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Apache Hadoop

A comprehensive deep-dive into Apache Hadoop—the open-source distributed computing framework that democratized big data processing and built upon the foundations laid by Google’s GFS and MapReduce.
Course Duration: 14-18 hours Level: Intermediate to Advanced Prerequisites: Basic distributed systems knowledge, understanding of MapReduce concepts Outcome: Deep understanding of Hadoop architecture, HDFS, YARN, MapReduce, and ecosystem

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Why Study Hadoop?

Industry Standard

De facto big data platform. Powers data infrastructure at thousands of companies worldwide.

Interview Essential

Critical for data engineering and backend roles. Understanding Hadoop is essential for system design interviews.

Ecosystem Foundation

Foundation for Spark, Hive, HBase, and modern data tools. Understanding Hadoop helps you master the entire ecosystem.

Real-World Scale

Learn how Yahoo, Facebook, and others process petabytes of data daily with commodity hardware.

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What You’ll Learn

┌─────────────────────────────────────────────────────────────┐
│                  HADOOP MASTERY                             │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│ Chapter 1: Introduction & Origins                          │
│ • Hadoop's relationship to GFS and MapReduce               │
│ • Why Hadoop was created                                    │
│ • Design goals and philosophy                              │
│ • Ecosystem overview                                        │
│                                                             │
│ Chapter 2: HDFS Architecture                                │
│ • NameNode and DataNode design                             │
│ • How HDFS differs from GFS                                │
│ • Block replication and placement                          │
│ • Read and write data flows                                │
│                                                             │
│ Chapter 3: MapReduce Framework                              │
│ • Programming model deep dive                               │
│ • Job execution and task management                        │
│ • Shuffle and sort mechanisms                              │
│ • Optimization techniques                                   │
│                                                             │
│ Chapter 4: YARN Resource Management                         │
│ • ResourceManager and NodeManager                           │
│ • Container-based execution                                 │
│ • Scheduling algorithms                                     │
│ • Multi-tenancy support                                     │
│                                                             │
│ Chapter 5: Hadoop Ecosystem                                 │
│ • Hive: SQL on Hadoop                                       │
│ • Pig: Data flow language                                   │
│ • HBase: NoSQL database                                     │
│ • Spark integration and beyond                             │
│                                                             │
│ Chapter 6: Fault Tolerance                                  │
│ • HDFS failure handling                                     │
│ • MapReduce task recovery                                   │
│ • NameNode HA configurations                               │
│ • Data integrity and checksums                             │
│                                                             │
│ Chapter 7: Performance & Tuning                             │
│ • Performance bottlenecks                                   │
│ • Optimization strategies                                   │
│ • Benchmarks and best practices                            │
│ • JVM tuning and compression                               │
│                                                             │
│ Chapter 8: Production Deployment                            │
│ • Cluster sizing and planning                               │
│ • Monitoring and alerting                                   │
│ • Security (Kerberos, encryption)                          │
│ • Real-world use cases                                      │
│                                                             │
└─────────────────────────────────────────────────────────────┘

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Key Concepts Covered

Master HDFS architecture, how it implements GFS concepts in Java, and the differences between NameNode/DataNode and GFS Master/Chunkserver. Learn block replication strategies and fault tolerance mechanisms.
Deep dive into the MapReduce programming paradigm, how jobs are executed across clusters, the shuffle and sort phase, and how to write efficient MapReduce applications.
Understand how YARN decouples resource management from data processing, enabling Hadoop to run diverse workloads beyond MapReduce including Spark, Flink, and custom applications.
Study how Hadoop handles failures in a cluster of thousands of nodes, including NameNode HA, automatic block re-replication, and speculative execution of tasks.
Learn how Hadoop optimizes computation by moving processing to data rather than data to processing, reducing network bandwidth and improving performance dramatically.
Explore how Hive, Pig, HBase, Spark, and other tools build on Hadoop’s foundation to provide SQL, streaming, real-time processing, and more.

