[HDFS-13768] Adding replicas to volume map makes DataNode start slowly

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.1.0
• Fix Version/s: 2.10.0, 3.2.0, 3.1.2
• Target Version/s: 2.10.0, 3.2.0, 3.1.2
• Hadoop Flags: Reviewed
• Assignee: Surendra Singh Lilhore
• Reporter: Yiqun Lin
• Created: 26/Jul/18 05:38
• Updated: 01/Feb/19 13:09
• Resolved: 09/Oct/18 02:21

Description

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:

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)

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:

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

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:

"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)

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.

Issue Links

• causes: HDFS-14251 BlockPoolSlice ForkJoinPool introduced by HDFS-13768 breaks under Java SecurityManager
• is related to: HDFS-13962 Add null check for add-replica pool to avoid lock acquiring
• is related to: SOLR-9515 Update to Hadoop 3