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https://issues.apache.org/jira/browse/HBASE-20431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16450053#comment-16450053
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Steve Loughran commented on HBASE-20431:
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* you are correct, neither PUT or multipart upload "MPU" has any visible
outcome until they are complete. MPUs can be completed in a POST from a
different host than that/those uploading blocks, which is how we implement the
S3A committers. Talk to [~ehiggs] & [~Thomas Demoor] about theirideas for
making that public. If you could use a single MPU to commit the final output,
you get a nice O(1) atomic operation.
* PUT-COPY is atomic, but it's a 6-10MB/s atomic operation; it's essentially
what you get when you rename() a single file. though there we DELETE the source
afterwards. We could expose it for S3 & the other stores which offer a similar
operation. One thought to consider: although its O(data), its bandwidth is ~0,
so you can do most of the copies in parallel.
* You aren't worrying about S3 consistency here. For AWS S3 life is easier if
you mandate using S3Guard for the consistency layer. Otherwise, you can turn on
fault injection in the S3A connector and see what breaks...
Looking forward to see what you do here, offering some consultancy on design
and test strategies, carefully not volunteering to provide any code...
> Store commit transaction for filesystems that do not support an atomic rename
> -----------------------------------------------------------------------------
>
> Key: HBASE-20431
> URL: https://issues.apache.org/jira/browse/HBASE-20431
> Project: HBase
> Issue Type: Sub-task
> Reporter: Andrew Purtell
> Priority: Major
>
> HBase expects the Hadoop filesystem implementation to support an atomic
> rename() operation. HDFS does. The S3 backed filesystems do not. The
> fundamental issue is the non-atomic and eventually consistent nature of the
> S3 service. A S3 bucket is not a filesystem. S3 is not always immediately
> read-your-writes. Object metadata can be temporarily inconsistent just after
> new objects are stored. There can be a settling period to ride over.
> Renaming/moving objects from one path to another are copy operations with
> O(file) complexity and O(data) time followed by a series of deletes with
> O(file) complexity. Failures at any point prior to completion will leave the
> operation in an inconsistent state. The missing atomic rename semantic opens
> opportunities for corruption and data loss, which may or may not be
> repairable with HBCK.
> Handling this at the HBase level could be done with a new multi-step
> filesystem transaction framework. Call it StoreCommitTransaction.
> SplitTransaction and MergeTransaction are well established cases where even
> on HDFS we have non-atomic filesystem changes and are our implementation
> template for the new work. In this new StoreCommitTransaction we'd be moving
> flush and compaction temporaries out of the temporary directory into the
> region store directory. On HDFS the implementation would be easy. We can rely
> on the filesystem's atomic rename semantics. On S3 it would be work: First we
> would build the list of objects to move, then copy each object into the
> destination, and then finally delete all objects at the original path. We
> must handle transient errors with retry strategies appropriate for the action
> at hand. We must handle serious or permanent errors where the RS doesn't need
> to be aborted with a rollback that cleans it all up. Finally, we must handle
> permanent errors where the RS must be aborted with a rollback during region
> open/recovery. Note that after all objects have been copied and we are
> deleting obsolete source objects we must roll forward, not back. To support
> recovery after an abort we must utilize the WAL to track transaction
> progress. Put markers in for StoreCommitTransaction start and completion
> state, with details of the store file(s) involved, so it can be rolled back
> during region recovery at open. This will be significant work in HFile,
> HStore, flusher, compactor, and HRegion. Wherever we use HDFS's rename now we
> would substitute the running of this new multi-step filesystem transaction.
> We need to determine this for certain, but I believe on S3 the PUT or
> multipart upload of an object must complete before the object is visible, so
> we don't have to worry about the case where an object is visible before fully
> uploaded as part of normal operations. So an individual object copy will
> either happen entirely and the target will then become visible, or it won't
> and the target won't exist.
> S3 has an optimization, PUT COPY
> (https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectCOPY.html), which
> the AmazonClient embedded in S3A utilizes for moves. When designing the
> StoreCommitTransaction be sure to allow for filesystem implementations that
> leverage a server side copy operation. Doing a get-then-put should be
> optional. (Not sure Hadoop has an interface that advertises this capability
> yet; we can add one if not.)
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