我在减少合并阶段遇到了一些性能问题，我想知道是否有人可以看看。我有一个 6 GB 数据集（文本），均匀分布在集群上，该数据集有两个键，然后我将它们 GroupBy 分成两个减速器（我正在使用级联）。所以每个reducer都有3GB的数据。我给每个 reducer 12 GB 内存，但我仍然看到 20 分钟的合并阶段。
两个问题：这个合并不应该完全在内存中完成（如果我有 12 GB 的堆）。即使没有内存合并，20 分钟似乎对于合并 3GB 来说太长了，尤其是在一个节点上有 12 个磁盘 (JBOD) 和 12 个内核的情况下。我想知道我是否将部分合并数据写入错误的位置（HDFS，与本地？）。
MAPRFS_BYTES_READ 和 MAPRFS_BYTES_WRITTEN 很有趣。初始数据集为 6GB（显示在 Map 列中）。不知何故，排序将其增加到 17GB，这似乎很奇怪。然后在减少阶段它从 MapRfs 读取 23GB，并写入 17GB。reduce阶段合并数据应该写入MapRFS还是本地FS？为什么大小会比初始数据集增长这么多（不使用压缩，它是纯文本）
Counter Map Reduce Total
Job Counters Aggregate execution time of mappers(ms) 0 0 29,887,359
Launched reduce tasks 0 0 2
Rack-local map tasks 0 0 4
Launched map tasks 0 0 353
Data-local map tasks 0 0 311
cascading.flow.SliceCounters Read_Duration 329,399 366,004 695,403
Tuples_Read 252,000,000 67,896,295 319,896,295
Tuples_Written 252,000,000 0 252,000,000
Process_End_Time 476,294,761,317,139 0 476,294,761,317,139
Write_Duration 2,713,840 0 2,713,840
Process_Begin_Time 476,294,753,764,176 2,698,557,228,678 478,993,310,992,854
FileSystemCounters MAPRFS_BYTES_READ 6,651,978,400 21,721,014,791 28,372,993,191
MAPRFS_BYTES_WRITTEN 17,044,716,578 17,044,701,398 34,089,417,976
FILE_BYTES_WRITTEN 19,046,005 107,748 19,153,753
Map-Reduce Framework Map input records 252,000,000 0 252,000,000
Reduce shuffle bytes 0 16,980,659,887 16,980,659,887
Spilled Records 252,000,000 0 252,000,000
Map output bytes 16,540,701,046 0 16,540,701,046
CPU_MILLISECONDS 18,861,020 7,640,360 26,501,380
Map input bytes 6,644,947,675 0 6,644,947,675
Combine input records 0 0 0
SPLIT_RAW_BYTES 97,428 0 97,428
Reduce input records 0 67,896,295 67,896,295
Reduce input groups 0 2 2
Combine output records 0 0 0
PHYSICAL_MEMORY_BYTES 324,852,019,200 15,041,486,848 339,893,506,048
Reduce output records 0 0 0
VIRTUAL_MEMORY_BYTES 626,863,038,464 26,729,230,336 653,592,268,800
Map output records 252,000,000 0 252,000,000
GC time elapsed (ms) 1,568,523 76,636 1,645,159
cascading.flow.StepCounters Tuples_Read 252,000,000 0 252,000,000
name value
fs.s3n.impl org.apache.hadoop.fs.s3native.NativeS3FileSystem
mapreduce.heartbeat.100 1000
mapred.task.cache.levels 2
hadoop.tmp.dir /tmp/hadoop-${user.name}
hadoop.native.lib true
map.sort.class org.apache.hadoop.util.QuickSort
mapreduce.jobtracker.recovery.dir /var/mapr/cluster/mapred/jobTracker/recovery
mapreduce.heartbeat.1000 10000
ipc.client.idlethreshold 4000
mapred.system.dir /var/mapr/cluster/mapred/jobTracker/system
mapreduce.cluster.reduce.userlog.retain-size 10485760
mapred.job.tracker.persist.jobstatus.hours 0
io.skip.checksum.errors false
fs.default.name maprfs:///
mapred.cluster.reduce.memory.mb -1
mapred.child.tmp ./tmp
fs.har.impl.disable.cache true
mapred.jobtracker.jobhistory.lru.cache.size 5
mapred.skip.reduce.max.skip.groups 0
cascading.flow.step.num 1
mapred.jobtracker.instrumentation org.apache.hadoop.mapred.JobTrackerMetricsInst
mapr.localvolumes.path /var/mapr/local
mapred.tasktracker.dns.nameserver default
io.sort.factor 50
mapred.output.value.groupfn.class cascading.tuple.hadoop.util.GroupingComparator
mapreduce.use.maprfs true
mapred.task.timeout 600000
mapred.max.tracker.failures 4
hadoop.rpc.socket.factory.class.default org.apache.hadoop.net.StandardSocketFactory
