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https://issues.apache.org/jira/browse/HADOOP-14520?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16134151#comment-16134151
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Steve Loughran commented on HADOOP-14520:
-----------------------------------------

I've been looking at the current page blob code, and I've seen something else I 
think may need fixing; how things close

* {{PageBlobOutputStream.close()}} call is completely {{synchronized}}, even 
during a long upload. Which means that until that upload completes, all calls 
may block
* I don't see the flush or wrtie calls checking for the stream being open 
before doing anything, meaning that the only way that the state will be checked 
is internally, in  {{iopool.execute()}} or elsewhere.

I think here it'd be good to move to an atomic boolean to manage closed state, 
and use it as the guard to the operations.



> WASB: Block compaction for Azure Block Blobs
> --------------------------------------------
>
>                 Key: HADOOP-14520
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14520
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs/azure
>    Affects Versions: 3.0.0-alpha3
>            Reporter: Georgi Chalakov
>            Assignee: Georgi Chalakov
>         Attachments: HADOOP-14520-006.patch, HADOOP-14520-05.patch
>
>
> Block Compaction for WASB allows uploading new blocks for every hflush/hsync 
> call. When the number of blocks is above 32000, next hflush/hsync triggers 
> the block compaction process. Block compaction replaces a sequence of blocks 
> with one block. From all the sequences with total length less than 4M, 
> compaction chooses the longest one. It is a greedy algorithm that preserve 
> all potential candidates for the next round. Block Compaction for WASB 
> increases data durability and allows using block blobs instead of page blobs. 
> By default, block compaction is disabled. Similar to the configuration for 
> page blobs, the client needs to specify HDFS folders where block compaction 
> over block blobs is enabled. 
> Results for HADOOP-14520-05.patch
> tested endpoint: fs.azure.account.key.hdfs4.blob.core.windows.net
> Tests run: 707, Failures: 0, Errors: 0, Skipped: 119



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