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https://issues.apache.org/jira/browse/HDFS-13768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16627630#comment-16627630
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Arpit Agarwal commented on HDFS-13768:
--------------------------------------
bq. FsDatasetUtil.getGenrationStampFromFile(), This method loop over the all
the file to find out the meta file. This is time consuming. We can sort the
list of file's and in sorted list next to block file metafile will be there, so
we no need to loop and find out the meta file.
That's a nice find [~surendrasingh].
> Adding replicas to volume map makes DataNode start slowly
> -----------------------------------------------------------
>
> Key: HDFS-13768
> URL: https://issues.apache.org/jira/browse/HDFS-13768
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.1.0
> Reporter: Yiqun Lin
> Assignee: Surendra Singh Lilhore
> Priority: Major
> Attachments: HDFS-13768.01.patch, HDFS-13768.02.patch,
> HDFS-13768.03.patch, HDFS-13768.04.patch, HDFS-13768.patch, screenshot-1.png
>
>
> We find DN starting so slowly when rolling upgrade our cluster. When we
> restart DNs, the DNs start so slowly and not register to NN immediately. And
> this cause a lots of following error:
> {noformat}
> DataXceiver error processing WRITE_BLOCK operation src: /xx.xx.xx.xx:64360
> dst: /xx.xx.xx.xx:50010
> java.io.IOException: Not ready to serve the block pool,
> BP-1508644862-xx.xx.xx.xx-1493781183457.
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.checkAndWaitForBP(DataXceiver.java:1290)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.checkAccess(DataXceiver.java:1298)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:630)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:169)
> at
> org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:106)
> at
> org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:246)
> at java.lang.Thread.run(Thread.java:745)
> {noformat}
> Looking into the logic of DN startup, it will do the initial block pool
> operation before the registration. And during initializing block pool
> operation, we found the adding replicas to volume map is the most expensive
> operation. Related log:
> {noformat}
> 2018-07-26 10:46:23,771 INFO [Thread-105]
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Time to
> add replicas to map for block pool BP-1508644862-xx.xx.xx.xx-1493781183457 on
> volume /home/hard_disk/1/dfs/dn/current: 242722ms
> 2018-07-26 10:46:26,231 INFO [Thread-109]
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Time to
> add replicas to map for block pool BP-1508644862-xx.xx.xx.xx-1493781183457 on
> volume /home/hard_disk/5/dfs/dn/current: 245182ms
> 2018-07-26 10:46:32,146 INFO [Thread-112]
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Time to
> add replicas to map for block pool BP-1508644862-xx.xx.xx.xx-1493781183457 on
> volume /home/hard_disk/8/dfs/dn/current: 251097ms
> 2018-07-26 10:47:08,283 INFO [Thread-106]
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl: Time to
> add replicas to map for block pool BP-1508644862-xx.xx.xx.xx-1493781183457 on
> volume /home/hard_disk/2/dfs/dn/current: 287235ms
> {noformat}
> Currently DN uses independent thread to scan and add replica for each volume,
> but we still need to wait the slowest thread to finish its work. So the main
> problem here is that we could make the thread to run faster.
> The jstack we get when DN blocking in the adding replica:
> {noformat}
> "Thread-113" #419 daemon prio=5 os_prio=0 tid=0x00007f40879ff000 nid=0x145da
> runnable [0x00007f4043a38000]
> java.lang.Thread.State: RUNNABLE
> at java.io.UnixFileSystem.list(Native Method)
> at java.io.File.list(File.java:1122)
> at java.io.File.listFiles(File.java:1207)
> at org.apache.hadoop.fs.FileUtil.listFiles(FileUtil.java:1165)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:445)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:448)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addToReplicasMap(BlockPoolSlice.java:448)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.getVolumeMap(BlockPoolSlice.java:342)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.getVolumeMap(FsVolumeImpl.java:864)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeList$1.run(FsVolumeList.java:191)
> {noformat}
> One improvement maybe we can use ForkJoinPool to do this recursive task,
> rather than a sync way. This will be a great improvement because it can
> greatly speed up recovery process.
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