INFO90002 Chap.8 Transactions, Concurrency and Recovery

Transactions, Concurrency and Recovery

Transactions, Concurrency and Recovery turns ACID properties, locking and isolation and logging and recovery into executable reasoning. The chapter's practical target is to trace an interleaving to the anomaly and isolation control, so every explanation should connect syntax to program state, control flow and observable output.

Treat ACID properties as a precise program object, not a loose label.

Identify its value or responsibility before execution, then trace what can read it, change it or depend on it. This makes hidden state changes visible before they become debugging guesses.

Use locking and isolation to explain the program's next move. Work through one representative input by hand and name the branch, iteration or call that follows.

If the trace cannot be stated, the code may run by accident rather than by understood design.

Bring in logging and recovery as the test of structure.

Compare normal, boundary and invalid inputs; state the expected behaviour first; then use the mismatch between expectation and result to localise the defect.

For the application — trace an interleaving to the anomaly and isolation control — write the smallest complete example that exposes the rule.

Explain why it works, what would break it and how the program should signal or recover from that failure.

Before running a Transactions, Concurrency and Recovery example, make a trace table with the important state before and after each operation. Include the value associated with ACID properties, the control decision governed by locking and isolation and the output or object affected by logging and recovery.

The table turns an unexplained result into a sequence that can be tested one transition at a time.

Test three inputs: an ordinary case, a boundary case and an invalid case. State the expected result for each before execution, then compare it with what the program actually does.

A useful test of locking and isolation isolates one rule; a test that changes several conditions at once cannot tell you which condition caused the failure.

Practise explaining the solution without reading the code.

For INFO90002, name the data representation, the control flow, the responsibility of each function or class and the reason the chosen design supports trace an interleaving to the anomaly and isolation control.

This rehearsal is especially important when a written test or interview asks why the program works rather than whether it produces one correct output.

A complete Transactions, Concurrency and Recovery response should make the task visible before the detail: identify what must be decided, define the relevant terms, connect the evidence to locking and isolation, and use logging and recovery to test the result.

The final sentence should answer the question actually asked rather than merely repeat the topic.

The controlling limit is specific: Serialisable behaviour can carry performance and deadlock costs.

Keep that limit beside the worked example, because it separates a careful INFO90002 answer from one that sounds confident but claims more than the task or evidence supports.

For revision, retrieve ACID properties, locking and isolation and logging and recovery without notes, explain their relationship aloud, then complete a changed version of the application: trace an interleaving to the anomaly and isolation control.

Record the first point at which your reasoning fails and repair that move before attempting another case.

What this chapter covers

• 01

  ACID properties

• 02

  locking and isolation

• 03

  logging and recovery

• 04

  Applying ACID properties

• 05

  Limits of locking and isolation and logging and recovery

Worked example: Transactions, Concurrency and Recovery

Key terms

transactions, concurrency and locking

A transaction is a logical unit of database work that should satisfy ACID properties; concurrency control and locking coordinate simultaneous transactions to prevent inconsistent or lost updates. In this chapter, use the concept when you trace an interleaving to the anomaly and isolation control.

referential integrity; logical vs physical data independence

Referential integrity requires each foreign key to match an existing referenced key or be null when allowed; logical and physical data independence protect users from changes to schemas or storage respectively. In this chapter, use the concept when you trace an interleaving to the anomaly and isolation control.

conceptual, logical and physical design (the database development lifecycle)

Conceptual design models business entities and relationships independently of technology, logical design translates them into a data model and constraints, and physical design specifies storage, indexes and implementation details. In this chapter, use the concept when you trace an interleaving to the anomaly and isolation control.

Transactions, Concurrency and Recovery FAQ

Exam move

Reconstruct the relationship among ACID properties, locking and isolation and logging and recovery; complete the chapter application without notes; then test the result against this limit: Serialisable behaviour can carry performance and deadlock costs.

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