mapred.mapoutput.key.class cascading.tuple.io.TuplePair
fs.hdfs.impl org.apache.hadoop.hdfs.DistributedFileSystem
mapred.queue.default.acl-administer-jobs
mapred.output.key.class org.apache.hadoop.io.Text
mapred.skip.map.auto.incr.proc.count true
mapred.map.runner.class cascading.flow.hadoop.FlowMapper
mapreduce.job.complete.cancel.delegation.tokens true
mapreduce.tasktracker.heapbased.memory.management false
io.mapfile.bloom.size 1048576
tasktracker.http.threads 2
mapred.job.shuffle.merge.percent 0.70
cascading.flow.id 853276BF02049D394C31880B08C9E6CC
mapred.child.renice 10
fs.ftp.impl org.apache.hadoop.fs.ftp.FTPFileSystem
user.name jdavis
mapred.fairscheduler.smalljob.max.inputsize 10737418240
mapred.output.compress false
io.bytes.per.checksum 512
mapred.healthChecker.script.timeout 600000
topology.node.switch.mapping.impl org.apache.hadoop.net.ScriptBasedMapping
mapred.reduce.slowstart.completed.maps 0.95
mapred.reduce.max.attempts 4
fs.ramfs.impl org.apache.hadoop.fs.InMemoryFileSystem
mapr.localoutput.dir output
mapred.skip.map.max.skip.records 0
mapred.jobtracker.port 9001
mapred.cluster.map.memory.mb -1
mapreduce.tasktracker.prefetch.maptasks 1.0
hadoop.security.group.mapping org.apache.hadoop.security.ShellBasedUnixGroupsMapping
mapreduce.tasktracker.task.slowlaunch false
mapred.job.tracker.persist.jobstatus.dir /var/mapr/cluster/mapred/jobTracker/jobsInfo
mapred.jar /var/mapr/cluster/mapred/jobTracker/staging/jdavis/.staging/job_201210022148_0086/job.jar
fs.s3.buffer.dir ${hadoop.tmp.dir}/s3
job.end.retry.attempts 0
fs.file.impl org.apache.hadoop.fs.LocalFileSystem
cascading.app.name omeg
mapred.local.dir.minspacestart 0
mapred.output.compression.type RECORD
fs.mapr.working.dir /user/$USERNAME/
fs.maprfs.impl com.mapr.fs.MapRFileSystem
fs.https.impl cascading.tap.hadoop.io.HttpFileSystem
topology.script.number.args 100
io.mapfile.bloom.error.rate 0.005
mapred.cluster.max.reduce.memory.mb -1
mapred.max.tracker.blacklists 4
mapred.task.profile.maps 0-2
mapred.userlog.retain.hours 24
mapred.job.tracker.persist.jobstatus.active false
hadoop.security.authorization false
local.cache.size 10737418240
mapred.min.split.size 0
mapred.map.tasks 353
mapred.tasktracker.task-controller.config.overwrite true
cascading.app.appjar.path /home/jdavis/tmp/omeg.jar
mapred.output.value.class org.apache.hadoop.io.Text
mapred.partitioner.class cascading.tuple.hadoop.util.GroupingPartitioner
mapreduce.maprfs.use.compression true
mapred.job.queue.name default
mapreduce.tasktracker.reserved.physicalmemory.mb.low 0.90
cascading.group.comparator.size 3
ipc.server.listen.queue.size 128
group.name common
mapred.inmem.merge.threshold 0
job.end.retry.interval 30000
mapred.fairscheduler.smalljob.max.maps 10
mapred.skip.attempts.to.start.skipping 2
fs.checkpoint.dir ${hadoop.tmp.dir}/dfs/namesecondary
mapred.reduce.tasks 2
mapred.merge.recordsBeforeProgress 10000
mapred.userlog.limit.kb 0
mapred.job.reduce.memory.mb -1
webinterface.private.actions true
io.sort.spill.percent 0.99
mapred.job.shuffle.input.buffer.percent 0.80
mapred.job.name [853276BF02049D394C31880B08C9E6CC/DCB7B555F1FC65C767B8E2CD716607AA] copyr/(1/1) /user/jdavis/ctest/end
mapred.map.tasks.speculative.execution false
hadoop.util.hash.type murmur