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Who This Course Is For

Big Data Engineers
  • Build and maintain Hadoop clusters
  • Design data processing pipelines
  • Optimize MapReduce and Spark jobs
  • Implement ETL workflows at scale
What You’ll Gain:
  • Production-ready Hadoop knowledge
  • Performance tuning expertise
  • Troubleshooting skills

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Prerequisites

Recommended Background:
  • Basic understanding of distributed systems
  • Familiarity with MapReduce concepts
  • Knowledge of Java programming (helpful)
  • Understanding of Linux file systems
Not Required But Helpful:
  • GFS paper knowledge
  • Experience with cloud computing
  • SQL and database concepts
  • Python or Scala programming

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Course Structure

Each chapter includes:

Theory

Deep conceptual explanations with comprehensive diagrams

Architecture

Component interactions and data flow analysis

Interview Prep

4-5 questions per chapter at various difficulty levels

Real-World Examples

Production insights from Yahoo, Facebook, and others

Visual Learning

ASCII diagrams, flowcharts, and architectural visuals

Key Takeaways

Summary sections highlighting critical concepts

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Learning Path

1

Understand the Origins

Start with Chapter 1 to learn how Hadoop evolved from Google’s GFS and MapReduce papers and why it became open source.
2

Master HDFS

Chapter 2 covers the distributed file system. Learn how HDFS stores petabytes reliably and efficiently.
3

Learn MapReduce

Chapter 3 dives into the programming model. Understand how to process massive datasets in parallel.
4

Explore YARN

Chapter 4 covers resource management. Learn how Hadoop 2.0 evolved beyond MapReduce-only processing.
5

Discover the Ecosystem

Chapter 5 explores tools built on Hadoop. See how Hive, Pig, HBase, and Spark extend capabilities.
6

Handle Failures

Chapter 6 covers fault tolerance. Learn how Hadoop maintains reliability despite constant failures.
7

Optimize Performance

Chapter 7 analyzes tuning techniques. Understand bottlenecks and optimization strategies.
8

Deploy to Production

Chapter 8 covers real-world deployment. Learn cluster management, monitoring, and operational best practices.

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Chapter-by-Chapter Deep Overview

The rest of this course is structured like a research-style walkthrough of Hadoop’s major subsystems. This section gives you paper-level notes for each chapter so you can treat this track almost like reading a series of system design papers.

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Chapter 2: HDFS Architecture – Storage for Web-Scale Data

Goals of HDFS:
  • Scale: Store petabytes of data across thousands of commodity machines.
  • Reliability: Survive constant hardware failures without losing data.
  • Throughput over latency: Optimize for large sequential reads/writes, not single-record lookups.
  • Simplicity: Provide a small set of operations (create, append, list, delete) with relaxed semantics.
Core Components: 
                HDFS HIGH-LEVEL VIEW

   ┌───────────────────────────────────────────────┐
   │                   Client                     │
   └───────────────┬──────────────────────────────┘
                   │ 1. metadata ops (open, create,
                   │    list, delete)
                   │
           ┌───────▼───────┐
           │   NameNode    │
           │  (metadata)   │
           └───────┬───────┘
                   │ 2. block locations
                   │
    ┌───────────────▼───────────────┐
    │         DataNodes (N)         │
    │  (actual block data, 3x rep) │
    └───────────────────────────────┘
  • NameNode: In-memory namespace tree (/user/alice/logs/...) and block mapping (file → [block IDs] → [DataNodes]).
  • DataNodes: Store block replicas as local files; periodically send block reports and heartbeats to the NameNode.
  • Secondary NameNode / Checkpoint Node: Periodically merges the NameNode’s edit log with the fsimage to keep metadata compact.
Block Management:
  • Files are split into large blocks (often 128MB/256MB+).
  • Each block is replicated (default replication factor = 3) across different nodes and racks.
  • NameNode tracks which DataNodes host replicas; DataNodes are largely stateless.
BLOCK PLACEMENT (SIMPLE HEURISTIC)

- Replica 1: Same rack as writer, local node when possible
- Replica 2: Different rack
- Replica 3: Same as Replica 2’s rack, different node

Goal: Balance reliability (rack-awareness) and write bandwidth.
Read Path (HDFS vs GFS):
  • Client asks NameNode for block locations.
  • Client then streams from the nearest DataNode (data path does not go through the NameNode).
  • For multi-block files, the client will pipeline across DataNodes in sequence.
Write Path:
  • Client requests a new block from NameNode.
  • NameNode chooses a replica pipeline (e.g., DN1 → DN2 → DN3).
  • Client writes to DN1, which streams the same bytes to DN2, which streams to DN3.
  • If any DataNode fails, the pipeline is reconfigured and the block is re-replicated later.

