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https://issues.apache.org/jira/browse/HDFS-492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12739258#action_12739258
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Bill Zeller commented on HDFS-492:
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The second argument is the startingBlockId, not the starting block offset.
Passing 0 indicates a block id of 0. This function could be special cased to
treat 0 to mean to start from the beginning and assume that no real block id
would ever have the value 0, but this seems to be dirtier than just using
{{null}}.
> Expose corrupt replica/block information
> ----------------------------------------
>
> 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
> Assignee: Bill Zeller
> Priority: Minor
> Fix For: 0.21.0
>
> Attachments: hdfs-492-4.patch, hdfs-492-5.patch
>
> Original Estimate: 48h
> Remaining Estimate: 48h
>
> 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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