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https://issues.apache.org/jira/browse/HADOOP-13786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15937088#comment-15937088
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Steve Loughran commented on HADOOP-13786:
-----------------------------------------

Its not so much the code quantity as the fact you end up with having to know 
the commit protocol before you can judge the quality of it, and that's 
something else to learn. I learned it by single-stepping through the debugger.

I think I could/should split out the magic committer as it is the one doing 
more to the internals of s3aFS. I think it's a good evolutionary feature, but 
the staging one should ship first. In which case some of the S3aFS logic can be 
temporarily culled, though I'd like to retain the changes to the block output 
stream to allow it to write-complete vs write-pending. the enhancements to 
WriteOperationsHelper, json persistent format &c are actually things the 
staging committer(s) can share -and will be needed to keep s3guard's DDB tables 
up to speed.

I could to a tour early next week, say tuesday morning PST?

> Add S3Guard committer for zero-rename commits to consistent S3 endpoints
> ------------------------------------------------------------------------
>
>                 Key: HADOOP-13786
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13786
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: fs/s3
>    Affects Versions: HADOOP-13345
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: HADOOP-13786-HADOOP-13345-001.patch, 
> HADOOP-13786-HADOOP-13345-002.patch, HADOOP-13786-HADOOP-13345-003.patch, 
> HADOOP-13786-HADOOP-13345-004.patch, HADOOP-13786-HADOOP-13345-005.patch, 
> HADOOP-13786-HADOOP-13345-006.patch, HADOOP-13786-HADOOP-13345-006.patch, 
> HADOOP-13786-HADOOP-13345-007.patch, HADOOP-13786-HADOOP-13345-009.patch, 
> HADOOP-13786-HADOOP-13345-010.patch, HADOOP-13786-HADOOP-13345-011.patch, 
> HADOOP-13786-HADOOP-13345-012.patch, HADOOP-13786-HADOOP-13345-013.patch, 
> HADOOP-13786-HADOOP-13345-015.patch, HADOOP-13786-HADOOP-13345-016.patch, 
> HADOOP-13786-HADOOP-13345-017.patch, HADOOP-13786-HADOOP-13345-018.patch, 
> s3committer-master.zip
>
>
> A goal of this code is "support O(1) commits to S3 repositories in the 
> presence of failures". Implement it, including whatever is needed to 
> demonstrate the correctness of the algorithm. (that is, assuming that s3guard 
> provides a consistent view of the presence/absence of blobs, show that we can 
> commit directly).
> I consider ourselves free to expose the blobstore-ness of the s3 output 
> streams (ie. not visible until the close()), if we need to use that to allow 
> us to abort commit operations.



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