[jira] [Commented] (HDFS-4885) Update verifyBlockPlacement() API in BlockPlacementPolicy

["Luke Lu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-4885?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13782099#comment-13782099 ] 

Luke Lu commented on HDFS-4885:
-------------------------------

I think this API change is problematic for several reasons:

# Loss of useful information by replacing the rack diff with a boolean. We should preserve existing information as much as possible if we're generalizing the API.
# Not general enough. minRacks is not general enough for a generic API. 
# srcPath is useful for info/debug status.

Suggestion:
{code}
public BlockPlacementStatus verifyBlockPlacement(String srcPath, LocatedBlock blk, BlockPlacementConstraints constraints);
{code}

Since override is covariant on return type (since java 5), new BlockPlacementStatus can be implemented for new BlockPlacementPolicy later on without any information loss.

> Update verifyBlockPlacement() API in BlockPlacementPolicy
> ---------------------------------------------------------
>
>                 Key: HDFS-4885
>                 URL: https://issues.apache.org/jira/browse/HDFS-4885
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Junping Du
>            Assignee: Junping Du
>              Labels: BlockPlacementPolicy
>         Attachments: HDFS-4885.patch
>
>
> verifyBlockPlacement() has unused parameter -srcPath as its responsibility just verify single block rather than files under a specific path. Also the return value (int) does not make sense as the violation of block placement has other case than number of racks, so boolean value should be better.



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