Introduction to Hadoop Administration

INTRODUCTION
HADOOP
ADMINISTRATION
Knowledgebee Trainings

HADOOP A DISTRIBUTED
FILE SYSTEM
1. Introduction: Hadoop’s history and advantages
2. Architecture in detail
3. Hadoop in industry

Apache top level project, open-source implementation of frameworks for reliable,
scalable, distributed computing and data storage.
It is a flexible and highly-available architecture for large scale computation and data
processing on a network of commodity hardware.

BRIEF HISTORY OF HADOOP
Designed to answer the question: “How to process big data
with reasonable cost and time?”

SEARCH ENGINES IN 1990
1997
1996

Doug Cutting
2005: Doug Cutting and Michael J. Cafarella developed
Hadoop to support distribution for the Nutch search engine
project.
The project was funded by Yahoo.
2006: Yahoo gave the project to Apache
Software Foundation.

SOME HADOOP
MILESTONES
• 2008 - Hadoop Wins Terabyte Sort Benchmark (sorted 1 terabyte of data
in 209 seconds, compared to previous record of 297 seconds)
• 2009 - Avro and Chukwa became new members of Hadoop Framework
family
• 2010 - Hadoop's Hbase, Hive and Pig subprojects completed, adding more
computational power to Hadoop framework
• 2011 - ZooKeeper Completed
• 2013 - Hadoop 1.1.2 and Hadoop 2.0.3 alpha.
- Ambari, Cassandra, Mahout have been added

WHAT IS HADOOP?
• Hadoop:
• an open-source software framework that supports data-
intensive distributed applications, licensed under the Apache
v2 license.
• Goals / Requirements:
• Abstract and facilitate the storage and processing of large
and/or rapidly growing data sets
• Structured and non-structured data
• Simple programming models
• High scalability and availability
• Use commodity (cheap!) hardware with little redundancy
• Fault-tolerance
• Move computation rather than data

HADOOP ARCHITECTURE
• Distributed, with some centralization
• Main nodes of cluster are where most of the computational power and
storage of the system lies
• Main nodes run TaskTracker to accept and reply to MapReduce tasks,
and also DataNode to store needed blocks closely as possible
• Central control node runs NameNode to keep track of HDFS directories
& files, and JobTracker to dispatch compute tasks to TaskTracker
• Written in Java, also supports Python and Ruby

HADOOP ARCHITECTURE
• Hadoop Distributed Filesystem
• Tailored to needs of MapReduce
• Targeted towards many reads of filestreams
• Writes are more costly
• High degree of data replication (3x by default)
• No need for RAID on normal nodes
• Large blocksize (64MB)
• Location awareness of DataNodes in network

HADOOP ARCHITECTURE
NameNode:
• Stores metadata for the files, like the directory structure of a
typical FS.
• The server holding the NameNode instance is quite crucial, as
there is only one.
• Transaction log for file deletes/adds, etc. Does not use
transactions for whole blocks or file-streams, only metadata.
• Handles creation of more replica blocks when necessary after a
DataNode failure

HADOOP ARCHITECTURE
DataNode:
• Stores the actual data in HDFS
• Can run on any underlying filesystem (ext3/4, NTFS, etc)
• Notifies NameNode of what blocks it has
• NameNode replicates blocks 2x in local rack, 1x elsewhere

HADOOP ARCHITECTURE
MAPREDUCE ENGINE

HADOOP ARCHITECTURE
MapReduce Engine:
• JobTracker & TaskTracker
• JobTracker splits up data into smaller tasks(“Map”) and sends it to
the TaskTracker process in each node
• TaskTracker reports back to the JobTracker node and reports on
job progress, sends data (“Reduce”) or requests new jobs

HADOOP ARCHITECTURE
• None of these components are necessarily limited to using HDFS
• Many other distributed file-systems with quite different
architectures work
• Many other software packages besides Hadoop's MapReduce
platform make use of HDFS

HADOOP IN THE WILD
• Hadoop is in use at most organizations that handle big data:
o Yahoo!
o Facebook
o Amazon
o Netflix
o Etc…
• Some examples of scale:
o Yahoo!’s Search Webmap runs on 10,000 core Linux cluster
and powers Yahoo! Web search
o FB’s Hadoop cluster hosts 100+ PB of data (July, 2012) &
growing at ½ PB/day (Nov, 2012)

HADOOP IN THE WILD
• Advertisement (Mining user behavior to generate
recommendations)
• Searches (group related documents)
• Security (search for uncommon patterns)
Three main applications of Hadoop:

HADOOP IN THE WILD:
FACEBOOK MESSAGES
• Design requirements:
o Integrate display of email, SMS and chat
messages between pairs and groups of
users
o Strong control over who users receive
messages from
o Suited for production use between 500
million people immediately after launch
o Stringent latency & uptime
requirements