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Chapter 3: MapReduce Framework – Batch Processing at Scale

Problem: Let ordinary developers process terabytes of data on a cluster without managing threads, failures, or data distribution. Programming Model:
  • Map: Transform input records into intermediate (key, value) pairs.
  • Shuffle: Group all values by key across the cluster.
  • Reduce: Aggregate values for each key to produce final results.
MAPREDUCE DATA FLOW (LOGICAL)

Input Splits → map() → shuffle/sort → reduce() → Output
Execution Architecture (Classic MRv1):
  • JobTracker: Central coordinator; schedules tasks, tracks progress, handles retries.
  • TaskTrackers: Run map and reduce tasks inside fixed “slots”.
  • InputFormat / OutputFormat: Decide how to slice data into splits and how to write results.
Data Locality in Map Phase:
  • Each map task is ideally scheduled on a node that has the relevant HDFS block.
  • If not possible, scheduler falls back to same-rack or remote execution.
Shuffle and Sort:
  • Map tasks buffer intermediate key-value pairs, partition them by reducer, and spill to local disk.
  • A background thread merges and sorts these segments.
  • Reduce tasks pull data from multiple map outputs over the network, merge sort them, and feed sorted groups into the reduce() function.
SHUFFLE BOTTLENECKS

- Too many small map outputs → many tiny network transfers.
- Skewed keys → one reducer becomes a straggler.
- Solutions: combiner functions, custom partitioners, skew-aware partitioning.
Fault Tolerance:
  • If a map or reduce task fails, JobTracker re-schedules it on another TaskTracker.
  • Task outputs are immutable; re-running a task doesn’t corrupt others.
  • Completed task outputs are stored on local disk; if that disk fails, the task is recomputed from HDFS.

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Chapter 4: YARN – Decoupling Resource Management

MapReduce-as-the-only-workload became a limitation. YARN generalizes the cluster to run multiple processing engines. Key Ideas:
  • Separate resource management from application logic.
  • Support many frameworks (MapReduce v2, Tez, Spark, Flink) sharing the same cluster.
Core Components:
  • ResourceManager (RM): Global scheduler and resource arbitrator.
  • NodeManager (NM): Per-node agent reporting resource usage, launching containers.
  • ApplicationMaster (AM): Framework-specific orchestrator (one per application).
  • Containers: Resource bundles (CPU, memory, etc.) allocated to run tasks.
YARN CONTROL FLOW

1. Client → RM: "Start application X".
2. RM allocates first container → launches ApplicationMaster (AM).
3. AM negotiates with RM for more containers to run its tasks.
4. AM talks to NodeManagers to start/stop containers.
5. When done, AM unregisters from RM.
Scheduling Policies:
  • Capacity Scheduler: Multi-tenant, hierarchical queues with guaranteed capacities.
  • Fair Scheduler: Aims to give equal shares of the cluster to active users/jobs.
Why This Matters:
  • Enables mixed workloads: long-running services, interactive SQL, streaming, and batch.
  • Prevents one MapReduce job from monopolizing the cluster.

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Chapter 5: Hadoop Ecosystem – Beyond HDFS and MapReduce

Hadoop’s long-term impact comes from the ecosystem built on top of its storage and resource layers. Storage Models:
  • HDFS: Write-once, read-many file storage.
  • HBase: Random-access, sparse, column-family store (inspired by Bigtable).
  • Columnar formats (Parquet/ORC): Highly compressed, analytic-friendly layout.
Query Engines:
  • Hive: SQL over HDFS; rewrites queries into MapReduce/Tez/Spark jobs.
  • Impala / Presto / Trino: Low-latency, MPP-style query engines.
Processing Engines:
  • Original MapReduce: Disk-bound batch processing.
  • Tez: DAG-structured jobs with fewer materializations.
  • Spark: In-memory RDD/DataFrame abstractions; batch, streaming, ML.
Coordination & Workflow:
  • ZooKeeper: Coordination, leader election, configuration.
  • Oozie / Airflow: DAG-based workflow schedulers orchestrating many jobs.
  • Kafka: Durable event log feeding Hadoop-based batch and stream pipelines.
The chapter focuses less on “API usage” and more on how these systems compose into a coherent data platform and what invariants they rely on from HDFS and YARN.

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Chapter 6: Fault Tolerance – Designing for Constant Failure

At Hadoop scale, failure is continuous, not exceptional. HDFS Fault Tolerance:
  • Replication: Lose up to replicationFactor - 1 nodes without losing data.
  • Heartbeats & Block Reports: NameNode continuously monitors DataNode liveness.
  • Re-replication: On DataNode failure, blocks are automatically cloned to new nodes.
NameNode Resilience:
  • Edit log + fsimage: Write-ahead log of metadata mutations plus periodic snapshots.
  • Checkpointing: Merges edit log into fsimage to bound replay time.
  • HA Mode (HDFS 2.x+): Active and Standby NameNodes coordinated via ZooKeeper.
MapReduce / YARN Fault Tolerance:
  • Task retry: Failed tasks are re-run elsewhere; job fails only after exceeding retry limits.
  • Speculative execution: Duplicate slow tasks to mitigate stragglers.
  • AM recovery (YARN): In some setups, ApplicationMasters can be restarted and resume work.
The chapter reads like a reliability engineering document: it enumerates failure modes (disk loss, node loss, rack loss, network partitions, NameNode crashes) and shows concretely how Hadoop responds in each case.

