首页 > 代码库 > reduce端缓存数据过多出现FGC，导致reduce生成的数据无法写到hdfs
reduce端缓存数据过多出现FGC，导致reduce生成的数据无法写到hdfs
搜索推荐有一个job，1000多个map，200个reduce，运行到最后只剩一个reduce（10.39.6.130上）的时候，出现以下异常，导致job失败：
2014-12-04 15:49:04,297 INFO [main] org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 12 segments left of total size: 11503294914 bytes 2014-12-04 15:49:04,314 INFO [main] org.apache.hadoop.conf.Configuration.deprecation: mapred.task.id is deprecated. Instead, use mapreduce.task.attempt.id 2014-12-04 15:49:04,394 INFO [main] org.apache.hadoop.io.compress.CodecPool: Got brand-new compressor [.lzo_deflate] 2014-12-04 16:02:26,889 WARN [ResponseProcessor for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086] org.apache.hadoop.hdfs.DFSClient: DFSOutputStream ResponseProcessor exception for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 java.io.IOException: Bad response ERROR for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 from datanode 10.39.5.193:50010 at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:819) 2014-12-04 16:02:26,889 WARN [ResponseProcessor for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223] org.apache.hadoop.hdfs.DFSClient: DFSOutputStream ResponseProcessor exception for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 java.io.IOException: Bad response ERROR for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 from datanode 10.39.1.90:50010 at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:819) 2014-12-04 16:02:26,891 WARN [DataStreamer for file /dw_ext/recmd/mds6/mds_filter_relation_10/20141203/_temporary/1/_temporary/attempt_1415948652989_195149_r_000158_3/user-r-00158 block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086] org.apache.hadoop.hdfs.DFSClient: Error Recovery for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 in pipeline 10.39.6.130:50010, 10.39.5.185:50010, 10.39.5.193:50010: bad datanode 10.39.5.193:50010 2014-12-04 16:02:26,891 WARN [DataStreamer for file /dw_ext/recmd/mds6/mds_filter_relation_10/20141203/_temporary/1/_temporary/attempt_1415948652989_195149_r_000158_3/exposure-r-00158 block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223] org.apache.hadoop.hdfs.DFSClient: Error Recovery for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 in pipeline 10.39.6.130:50010, 10.39.1.89:50010, 10.39.1.90:50010: bad datanode 10.39.1.90:50010java.io.EOFException: Premature EOF: no length prefix available at org.apache.hadoop.hdfs.protocolPB.PBHelper.vintPrefixed(PBHelper.java:1987) at org.apache.hadoop.hdfs.protocol.datatransfer.PipelineAck.readFields(PipelineAck.java:176) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:796)
2014-12-04 16:05:23,743 FATAL [main] org.apache.hadoop.mapred.YarnChild: Error running child : java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Arrays.java:2734)
at java.util.Vector.ensureCapacityHelper(Vector.java:226)
at java.util.Vector.add(Vector.java:728)
at rec.CommonUtil.pack_Treeset(CommonUtil.java:395)
at rec.ConvertExposure10$MyReducer.collect_exposure(ConvertExposure10.java:259)
at rec.ConvertExposure10$MyReducer.reduce(ConvertExposure10.java:329)
at rec.ConvertExposure10$MyReducer.reduce(ConvertExposure10.java:234)
at org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:444)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:392)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:167)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:396)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1550)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:162)从异常上看，首先是reduce在往hdfs写数据时，发现建pipeline时，没有收到pipeline上最后一个节点的回应：
2014-12-04 16:02:26,889 WARN [ResponseProcessor for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086] org.apache.hadoop.hdfs.DFSClient: DFSOutputStream ResponseProcessor exception for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 java.io.IOException: Bad response ERROR for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 from datanode 10.39.5.193:50010 at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:819) 2014-12-04 16:02:26,889 WARN [ResponseProcessor for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223] org.apache.hadoop.hdfs.DFSClient: DFSOutputStream ResponseProcessor exception for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 java.io.IOException: Bad response ERROR for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 from datanode 10.39.1.90:50010 at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:819) 2014-12-04 16:02:26,891 WARN [DataStreamer for file /dw_ext/recmd/mds6/mds_filter_relation_10/20141203/_temporary/1/_temporary/attempt_1415948652989_195149_r_000158_3/user-r-00158 