Database Management Systems · Transactions and concurrency

Transactions and ACID properties

The four guarantees (atomicity, consistency, isolation, durability) that make a transaction feel like one indivisible unit.

Also known as: ACID, atomicity consistency isolation durability.

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• Relational model: Data as tables of rows and columns, with no other structure implied.

Leads to

• Concurrency anomalies: The specific bad things that can happen when two transactions run at the same time: dirty, non-repeatable, and phantom reads.
• Write-ahead logging and recovery: Writing what you're about to change to a log before touching the actual page, so a crash can still recover the right state.
• Distributed databases: A database whose data lives across multiple machines instead of one.

Related topics

• Write-ahead logging and recovery: Writing what you're about to change to a log before touching the actual page, so a crash can still recover the right state.
• Concurrency anomalies: The specific bad things that can happen when two transactions run at the same time: dirty, non-repeatable, and phantom reads.
• Distributed databases: A database whose data lives across multiple machines instead of one.