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Chapter 7: Performance & Tuning – Pushing the Cluster to Its Limits

This chapter focuses on bottleneck analysis and tuning strategies. Where Time Goes in a Typical Job:
  • HDFS read/write throughput (disk + network).
  • Map-side parsing and serialization.
  • Shuffle (network + disk merges).
  • Reduce-side aggregation and output formatting.
Key Tuning Levers:
  • Data layout: Prefer columnar formats (Parquet/ORC) for analytical queries.
  • Compression: Use block-level compression (e.g., Snappy, LZO) to reduce I/O and network.
  • Parallelism: Tune number of mappers/reducers, container sizes, and YARN queue capacities.
  • Locality: Monitor locality rates; low locality often signals cluster imbalance.
EXAMPLE TRADE-OFF

- More reducers:
  + Fewer keys per reducer → less skew
  - More small output files and overhead

- Fewer reducers:
  + Larger outputs per reducer → fewer files
  - Risk of stragglers and hotspots
Cluster-Level Considerations:
  • Network topology (oversubscription ratios, rack layout).
  • Disk configuration (number of spindles per node, SSD caches).
  • Garbage collection tuning for long-lived JVM processes.

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Chapter 8: Production Deployment – From Lab to Data Platform

This chapter treats Hadoop as a product you operate, not a library you call. Cluster Design:
  • Node roles: Edge nodes vs masters vs workers.
  • High availability: Redundant masters, NameNode HA, multiple RMs (dependent on distro).
  • Security: Kerberos authentication, HDFS encryption zones, network ACLs.
Operational Playbooks:
  • Adding/removing nodes without downtime.
  • Rolling upgrades and configuration changes.
  • Handling NameNode failover events.
  • Capacity planning (storage growth vs compute demand).
Monitoring & Observability:
  • Metrics: HDFS capacity, block replication health, job latencies, YARN queue utilization.
  • Logs: Centralized log aggregation for HDFS, YARN, and ecosystem services.
  • Alerting: Threshold-based alerts for under-replicated blocks, full disks, failing nodes.
By the end of this chapter, Hadoop is framed the way SREs view any large-scale distributed system: in terms of SLIs/SLOs, failure modes, and runbooks.

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Key Design Principles

Core Hadoop Principles to Remember:
  1. Hardware Failure is Common → Detect and recover from failures automatically
  2. Moving Computation is Cheaper Than Moving Data → Data locality is key to performance
  3. Simple and Robust Beats Complex and Fragile → Prefer straightforward designs that work reliably
  4. Scale Out, Not Up → Add more machines rather than bigger machines
  5. Write Once, Read Many → Optimize for append-only workloads
  6. Portability Across Platforms → Run on commodity hardware with Linux
  7. Open Source and Community-Driven → Benefit from thousands of contributors worldwide

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What Makes This Course Different?

Complete Coverage

Covers HDFS, MapReduce, YARN, and ecosystem. Not just theory—real implementation details.

Interview Focused

36+ interview questions across all chapters. Practice explaining complex concepts clearly.

Visual Learning

Extensive diagrams showing data flows, architecture, and component interactions.

Production Insights

Real-world examples from Yahoo (created Hadoop), Facebook, LinkedIn, and others.

GFS Comparison

Understand how Hadoop implements and improves upon Google’s original designs.

Ecosystem Context

Learn how Hadoop fits into the broader big data landscape and modern alternatives.

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Expected Outcomes

After completing this course, you will be able to: 
TECHNICAL SKILLS:
────────────────
✓ Explain Hadoop architecture comprehensively
✓ Design HDFS storage strategies
✓ Write and optimize MapReduce jobs
✓ Understand YARN resource management
✓ Work with Hadoop ecosystem tools
✓ Compare Hadoop with alternatives (Spark, etc.)

