[jira] Created: (HDFS-492) Expose corrupt replica/block information

["Bill Zeller (JIRA)" <ji...@apache.org>]

Expose corrupt replica/block information
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                 Key: HDFS-492
                 URL: https://issues.apache.org/jira/browse/HDFS-492
             Project: Hadoop HDFS
          Issue Type: New Feature
          Components: data-node, name-node
    Affects Versions: 0.21.0
            Reporter: Bill Zeller
            Priority: Minor


This adds two additional functions to FSNamesystem to provide more information about corrupt replicas. It also adds two servlets to the namenode that provide information (in JSON) about all blocks with corrupt replicas as well as information about a specific block. It also changes the file browsing servlet by adding a link from block ids to the above mentioned block information page.

These JSON pages are designed to be used by client side tools which wish to analyze corrupt block/replicas. The only change to an existing (non-servlet) class is described below).  

Currently, CorruptReplicasMap stores a map of corrupt replica information and allows insertion and deletion. It also gives information about the corrupt replicas for a specific block. It does not allow iteration over all corrupt blocks. Two additional functions will be added to FSNamesystem (which will call BlockManager which will call CorruptReplicasMap). The first will return the size of the corrupt replicas map, which represents the number of blocks that have corrupt replicas (but less than the number of corrupt replicas if a block has multiple corrupt replicas). The second will allow "paging" through a list of block ids that contain corrupt replicas:

{{  public synchronized List<Long> getCorruptReplicaBlockIds(int n, Long startingBlockId) }}

{{n}} is the number of block ids to return and {{startingBlockId}} is the block id offset. To prevent a large number of items being returned at one time, n is constrained to 0 <= {{n}} <= 100. If {{startingBlockId}} is null, up to {{n}} items are returned starting at the beginning of the list. Ordering is enforced through the internal use of TreeMap in CorruptReplicasMap.

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