mapred.map.max.attempts 4
mapreduce.job.acl-view-job
mapred.job.tracker.handler.count 10
mapred.input.format.class cascading.tap.hadoop.io.MultiInputFormat
mapred.tasktracker.expiry.interval 600000
mapred.jobtracker.maxtasks.per.job -1
mapred.jobtracker.job.history.block.size 3145728
keep.failed.task.files false
mapred.output.format.class org.apache.hadoop.mapred.TextOutputFormat
ipc.client.tcpnodelay false
mapred.task.profile.reduces 0-2
mapred.output.compression.codec org.apache.hadoop.io.compress.DefaultCodec
io.map.index.skip 0
mapred.working.dir /user/jdavis
ipc.server.tcpnodelay false
hadoop.proxyuser.root.hosts
mapred.reducer.class cascading.flow.hadoop.FlowReducer
cascading.app.id A593B4669179BB6F06771249E7ADFA48
mapred.used.genericoptionsparser true
jobclient.progress.monitor.poll.interval 1000
mapreduce.tasktracker.jvm.idle.time 10000
mapred.job.map.memory.mb -1
hadoop.logfile.size 10000000
mapred.reduce.tasks.speculative.execution false
mapreduce.job.dir maprfs:/var/mapr/cluster/mapred/jobTracker/staging/jdavis/.staging/job_201210022148_0086
mapreduce.tasktracker.outofband.heartbeat true
mapreduce.reduce.input.limit -1
mapred.tasktracker.ephemeral.tasks.ulimit 4294967296>
fs.s3n.block.size 67108864
fs.inmemory.size.mb 200
mapred.fairscheduler.smalljob.max.reducers 10
hadoop.security.authentication simple
fs.checkpoint.period 3600
cascading.flow.step.id DCB7B555F1FC65C767B8E2CD716607AA
mapred.job.reuse.jvm.num.tasks -1
mapred.jobtracker.completeuserjobs.maximum 5
mapreduce.cluster.map.userlog.retain-size 10485760
mapred.task.tracker.task-controller org.apache.hadoop.mapred.LinuxTaskController
mapred.output.key.comparator.class cascading.tuple.hadoop.util.GroupingSortingComparator
fs.s3.maxRetries 4
mapred.cluster.max.map.memory.mb -1
mapred.mapoutput.value.class cascading.tuple.Tuple
mapred.map.child.java.opts -XX:ErrorFile=/opt/cores/mapreduce_java_error%p.log
mapred.job.tracker.history.completed.location /var/mapr/cluster/mapred/jobTracker/history/done
mapred.local.dir /tmp/mapr-hadoop/mapred/local
fs.hftp.impl org.apache.hadoop.hdfs.HftpFileSystem
fs.trash.interval 0
fs.s3.sleepTimeSeconds 10
mapred.submit.replication 10
fs.har.impl org.apache.hadoop.fs.HarFileSystem
mapreduce.heartbeat.10 300
cascading.version Concurrent, Inc - Cascading 2.0.5
mapred.map.output.compression.codec org.apache.hadoop.io.compress.DefaultCodec
mapred.tasktracker.dns.interface default
hadoop.proxyuser.root.groups root
mapred.job.tracker maprfs:///
mapreduce.job.submithost c10-m001.wowrack.upstream.priv
mapreduce.tasktracker.cache.local.numberdirectories 10000
io.seqfile.sorter.recordlimit 1000000
mapreduce.heartbeat.10000 100000
mapred.line.input.format.linespermap 1
mapred.jobtracker.taskScheduler org.apache.hadoop.mapred.FairScheduler
mapred.tasktracker.instrumentation org.apache.hadoop.mapred.TaskTrackerMetricsInst
mapred.tasktracker.taskmemorymanager.killtask.maxRSS false
mapred.child.taskset true
jobclient.completion.poll.interval 5000
mapred.fairscheduler.smalljob.max.reducer.inputsize 1073741824
mapred.local.dir.minspacekill 0
io.sort.record.percent 0.28
mapr.localspill.dir spill
io.compression.codec.lzo.class com.hadoop.compression.lzo.LzoCodec
fs.kfs.impl org.apache.hadoop.fs.kfs.KosmosFileSystem