INTERVIEW SKILLS:
────────────────
✓ Answer "How does Hadoop work?"
✓ Explain HDFS vs GFS differences
✓ Discuss MapReduce execution flow
✓ Analyze performance bottlenecks
✓ Compare distributed processing frameworks
✓ Design big data solutions

PRACTICAL SKILLS:
────────────────
✓ Deploy and configure Hadoop clusters
✓ Optimize job performance
✓ Troubleshoot common issues
✓ Plan capacity and resources
✓ Implement security and governance
✓ Choose appropriate ecosystem tools
Understanding Hadoop provides foundation for these systems:
Built on Hadoop:
  • Apache Hive: SQL query engine
  • Apache Pig: Data flow scripting
  • Apache HBase: NoSQL database
  • Apache Spark: In-memory processing
  • Apache Flink: Stream processing
  • Presto/Trino: Distributed SQL engine
These tools leverage HDFS and YARN infrastructure.

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Study Tips

Install Hadoop locally or use cloud sandbox environments. Running actual jobs solidifies understanding better than reading alone.
As you learn HDFS, constantly compare with GFS. Understanding differences deepens knowledge of both systems.
Sketch how data moves through MapReduce shuffle, HDFS replication, YARN scheduling. Visual understanding aids retention.
Hadoop is open source. Reading actual implementation provides insights no documentation can match.
Don’t skip questions. Practice explaining concepts aloud. Being able to teach demonstrates true understanding.

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Time Commitment

Full Deep Dive

14-18 hours
  • Read all chapters thoroughly
  • Work through all examples
  • Answer all interview questions
  • Experiment with Hadoop locally

Interview Prep Focus

8-10 hours
  • Focus on Chapters 1, 2, 3, 6
  • Practice interview questions
  • Understand core concepts
  • Compare with modern alternatives

Quick Overview

4-5 hours
  • Chapter 1: Origins
  • Chapter 2: HDFS basics
  • Chapter 3: MapReduce overview
  • Skim ecosystem chapters

Mastery Path

25+ hours
  • All chapters in depth
  • Install and configure cluster
  • Write sample MapReduce jobs
  • Explore ecosystem tools
  • Compare multiple systems

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Additional Resources

GFS Paper

“The Google File System” (2003) Foundation for HDFS design

MapReduce Paper

“MapReduce: Simplified Data Processing” (2004) Original programming model

Hadoop: The Definitive Guide

Tom White’s comprehensive book Industry-standard reference

Apache Hadoop Docs

Official documentation Latest features and APIs

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Get Started

Ready to master Apache Hadoop?

Start with Chapter 1

Begin your journey with Introduction & Origins to understand how Hadoop evolved from Google’s research papers.
Learning Strategy: Hadoop is a complex ecosystem. Take time to understand each component individually before seeing how they work together. The investment pays off in deep big data expertise.

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Course Map

START HERE
    ↓
┌─────────────────────────────────────────┐
│ Chapter 1: Introduction & Origins       │ ← Understand the history
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 2: HDFS Architecture            │ ← Learn the storage layer
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 3: MapReduce Framework          │ ← Master the processing model
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 4: YARN Resource Management     │ ← Understand orchestration
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 5: Hadoop Ecosystem             │ ← Explore the tools
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 6: Fault Tolerance              │ ← Handle failures
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 7: Performance & Tuning         │ ← Optimize performance
└─────────────────────────────────────────┘
    ↓
┌─────────────────────────────────────────┐
│ Chapter 8: Production Deployment        │ ← Deploy at scale
└─────────────────────────────────────────┘
    ↓
MASTER LEVEL: Comprehensive big data expertise

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How This Paper-Level Course Fits Into the Bigger Picture

This Hadoop “engineering paper” track is designed to complement more hands-on tooling courses.
  • If you’re reading this from the engineering-papers course: Treat it as your theoretical backbone—understand why Hadoop looks the way it does before you worry about commands.
  • If you’re also following the Hadoop tools modules (e.g., HDFS, MapReduce, YARN deep dives): Use this course to connect implementation details back to the original design goals and trade-offs.
  • If you’re coming from the GFS paper track: Continuously map concepts (Master → NameNode, Chunkserver → DataNode, record appends, relaxed consistency) and note where Hadoop intentionally diverged.
HOW TO STUDY EFFECTIVELY

1. Pick one path:
   - GFS paper → Hadoop paper → Hadoop tools
   - or Hadoop paper → GFS paper (for historical contrast)

2. For each major concept:
   - Read the design motivation here
   - Skim the corresponding research paper sections
   - Then see how it is implemented in Hadoop code/docs

3. As you progress:
   - Maintain a personal "concept map" of storage, compute, and scheduling
   - Note recurring patterns: replication, data locality, failure recovery
This structure is intentional: by the end of the Hadoop paper track, you should be able to read production postmortems, design reviews, and research papers about large-scale data systems with ease. Let’s begin the journey into the distributed computing framework that democratized big data!