
> Following the S3AFileSystem integration patch in HADOOP-13651, we need to add retry logic.
> In HADOOP-13651, I added TODO comments in most of the places retry loops are needed,
including:
> - open(path).  If MetadataStore reflects recent create/move of file path, but we fail
to read it from S3, retry.
> - delete(path).  If deleteObject() on S3 fails, but MetadataStore shows the file exists,
retry.
> - rename(src,dest).  If source path is not visible in S3 yet, retry.
> - listFiles(). Skip for now. Not currently implemented in S3Guard. I will create a separate
JIRA for this as it will likely require interface changes (i.e. prefix or subtree scan).
> We may miss some cases initially and we should do failure injection testing to make sure
we're covered.  Failure injection tests can be a separate JIRA to make this easier to review.
> We also need basic configuration parameters around retry policy.  There should be a way
to specify maximum retry duration, as some applications would prefer to receive an error eventually,
than waiting indefinitely.  We should also be keeping statistics when inconsistency is detected
and we enter a retry loop.



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