mapred.tasktracker.reduce.tasks.maximum (CPUS > 2) ? (CPUS * 0.70): 1
mapred.temp.dir ${hadoop.tmp.dir}/mapred/temp
mapred.tasktracker.ephemeral.tasks.maximum 1
fs.checkpoint.edits.dir ${fs.checkpoint.dir}
mapred.tasktracker.tasks.sleeptime-before-sigkill 5000
mapred.job.reduce.input.buffer.percent 0.0
mapred.tasktracker.indexcache.mb 10
mapreduce.task.classpath.user.precedence false
mapreduce.job.split.metainfo.maxsize -1
hadoop.logfile.count 10
fs.automatic.close true
mapred.skip.reduce.auto.incr.proc.count true
mapreduce.job.submithostaddress 10.100.0.99
mapred.child.oom_adj 10
io.seqfile.compress.blocksize 1000000
fs.s3.block.size 67108864
mapred.tasktracker.taskmemorymanager.monitoring-interval 3000
mapreduce.tasktracker.volume.healthcheck.interval 60000
mapred.cluster.ephemeral.tasks.memory.limit.mb 200
mapreduce.jobtracker.staging.root.dir /var/mapr/cluster/mapred/jobTracker/staging
mapred.acls.enabled false
mapred.queue.default.state RUNNING
mapred.fairscheduler.smalljob.schedule.enable false
mapred.queue.names default
fs.hsftp.impl org.apache.hadoop.hdfs.HsftpFileSystem
mapred.fairscheduler.eventlog.enabled false
mapreduce.jobtracker.recovery.maxtime 480
mapred.task.tracker.http.address 0.0.0.0:50060
mapreduce.jobtracker.inline.setup.cleanup false
mapred.reduce.parallel.copies 40
io.seqfile.lazydecompress true
mapred.tasktracker.ephemeral.tasks.timeout 10000
mapred.output.dir maprfs:/user/jdavis/ctest/end
mapreduce.tasktracker.group root
hadoop.workaround.non.threadsafe.getpwuid false
io.sort.mb 512
mapred.reduce.child.java.opts -Xmx12000m
ipc.client.connection.maxidletime 10000
mapred.compress.map.output false
hadoop.security.uid.cache.secs 14400
mapred.task.tracker.report.address 127.0.0.1:0
mapred.healthChecker.interval 60000
ipc.client.kill.max 10
ipc.client.connect.max.retries 10
fs.http.impl cascading.tap.hadoop.io.HttpFileSystem
fs.s3.impl org.apache.hadoop.fs.s3.S3FileSystem
mapred.fairscheduler.assignmultiple true
mapred.user.jobconf.limit 5242880
mapred.input.dir maprfs:/user/jdavis/ctest/mid
mapred.job.tracker.http.address 0.0.0.0:50030
io.file.buffer.size 131072
mapred.jobtracker.restart.recover true
io.serializations cascading.tuple.hadoop.TupleSerialization,org.apache.hadoop.io.serializer.WritableSerialization
mapreduce.use.fastreduce false
mapred.reduce.copy.backoff 300
mapred.task.profile false
mapred.jobtracker.retiredjobs.cache.size 300
jobclient.output.filter FAILED
mapred.tasktracker.map.tasks.maximum (CPUS > 2) ? (CPUS * 0.80) : 1
io.compression.codecs org.apache.hadoop.io.compress.GzipCodec,org.apache.hadoop.io.compress.DefaultCodec,org.apache.hadoop.io.compress.BZip2Codec,com.hadoop.compression.lzo.LzoCodec,com.hadoop.compression.lzo.LzopCodec
fs.checkpoint.size 67108864
cascading.sort.comparator.size 3
2012-10-02 19:30:50,676 INFO org.apache.hadoop.metrics.jvm.JvmMetrics: Initializing JVM Metrics with processName=SHUFFLE, sessionId=
2012-10-02 19:30:50,737 INFO org.apache.hadoop.mapreduce.util.ProcessTree: setsid exited with exit code 0
2012-10-02 19:30:50,742 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: /proc/<pid>/status does not have information about swap space used(VmSwap). Can not track swap usage of a task.
