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This project contains several diagrams describing Apache Hadoop internals (2.3.0 or later). Even if these diagrams are NOT specified in any formal or unambiguous language (e.g., UML), they should be reasonably understandable (here some diagram notation conventions) and useful for any person who want to grasp the main ideas behind Hadoop. Unfortunately, not all the internal details are covered by these diagrams. You are free to help :)

Actors	Tasks	Model of computation	Extra
Job Submitter Node Manager Resource Manager Application Master	Map Task Reduce Task Merger Input	Job Task Task Attempt Application Container	Async Dispatcher Localized Resource Container Allocator [AM] Container Launcher [AM] Containers Launcher [NM]

### Architecture Overview  ### Hadoop Configuration parameters Parameter | File | Default | Diagram(s) ------------- | ------------- | ------------- | ------------- `mapreduce.task.io.sort.mb` | `mapred-site.xml` | 100 | [MapTask > Shuffle](MapTask#post-execution---shuffle) | | | [MapTask > Execution](MapTask#execution) `mapreduce.map.sort.spill.percent` | `mapred-site.xml` | 0.80 | [MapTask > Shuffle](MapTask#post-execution---shuffle) | | | [MapTask > Execution](MapTask#execution) `mapreduce.task.io.sort.factor` | `mapred-site.xml` | 100 | [MapTask > Shuffle](MapTask#post-execution---shuffle) | | | [Merge](MapReduceMerge) | | | [ReduceTask > Shuffle](ReduceTask#shuffle---merge) `mapreduce.map.combine.minspills` | `mapred-site.xml` | 3 | [MapTask > Shuffle](MapTask#post-execution---shuffle) `mapreduce.job.reduces` | `mapred-site.xml` | 1 | [MapTask > Shuffle](MapTask#post-execution---shuffle) | | 0 | [Job > NEW => INITED](Job#new--inited-job_init) `mapreduce.cluster.local.dir` | `mapred-site.xml` | `${hadoop.tmp.dir}`/mapred/local | [MapTask > Shuffle](MapTask#post-execution---shuffle) `mapreduce.reduce.merge.memtomem.enabled` | `mapred-site.xml` | False | [Reduce Task > Shuffle](ReduceTask#shuffle) `mapreduce.framework.name` | `mapred-site.xml` | `yarn`/`local` | [Reduce Task > Shuffle](ReduceTask#shuffle) `mapreduce.reduce.shuffle.parallelcopies` | `mapred-site.xml` | 5 | [Reduce Task > Shuffle](ReduceTask#shuffle) `mapreduce.reduce.memory.totalbytes` | `mapred-site.xml` | `Runtime.maxMemory()` | [Reduce Task > Fetcher](ReduceTask#local-fetcher) `mapreduce.reduce.shuffle.memory.limit.percent` | `mapred-site.xml` | 0.25 | [Reduce Task > Fetcher](ReduceTask#local-fetcher) `mapreduce.job.ubertask.enable` | `mapred-site.xml` | False | [Job > NEW => INITED](Job#new--inited-job_init) `mapreduce.job.ubertask.maxmaps` | `mapred-site.xml` | 9 | [Job > NEW => INITED](Job#new--inited-job_init) `mapreduce.job.ubertask.maxreduces` | `mapred-site.xml` | 1 | [Job > NEW => INITED](Job#new--inited-job_init) `mapreduce.job.ubertask.maxbytes` | `mapred-site.xml` | `dfs.block.size` | [Job > NEW => INITED ](Job#new--inited-job_init) `mapreduce.map.
failures.maxpercent` | `mapred-site.xml` | 0 | [Job > RUNNING => {RUNNING, COMMITTING, FAIL ABORT}](Job#running--running-committing-fail-abort-job_task_completed) `mapreduce.reduce.
failures.maxpercent` | `mapred-site.xml` | 0 | [Job > RUNNING => {RUNNING, COMMITTING, FAIL ABORT}](Job#running--running-committing-fail-abort-job_task_completed) `mapreduce.map.memory.mb` | `mapred-site.xml` | 1024 | [Task Attempt > NEW => UNASSIGNED](TaskAttempt#new--unassigned-ta_schedule) `mapreduce.reduce.memory.mb` | `mapred-site.xml` | 1024 | [Task Attempt > NEW => UNASSIGNED](TaskAttempt#new--unassigned-ta_schedule) `scheduler.maximum-allocation-mb` | `yarn-site.xml` | 8192 | [Container Allocator](ContainerAllocator) `mapreduce.reduce.shuffle.merge.percent` | `mapred-site.xml` | 0.90 | [Reduce Task > Shuffle](ReduceTask#shuffle---merge)