block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086] org.apache.hadoop.hdfs.DFSClient: Error Recovery for block BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 in pipeline 10.39.6.130:50010, 10.39.5.185:50010, 10.39.5.193:50010: bad datanode 10.39.5.193:50010 2014-12-04 16:02:26,891 WARN [DataStreamer for file /dw_ext/recmd/mds6/mds_filter_relation_10/20141203/_temporary/1/_temporary/attempt_1415948652989_195149_r_000158_3/exposure-r-00158 block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223] org.apache.hadoop.hdfs.DFSClient: Error Recovery for block BP-1386326728-10.39.2.131-1382089338395:blk_1394153869_320473223 in pipeline 10.39.6.130:50010, 10.39.1.89:50010, 10.39.1.90:50010: bad datanode 10.39.1.90:50010java.io.EOFException: Premature EOF: no length prefix available at org.apache.hadoop.hdfs.protocolPB.PBHelper.vintPrefixed(PBHelper.java:1987) at org.apache.hadoop.hdfs.protocol.datatransfer.PipelineAck.readFields(PipelineAck.java:176) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer$ResponseProcessor.run(DFSOutputStream.java:796)这里以写block：blk_1394149732_320469086为例，pipeline[10.39.6.130:50010, 10.39.5.185:50010, 10.39.5.193:50010]上面的最后一个DN是10.39.5.193，到10.39.5.193查看该block的日志信息：2014-12-04 16:00:57,424 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Exception for BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.5.193:50010 remote=/10.39.5.185:58225] at org.apache.hadoop.net.SocketIOWithTimeout.doIO(SocketIOWithTimeout.java:164) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:161) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:131) at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) at java.io.BufferedInputStream.read1(BufferedInputStream.java:258) at java.io.BufferedInputStream.read(BufferedInputStream.java:317) at java.io.DataInputStream.read(DataInputStream.java:132) at org.apache.hadoop.io.IOUtils.readFully(IOUtils.java:192) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doReadFully(PacketReceiver.java:213) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doRead(PacketReceiver.java:134) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.receiveNextPacket(PacketReceiver.java:109) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receivePacket(BlockReceiver.java:446) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receiveBlock(BlockReceiver.java:702) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:739) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:124) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:232) at java.lang.Thread.run(Thread.java:662) 2014-12-04 16:00:57,424 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: PacketResponder: BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086, type=LAST_IN_PIPELINE, downstreams=0:[]: Thread is interrupted.java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.5.193:50010 remote=/10.39.5.185:58225]那我们来看以下pipeline上第二个节点10.39.5.185，dn日志如下：2014-12-04 16:00:57,988 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: PacketResponder: BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086, type=HAS_DOWNSTREAM_IN_PIPELINE java.io.EOFException: Premature EOF: no length prefix available at org.apache.hadoop.hdfs.protocolPB.PBHelper.vintPrefixed(PBHelper.java:1987) at org.apache.hadoop.hdfs.protocol.datatransfer.PipelineAck.readFields(PipelineAck.java:176) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver$PacketResponder.run(BlockReceiver.java:1083) at java.lang.Thread.run(Thread.java:662) 2014-12-04 16:00:58,008 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Exception for BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.5.185:50010 remote=/10.39.6.130:59083] at org.apache.hadoop.net.SocketIOWithTimeout.doIO(SocketIOWithTimeout.java:164) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:161) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:131) at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) at java.io.BufferedInputStream.read1(BufferedInputStream.java:258) at java.io.BufferedInputStream.read(BufferedInputStream.java:317) at java.io.DataInputStream.read(DataInputStream.java:132) at org.apache.hadoop.io.IOUtils.readFully(IOUtils.java:192) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doReadFully(PacketReceiver.java:213) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doRead(PacketReceiver.java:134) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.receiveNextPacket(PacketReceiver.java:109) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receivePacket(BlockReceiver.java:446) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receiveBlock(BlockReceiver.java:702) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:739) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:124) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:232) at