2012-10-02 19:30:50,742 INFO org.apache.hadoop.mapred.Task: Using ResourceCalculatorPlugin : org.apache.hadoop.mapreduce.util.LinuxResourceCalculatorPlugin@27b62aab
2012-10-02 19:30:50,903 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 9115 may have finished in the interim.
2012-10-02 19:31:01,663 INFO org.apache.hadoop.mapred.Merger: Merging 37 sorted segments
2012-10-02 19:31:01,672 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 36 segments left of total size: 1204882102 bytes
2012-10-02 19:31:03,079 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 7596 may have finished in the interim.
2012-10-02 19:31:15,487 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 4803 may have finished in the interim.
2012-10-02 19:31:15,489 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 11069 may have finished in the interim.
2012-10-02 19:33:37,821 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 20846 may have finished in the interim.
2012-10-02 19:33:59,274 INFO org.apache.hadoop.mapred.Merger: Merging 35 sorted segments
2012-10-02 19:33:59,275 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 35 segments left of total size: 1176895576 bytes
2012-10-02 19:34:02,131 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 21791 may have finished in the interim.
2012-10-02 19:34:29,927 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 22847 may have finished in the interim.
2012-10-02 19:36:32,181 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 30438 may have finished in the interim.
2012-10-02 19:37:18,243 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 3852 may have finished in the interim.
2012-10-02 19:37:26,292 INFO org.apache.hadoop.mapred.Merger: Merging 37 sorted segments
2012-10-02 19:37:26,293 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 37 segments left of total size: 1233203028 bytes
2012-10-02 19:39:07,695 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 9813 may have finished in the interim.
2012-10-02 19:39:10,764 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 10045 may have finished in the interim.
2012-10-02 19:39:56,829 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 17383 may have finished in the interim.
2012-10-02 19:40:18,295 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 19584 may have finished in the interim.
2012-10-02 19:40:32,307 INFO org.apache.hadoop.mapred.Merger: Merging 58 sorted segments
2012-10-02 19:40:32,308 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 44 segments left of total size: 1206978885 bytes
2012-10-02 19:41:35,154 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 26361 may have finished in the interim.
2012-10-02 19:43:53,644 INFO org.apache.hadoop.mapred.Merger: Merging 56 sorted segments
2012-10-02 19:43:53,645 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 56 segments left of total size: 1217287352 bytes
2012-10-02 19:46:55,246 INFO org.apache.hadoop.mapred.Merger: Merging 44 sorted segments
2012-10-02 19:46:55,246 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 44 segments left of total size: 1221163604 bytes
2012-10-02 19:49:57,894 INFO org.apache.hadoop.mapred.Merger: Merging 85 sorted segments
2012-10-02 19:49:57,895 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 62 segments left of total size: 1229975233 bytes
2012-10-02 19:52:09,914 WARN org.apache.hadoop.mapreduce.util.ProcfsBasedProcessTree: The process 25247 may have finished in the interim.
2012-10-02 19:52:52,620 INFO org.apache.hadoop.mapred.Merger: Merging 1 sorted segments
2012-10-02 19:52:52,620 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 1 segments left of total size: 32065409 bytes
2012-10-02 19:52:53,327 INFO org.apache.hadoop.mapred.Merger: Merging 8 sorted segments
2012-10-02 19:52:53,345 INFO org.apache.hadoop.mapred.Merger: Down to the last merge-pass, with 8 segments left of total size: 8522450575 bytes
2012-10-02 19:52:53,366 INFO cascading.flow.hadoop.FlowReducer: cascading version: Concurrent, Inc - Cascading 2.0.5