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https://issues.apache.org/jira/browse/HDFS-12737?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16243215#comment-16243215
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Yongjun Zhang commented on HDFS-12737:
--------------------------------------
Thanks a lot [~jnp] and [~tlipcon]!
I did some study and figure out this: Connection is associated with a Socket,
which allows only one input stream and one output stream, if we really want to
share the same Connection to a DN for multiple blocks, we need to handle
multiplexing, which we don't do.
So I think we can conclude that the current design is, one Connection can only
be used for one block at the same time.
If we are to implement multiplexing in the future, can either take Todd's
suggestion of passing tokens as parameter, or modify Token Selector to select
not only token type, but also block id for BlockToken.
Thanks.
> Thousands of sockets lingering in TIME_WAIT state due to frequent file open
> operations
> --------------------------------------------------------------------------------------
>
> Key: HDFS-12737
> URL: https://issues.apache.org/jira/browse/HDFS-12737
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: ipc
> Environment: CDH5.10.2, HBase Multi-WAL=2, 250 replication peers
> Reporter: Wei-Chiu Chuang
> Assignee: Wei-Chiu Chuang
>
> On a HBase cluster we found HBase RegionServers have thousands of sockets in
> TIME_WAIT state. It depleted system resources and caused other services to
> fail.
> After months of troubleshooting, we found the issue is the cluster has
> hundreds of replication peers, and has multi-WAL = 2. That creates hundreds
> of replication threads in HBase RS, and each thread opens WAL file *every
> second*.
> We found that the IPC client closes socket right away, and does not reuse
> socket connection. Since each closed socket stays in TIME_WAIT state for 60
> seconds in Linux by default, that generates thousands of TIME_WAIT sockets.
> {code:title=ClientDatanodeProtocolTranslatorPB:createClientDatanodeProtocolProxy}
> // Since we're creating a new UserGroupInformation here, we know that no
> // future RPC proxies will be able to re-use the same connection. And
> // usages of this proxy tend to be one-off calls.
> //
> // This is a temporary fix: callers should really achieve this by using
> // RPC.stopProxy() on the resulting object, but this is currently not
> // working in trunk. See the discussion on HDFS-1965.
> Configuration confWithNoIpcIdle = new Configuration(conf);
> confWithNoIpcIdle.setInt(CommonConfigurationKeysPublic
> .IPC_CLIENT_CONNECTION_MAXIDLETIME_KEY, 0);
> {code}
> This piece of code is used in DistributedFileSystem#open()
> {noformat}
> 2017-10-27 14:01:44,152 DEBUG org.apache.hadoop.ipc.Client: New connection
> Thread[IPC Client (1838187805) connection to /172.131.21.48:20001 from
> blk_1013754707_14032,5,main] for remoteId /172.131.21.48:20001
> java.lang.Throwable: For logging stack trace, not a real exception
> at org.apache.hadoop.ipc.Client.getConnection(Client.java:1556)
> at org.apache.hadoop.ipc.Client.call(Client.java:1482)
> at org.apache.hadoop.ipc.Client.call(Client.java:1443)
> at
> org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:230)
> at com.sun.proxy.$Proxy28.getReplicaVisibleLength(Unknown Source)
> at
> org.apache.hadoop.hdfs.protocolPB.ClientDatanodeProtocolTranslatorPB.getReplicaVisibleLength(ClientDatanodeProtocolTranslatorPB.java:198)
> at
> org.apache.hadoop.hdfs.DFSInputStream.readBlockLength(DFSInputStream.java:365)
> at
> org.apache.hadoop.hdfs.DFSInputStream.fetchLocatedBlocksAndGetLastBlockLength(DFSInputStream.java:335)
> at
> org.apache.hadoop.hdfs.DFSInputStream.openInfo(DFSInputStream.java:271)
> at
> org.apache.hadoop.hdfs.DFSInputStream.<init>(DFSInputStream.java:263)
> at org.apache.hadoop.hdfs.DFSClient.open(DFSClient.java:1585)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:326)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:322)
> at
> org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem.open(DistributedFileSystem.java:322)
> at
> org.apache.hadoop.fs.FilterFileSystem.open(FilterFileSystem.java:162)
> at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:783)
> at
> org.apache.hadoop.hbase.wal.WALFactory.createReader(WALFactory.java:293)
> at
> org.apache.hadoop.hbase.wal.WALFactory.createReader(WALFactory.java:267)
> at
> org.apache.hadoop.hbase.wal.WALFactory.createReader(WALFactory.java:255)
> at
> org.apache.hadoop.hbase.wal.WALFactory.createReader(WALFactory.java:414)
> at
> org.apache.hadoop.hbase.replication.regionserver.ReplicationWALReaderManager.openReader(ReplicationWALReaderManager.java:70)
> at
> org.apache.hadoop.hbase.replication.regionserver.ReplicationSource$ReplicationSourceWorkerThread.openReader(ReplicationSource.java:747)
> at
> org.apache.hadoop.hbase.replication.regionserver.ReplicationSource$ReplicationSourceWorkerThread.run(ReplicationSource.java:543)
> {noformat}
> Unfortunately, given the HBase's usage pattern, this hack creates the problem.
> Ignoring the fact that having hundreds of HBase replication peers is a bad
> practice (I'll probably file a HBASE jira to help remedy that), the fact that
> Hadoop IPC client does not reuse socket seems not right. The relevant code is
> historical and deep in the stack, so I'd like to invite comments. I have a
> patch but it's pretty hacky.
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