[jira] [Commented] (SPARK-2288) Hide ShuffleBlockManager behind ShuffleManager

["Raymond Liu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-2288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045446#comment-14045446 ] 

Raymond Liu commented on SPARK-2288:
------------------------------------

Hi 

pull request at https://github.com/apache/spark/pull/1241

> Hide ShuffleBlockManager behind ShuffleManager
> ----------------------------------------------
>
>                 Key: SPARK-2288
>                 URL: https://issues.apache.org/jira/browse/SPARK-2288
>             Project: Spark
>          Issue Type: Sub-task
>          Components: Block Manager, Shuffle
>            Reporter: Raymond Liu
>
> This is a sub task for SPARK-2275. 
> At present, In shuffle write path, the shuffle block manager manage the mapping from some blockID to a FileSegment for the benefit of consolidate shuffle, this way it bypass the block store's blockId based access mode. Then in the read path, when read a shuffle block data, disk store query shuffleBlockManager to hack the normal blockId to file mapping in order to correctly read data from file. This really rend to a lot of bi-directional dependencies between modules and the code logic is some how messed up. None of the shuffle block manager and blockManager/Disk Store fully control the read path. They are tightly coupled in low level code modules. And it make it hard to implement other shuffle manager logics. e.g. a sort based shuffle which might merge all output from one map partition to a single file. This will need to hack more into the diskStore/diskBlockManager etc to find out the right data to be read.
> Possible approaching:
> So I think it might be better that we expose an FileSegment based read interface for DiskStore in addition to the current blockID based interface.
> Then those mapping blockId to FileSegment code logic can all reside in the specific shuffle manager, if they do need to merge data into one single object. they take care of the mapping logic in both read/write path and take the responsibility of read / write shuffle data
> The BlockStore itself should just take care of read/write as required, it should not involve into the data mapping logic at all. This might make the interface between modules more clear and decouple each other in a more clean way.



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