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3. Hadoop is an open source framework which
is composed in java by apache software
foundation.
This framework is utilized to write software
application which requires to process
unfathomable measure of information (It
could handle with multi tera bytes of
information).
4. 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.
6. • 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
7. • 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
8. • 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
10. • 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
11. 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
12. 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
14. 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
15. • 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
16. • 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)
17. • Advertisement (Mining user behavior to generate
recommendations)
• Searches (group related documents)
• Security (search for uncommon patterns)
Three main applications of Hadoop:
18. • Non-realtime large dataset computing:
o NY Times was dynamically generating PDFs of articles
from 1851-1922
o Wanted to pre-generate & statically serve articles to
improve performance
o Using Hadoop + MapReduce running on EC2 / S3,
converted 4TB of TIFFs into 11 million PDF articles in
24 hrs
19. • 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
20. • 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
21. • 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
22. Distributed File System
Fault Tolerance
Open Data Format
Flexible Schema
Queryable Database
23. Need to process Multi Petabyte Datasets
Data may not have strict schema
Expensive to build reliability in each
application
Nodes fails everyday
Need common infrastructure
Very Large Distributed File System
Assumes Commodity Hardware
Optimized for Batch Processing
Runs on heterogeneous OS
24. 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
25. 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
26. 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
27. 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
28. MapReduce programming model
Framework for distributed processing of large data
sets
Pluggable user code runs in generic framework
Common design pattern in data processing
cat * | grep | sort | uniq -c | cat > file
input | map | shuffle | reduce | output