HADOOP IN THE WILD
• System requirements
o High write throughput
o Cheap, elastic storage
o Low latency
o High consistency (within a
single data center good
enough)
o Disk-efficient sequential and
random read performance

HADOOP IN THE WILD
• Classic alternatives
o These requirements typically met using large MySQL cluster &
caching tiers using Memcached
o Content on HDFS could be loaded into MySQL or Memcached if
needed by web tier
• Problems with previous solutions
o MySQL has low random write throughput… BIG problem for
messaging!
o Difficult to scale MySQL clusters rapidly while maintaining
performance
o MySQL clusters have high management overhead, require more
expensive hardware

HADOOP IN THE WILD
• Facebook’s solution
o Hadoop + HBase as foundations
o Improve & adapt HDFS and HBase to scale to FB’s workload and
operational considerations
 Major concern was availability: NameNode is SPOF & failover times
are at least 20 minutes
 Proprietary “AvatarNode”: eliminates SPOF, makes HDFS safe to
deploy even with 24/7 uptime requirement
 Performance improvements for realtime workload: RPC timeout.
Rather fail fast and try a different DataNode

DATA NODE
▪ A Block Sever
▪ Stores data in local file system
▪ Stores meta-data of a block - checksum
▪ Serves data and meta-data to clients
▪ Block Report
▪ Periodically sends a report of all existing blocks to
NameNode
▪ Facilitate Pipelining of Data
▪ Forwards data to other specified DataNodes

BLOCK PLACEMENT
▪ Replication Strategy
▪ One replica on local node
▪ Second replica on a remote rack
▪ Third replica on same remote rack
▪ Additional replicas are randomly placed
▪ Clients read from nearest replica

DATA CORRECTNESS
▪ Use Checksums to validate data – CRC32
▪ File Creation
▪ Client computes checksum per 512 byte
▪ DataNode stores the checksum
▪ File Access
▪ Client retrieves the data and checksum from DataNode
▪ If validation fails, client tries other replicas

INTER PROCESS COMMUNICATION
IPC/RPC (ORG.APACHE.HADOOP.IPC)
▪ Protocol
▪ JobClient <-------------> JobTracker
▪ TaskTracker <------------> JobTracker
▪ TaskTracker <-------------> Child
▪ JobTracker impliments both protocol and works as server in
both IPC
▪ TaskTracker implements the TaskUmbilicalProtocol; Child gets
task information and reports task status through it.
JobSubmissionProtocol
InterTrackerProtocol
TaskUmbilicalProtocol

JOBCLIENT.SUBMITJOB - 1
▪ Check input and output, e.g. check if the output directory is already
existing
▪ job.getInputFormat().validateInput(job);
▪ job.getOutputFormat().checkOutputSpecs(fs, job);
▪ Get InputSplits, sort, and write output to HDFS
▪ InputSplit[] splits = job.getInputFormat().
getSplits(job, job.getNumMapTasks());
▪ writeSplitsFile(splits, out); // out is $SYSTEMDIR/$JOBID/job.split

JOBCLIENT.SUBMITJOB - 2
▪ The jar file and configuration file will be uploaded to HDFS system
directory
▪ job.write(out); // out is $SYSTEMDIR/$JOBID/job.xml
▪ JobStatus status = jobSubmitClient.submitJob(jobId);
▪ This is an RPC invocation, jobSubmitClient is a proxy created in the initialization

DATA PIPELINING
▪ Client retrieves a list of DataNodes on which to place replicas of a block
▪ Client writes block to the first DataNode
▪ The first DataNode forwards the data to the next DataNode in the
Pipeline
▪ When all replicas are written, the client moves on to write the next
block in file

MAPREDUCE USAGE
▪ Log processing
▪ Web search indexing
▪ Ad-hoc queries

CLOSER LOOK
▪ MapReduce Component
▪ JobClient
▪ JobTracker
▪ TaskTracker
▪ Child
▪ Job Creation/Execution Process

MAPREDCE PROCESS
(ORG.APACHE.HADOOP.MAPRED)
▪ JobClient
▪ Submit job
▪ JobTracker
▪ Manage and schedule job, split job into tasks
▪ TaskTracker
▪ Start and monitor the task execution
▪ Child
▪ The process that really execute the task

JOB INITIALIZATION ON JOBTRACKER - 1
▪ JobTracker.submitJob(jobID) <-- receive RPC invocation request
▪ JobInProgress job = new JobInProgress(jobId, this, this.conf)
▪ Add the job into Job Queue
▪ jobs.put(job.getProfile().getJobId(), job);
▪ jobsByPriority.add(job);
▪ jobInitQueue.add(job);

