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https://issues.apache.org/jira/browse/HADOOP-2576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12561866#action_12561866
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Raghu Angadi commented on HADOOP-2576:
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Another issue that contributes this problem and made worse by large heartbeat :
# For each heartbeat, Namenode asks a datanode to delete blocks only the
datanode does not need to transfer (for replication, rebalancing etc) any
blocks. I don't see any reason by datanode can not do both. If a datanode gets
asked to transfer one block in each minute, it never deletes anything.
# Similarly 'computeDatanodeWork()' does the same: it moves blocks from
recentInvalidates to datanode's list only if no transfers are scheduled on a
node.
> Namenode performance degradation over time
> ------------------------------------------
>
> Key: HADOOP-2576
> URL: https://issues.apache.org/jira/browse/HADOOP-2576
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.16.0
> Reporter: Christian Kunz
> Assignee: Raghu Angadi
> Priority: Blocker
> Fix For: 0.16.0
>
> Attachments: HADOOP-2576.patch
>
>
> We have a cluster running the same applications again and again with a high
> turnover of files.
> The performance of these applications seem to be correlated to the lifetime
> of the namenode:
> After starting the namenode, the applications need increasingly more time to
> complete, with about 50% more time after 1 week.
> During that time the namenode average cpu usage increases from typically 10%
> to 30%, memory usage nearly doubles (although the average amount of data on
> dfs stays the same), and the average load factor increases by a factor of 2-3
> (although not significantly high, <2).
> When looking at the namenode and datanode logs, I see a lot of asks to delete
> blocks coming from the namenode for blocks not in the blockmap of the
> datanodes, repeatedly for the same blocks.
> When I counted the number of blocks asked by the namenode to be deleted, I
> noticed a noticeable increase with the lifetime of the namenode (a factor of
> 2-3 after 1 week).
> This makes me wonder whether the namenode does not purge the list of invalid
> blocks from non-existing blocks.
> But independently, the namenode has a degradation issue.
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