java.lang.Thread.run(Thread.java:662) 2014-12-04 16:00:58,009 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: PacketResponder: BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086, type=HAS_DOWNSTREAM_IN_PIPELINE: Thread is interrupted.java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.5.185:50010 remote=/10.39.6.130:59083]2014-12-04 16:00:59,987 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Exception for BP-1386326728-10.39.2.131-1382089338395:blk_1394149732_320469086 java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.6.130:50010 remote=/10.39.6.130:45259] at org.apache.hadoop.net.SocketIOWithTimeout.doIO(SocketIOWithTimeout.java:164) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:161) at org.apache.hadoop.net.SocketInputStream.read(SocketInputStream.java:131) at java.io.BufferedInputStream.fill(BufferedInputStream.java:218) at java.io.BufferedInputStream.read1(BufferedInputStream.java:258) at java.io.BufferedInputStream.read(BufferedInputStream.java:317) at java.io.DataInputStream.read(DataInputStream.java:132) at org.apache.hadoop.io.IOUtils.readFully(IOUtils.java:192) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doReadFully(PacketReceiver.java:213) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.doRead(PacketReceiver.java:134) at org.apache.hadoop.hdfs.protocol.datatransfer.PacketReceiver.receiveNextPacket(PacketReceiver.java:109) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receivePacket(BlockReceiver.java:446) at org.apache.hadoop.hdfs.server.datanode.BlockReceiver.receiveBlock(BlockReceiver.java:702) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:739) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.opWriteBlock(Receiver.java:124) at org.apache.hadoop.hdfs.protocol.datatransfer.Receiver.processOp(Receiver.java:71) at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:232) at java.lang.Thread.run(Thread.java:662)
但是根据日志信息，10.39.6.130的DN也是在等待Packet，但是一直等到超时也没等到：
java.net.SocketTimeoutException: 60000 millis timeout while waiting for channel to be ready for read. ch : java.nio.channels.SocketChannel[connected local=/10.39.6.130:50010 remote=/10.39.6.130:45259]看来不是10.39.6.130节点DN的问题，如果pipeline上面三个DN都没有问题，那问题肯定就出在dfsclient端了，也就是reduce任务在往hdfs写数据的时候根本就没有写得出去，在dfsclient上面就给堵住了，接下来查看dfsclient，也就是reduce任务进程的执行情况：
在10.39.6.130上，根据任务id：attempt_1415948652989_195149_r_000158_3 找到进程id 31050，查看内存使用情况：
jstat -gcutil 31050 1000：
S0 S1 E O P YGC YGCT FGC FGCT GCT
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 0.00 92.98 66.32 111 16.825 10 25.419 42.244
68.95 0.00 26.75 100.00 66.32 111 16.825 10 25.419 42.244
0.00 0.00 31.85 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 35.37 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 40.64 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 45.35 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 48.87 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 54.14 100.00 68.16 111 16.825 10 44.767 61.591
0.00 0.00 58.85 100.00 68.16 111 16.825 10 44.767 61.591
果然，JVM老年代被占满，不断执行FGC，直接stop the world，导致JVM没法对外提供服务，导致dfsclient挂起，一直不能往pipeline上面的节点写Packet，直到socket超时。
根据reduce任务最后的日志，也从侧面验证了这种观点：
Error running child : java.lang.OutOfMemoryError: Java heap space
既然是OOM导致的job失败，那是什么对象导致的内存泄露呢：
执行：jmap -histo:live 31050 > jmap.log
cat jmap.log :
num #instances #bytes class name
----------------------------------------------
1: 71824177 2872967080 java.util.TreeMap$Entry
2: 71822939 1723750536 java.lang.Long
3: 10684 24777776 [B
4: 47174 6425152 <methodKlass>
5: 47174 6408120 <constMethodKlass>
6: 3712 4429776 <constantPoolKlass>
7: 66100 3979224 <symbolKlass>
8: 3712 2938192 <instanceKlassKlass>
9: 3125 2562728 <constantPoolCacheKlass>
10: 3477 1267752 [I
11: 12923 1180224 [C
12: 1794 772488 <methodDataKlass>
13: 13379 428128 java.lang.String
14: 4034 419536 java.lang.Class
15: 6234 410312 [S
16: 6409 352576 [[I
17: 7567 242144 java.util.HashMap$Entry
18: 293 171112 <objArrayKlassKlass>
19: 4655 148960 java.util.Hashtable$Entry
20: 1535 135080 java.lang.reflect.Method
21: 842 121696 [Ljava.util.HashMap$Entry;
果然啊，reduce代码中使用了TreeMap，往里面放置了大量对象，导致出现OOM，TreeMap的Entry就站用了2.8G内存，而我们reduce设置的内存也就1.5G。
reduce端缓存数据过多出现FGC，导致reduce生成的数据无法写到hdfs
声明：以上内容来自用户投稿及互联网公开渠道收集整理发布，本网站不拥有所有权，未作人工编辑处理，也不承担相关法律责任，若内容有误或涉及侵权可进行投诉： 投诉/举报 工作人员会在5个工作日内联系你，一经查实，本站将立刻删除涉嫌侵权内容。