Transactions, ACID & NoSQL

By the end, you can

• Explain what a database transaction is and why it is defined as all-or-nothing.
• Define each of the four ACID properties and give a one-sentence description of each.
• Identify dirty reads, non-repeatable reads, phantom reads, and lost updates and state which isolation level prevents each.
• Order the four standard isolation levels from weakest to strongest and state what each prevents.
• Contrast Two-Phase Locking and MVCC as concurrency-control strategies.
• Explain the Write-Ahead Log pattern and how it delivers both Atomicity and Durability.
• Name the four NoSQL families, give a canonical example database for each, and describe the workload each fits best.
• State the CAP theorem and explain the CP vs AP trade-off during a network partition.
• Distinguish ACID (strong, immediate consistency) from BASE (eventual consistency) and identify when each is appropriate.