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https://issues.apache.org/jira/browse/HDFS-13671?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16510658#comment-16510658
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Yiqun Lin commented on HDFS-13671:
----------------------------------

Hi [~xiaochen], the deletion behavior is invoked by trash mechanism. So this 
will happened very frequently in our cluster, Every time there are 12~14w 
files(blocks) being deleted, then we found NN hung around 3~5 minutes. And all 
the other RPC requests are blocked.

> Namenode deletes large dir slowly caused by FoldedTreeSet#removeAndGet
> ----------------------------------------------------------------------
>
>                 Key: HDFS-13671
>                 URL: https://issues.apache.org/jira/browse/HDFS-13671
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 3.1.0, 3.0.3
>            Reporter: Yiqun Lin
>            Priority: Major
>
> NameNode hung when deleting large files/blocks. The stack info:
> {code}
> "IPC Server handler 4 on 8020" #87 daemon prio=5 os_prio=0 
> tid=0x00007fb505b27800 nid=0x94c3 runnable [0x00007fa861361000]
>    java.lang.Thread.State: RUNNABLE
>       at 
> org.apache.hadoop.hdfs.util.FoldedTreeSet.compare(FoldedTreeSet.java:474)
>       at 
> org.apache.hadoop.hdfs.util.FoldedTreeSet.removeAndGet(FoldedTreeSet.java:849)
>       at 
> org.apache.hadoop.hdfs.util.FoldedTreeSet.remove(FoldedTreeSet.java:911)
>       at 
> org.apache.hadoop.hdfs.server.blockmanagement.DatanodeStorageInfo.removeBlock(DatanodeStorageInfo.java:252)
>       at 
> org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.removeBlock(BlocksMap.java:194)
>       at 
> org.apache.hadoop.hdfs.server.blockmanagement.BlocksMap.removeBlock(BlocksMap.java:108)
>       at 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.removeBlockFromMap(BlockManager.java:3813)
>       at 
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.removeBlock(BlockManager.java:3617)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.removeBlocks(FSNamesystem.java:4270)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.deleteInternal(FSNamesystem.java:4244)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.deleteInt(FSNamesystem.java:4180)
>       at 
> org.apache.hadoop.hdfs.server.namenode.FSNamesystem.delete(FSNamesystem.java:4164)
>       at 
> org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.delete(NameNodeRpcServer.java:871)
>       at 
> org.apache.hadoop.hdfs.server.namenode.AuthorizationProviderProxyClientProtocol.delete(AuthorizationProviderProxyClientProtocol.java:311)
>       at 
> org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.delete(ClientNamenodeProtocolServerSideTranslatorPB.java:625)
>       at 
> org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
>       at 
> org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:617)
> {code}
> In the current deletion logic in NameNode, there are mainly two steps:
> * Collect INodes and all blocks to be deleted, then delete INodes.
> * Remove blocks  chunk by chunk in a loop.
> Actually the first step should be a more expensive operation and will takes 
> more time. However, now we always see NN hangs during the remove block 
> operation. 
> Looking into this, we introduced a new structure {{FoldedTreeSet}} to have a 
> better performance in dealing FBR/IBRs. But compared with early 
> implementation in remove-block logic, {{FoldedTreeSet}} seems more slower 
> since It will take additional time to balance tree node. When there are large 
> block to be removed/deleted, it looks bad.
> For the get type operations in {{DatanodeStorageInfo}}, we only provide the 
> {{getBlockIterator}} to return blocks iterator and no other get operation 
> with specified block. Still we need to use {{FoldedTreeSet}} in 
> {{DatanodeStorageInfo}}? As we know {{FoldedTreeSet}} is benefit for Get not 
> Update. Maybe we can revert this to the early implementation.



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