JOB INITIALIZATION ON JOBTRACKER - 2
▪ Sort by priority
▪ resortPriority();
▪ compare the JobPrioity first, then compare the JobSubmissionTime
▪ Wake JobInitThread
▪ jobInitQueue.notifyall();
▪ job = jobInitQueue.remove(0);
▪ job.initTasks();

JOBINPROGRESS - 1
▪ JobInProgress(String jobid, JobTracker jobtracker, JobConf
default_conf);
▪ JobInProgress.initTasks()
▪ DataInputStream splitFile = fs.open(new Path(conf.get(“mapred.job.split.file”)));
// mapred.job.split.file --> $SYSTEMDIR/$JOBID/job.split

JOBINPROGRESS - 2
▪ splits = JobClient.readSplitFile(splitFile);
▪ numMapTasks = splits.length;
▪ maps[i] = new TaskInProgress(jobId, jobFile, splits[i], jobtracker, conf,
this, i);
▪ reduces[i] = new TaskInProgress(jobId, jobFile, splits[i], jobtracker, conf,
this, i);
▪ JobStatus --> JobStatus.RUNNING

JOBTRACKER TASK SCHEDULING - 1
▪ Task getNewTaskForTaskTracker(String taskTracker)
▪ Compute the maximum tasks that can be running on taskTracker
▪ int maxCurrentMap Tasks = tts.getMaxMapTasks();
▪ int maxMapLoad = Math.min(maxCurrentMapTasks, (int)Math.ceil(double)
remainingMapLoad/numTaskTrackers));

JOBTRACKER TASK SCHEDULING - 2
▪ int numMaps = tts.countMapTasks(); // running tasks number
▪ If numMaps < maxMapLoad, then more tasks can be allocated, then
based on priority, pick the first job from the jobsByPriority Queue,
create a task, and return to TaskTracker
▪ Task t = job.obtainNewMapTask(tts, numTaskTrackers);

START TASKTRACKER - 1
▪ initialize()
▪ Remove original local directory
▪ RPC initialization
▪ TaskReportServer = RPC.getServer(this, bindAddress, tmpPort, max, false, this, fConf);
▪ InterTrackerProtocol jobClient = (InterTrackerProtocol)
RPC.waitForProxy(InterTrackerProtocol.class, InterTrackerProtocol.versionID,
jobTrackAddr, this.fConf);

START TASKTRACKER - 2
▪ run();
▪ offerService();
▪ TaskTracker talks to JobTracker with HeartBeat message periodically
▪ HeatbeatResponse heartbeatResponse = transmitHeartBeat();

RUN TASK ON TASKTRACKER - 1
▪ TaskTracker.localizeJob(TaskInProgress tip);
▪ launchTasksForJob(tip, new JobConf(rjob.jobFile));
▪ tip.launchTask(); // TaskTracker.TaskInProgress
▪ tip.localizeTask(task); // create folder, symbol link
▪ runner = task.createRunner(TaskTracker.this);
▪ runner.start(); // start TaskRunner thread

RUN TASK ON TASKTRACKER - 2
▪ TaskRunner.run();
▪ Configure child process’ jvm parameters, i.e. classpath, taskid, taskReportServer’s
address & port
▪ Start Child Process
▪ runChild(wrappedCommand, workDir, taskid);

CHILD.MAIN()
▪ Create RPC Proxy, and execute RPC invocation
▪ TaskUmbilicalProtocol umbilical = (TaskUmbilicalProtocol)
RPC.getProxy(TaskUmbilicalProtocol.class, TaskUmbilicalProtocol.versionID,
address, defaultConf);
▪ Task task = umbilical.getTask(taskid);
▪ task.run(); // mapTask / reduceTask.run

FINISH JOB - 1
▪ Child
▪ task.done(umilical);
▪ RPC call: umbilical.done(taskId, shouldBePromoted)
▪ TaskTracker
▪ done(taskId, shouldPromote)
▪ TaskInProgress tip = tasks.get(taskid);
▪ tip.reportDone(shouldPromote);
▪ taskStatus.setRunState(TaskStatus.State.SUCCEEDED)

FINISH JOB - 2
▪ JobTracker
▪ TaskStatus report: status.getTaskReports();
▪ TaskInProgress tip = taskidToTIPMap.get(taskId);
▪ JobInProgress update JobStatus
▪ tip.getJob().updateTaskStatus(tip, report, myMetrics);
▪ One task of current job is finished
▪ completedTask(tip, taskStatus, metrics);
▪ If (this.status.getRunState() == JobStatus.RUNNING && allDone)
{this.status.setRunState(JobStatus.SUCCEEDED)}

RESULT
▪ Word Count
▪ hadoop jar hadoop-0.20.2-examples.jar wordcount <input dir> <output dir>
▪ Hive
▪ hive -f pagerank.hive

THANK YOU
Contact : Knowledgebee@beenovo.com

Introduction to Hadoop Administration

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Introduction to Hadoop Administration