quartz/content/BigData/RDBMS.md

Database Overview

What is an RDBMS?

Relational Database Management System:

• Data is stored in tables:

  • Rows = records
  • Columns = fields

• Each table has:

  • Indexes for fast searching
  • Relationships with other tables (via keys)

Relational model - Keys and Indexes

Ability to find record(s) quickly

• Operations become efficient:
  • Find by key → O(log n)
  • Fetch record by ID → O(1)

Indexes = sorted references to data locations → like a book index.

Relational model - Operations

Relational databases support CRUD:

• Create
• Read
• Update
• Delete

Each operation uses both:

• The index (to locate data)
• The data itself (to read/write)

Relational model - Transactional

Relational databases guarantee transaction safety with ACID:

• Atomicity – all or nothing
• Consistency – valid data only
• Isolation – no interference from other transactions
• Durability – survives crashes

• Examples:
  • Transferring money, Posting a tweet
  • Both must either succeed completely or fail completely.

Transactions guarantee data validity despite errors & failures

Relational model - SQL

SQL is the language used to talk to relational databases.

• Standard

• Query

• Language

• All RDBMSs use it (MySQL, PostgreSQL, Oracle, etc.)

 Pros and Cons of RDBMS

Pros:

• Structured data
• ACID transactions
• Powerful SQL
• Fast (for small/medium size)

Cons:

• Doesn’t scale well (single machine or SPOF = Single Point of Failure)
• Becomes slow with big data
• Less fault tolerant
• Not designed for massive, distributed systems