ACID Properties

(Information Science Expert) Lecture on Database

• Atomicity
  • Atomicity ensures that operations are either fully completed or not performed at all.
  • Without atomicity, various error cases can occur, making it difficult to handle.
• Consistency
  • Consistency ensures that data remains in a valid state after processing.
• Isolation
  • Isolation guarantees that concurrent execution produces the same result as serial execution.
  • It is important to avoid simultaneous access or updates to the same data.
  • How to achieve isolation:
    • It would be ideal to know if we are currently operating on the latest data.
      • ”Pessimistic Concurrency Control“:
        • Limit the latest version of the data to one (locking).
        • Although parallel execution is difficult, it is less likely to fail.
        • Suitable for cases where collisions are likely to occur.
      • ”Optimistic Concurrency Control“:
        • Record the timestamp of data access/update and check again when the transaction is finished to ensure that no one else has accessed it.
        • If someone else has accessed it, the transaction is aborted (failed).
          • (To ensure atomicity, everything is rolled back.)
        • Suitable for cases where collisions are less likely to occur.
    • Alternatively, there are also DBMSs that allow multiple versions of the latest edition, similar to git.
      • MVCC (Only limit the latest version during updates)
    • Comparison between git and traditional DBMS
      • DBMS: Independence in terms of ACID Properties
      • git
        • Allows multiple latest versions
        • Attempts automatic merging (manual merging if failed)
      • DBMS (Manages only a single edition)
        • Manual merging after failed merging? That’s not feasible.
        • Ensures independence through serializability.
• Durability
  • Ensures persistence even in the event of failures.