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Questions and Answers
What describes a transaction in a DBMS?
What describes a transaction in a DBMS?
- A series of database schema modifications.
- A sequence of reads and writes to the database. (correct)
- The total number of operations in a DBMS.
- An isolated execution of a database program.
Which property ensures that transactions are treated as a single unit of work?
Which property ensures that transactions are treated as a single unit of work?
- Consistency
- Atomicity (correct)
- Isolation
- Durability
What is a serial schedule in transaction management?
What is a serial schedule in transaction management?
- A schedule that does not interleave the actions of different transactions. (correct)
- A schedule where only read operations are performed.
- A schedule that guarantees data integrity.
- A schedule that allows multiple transactions to run simultaneously.
What does a serializable schedule represent?
What does a serializable schedule represent?
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What happens if a transaction aborts in a DBMS?
What happens if a transaction aborts in a DBMS?
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Study Notes
Transactions Overview
- Concurrent execution of user programs enhances DBMS performance.
- A transaction acts as an abstract representation of a user's operations, focusing on database read/write activities.
Concurrency in DBMS
- Users perceive each transaction as executing independently.
- The DBMS manages concurrency by interleaving actions (reads and writes) of multiple transactions.
- Transactions must maintain database consistency, ensuring the database remains in a consistent state post-execution.
Atomicity of Transactions
- Transactions can either commit after all actions are executed or abort before completion.
- Atomicity is a critical property ensured by the DBMS, meaning that either all actions are completed, or none are applied.
- The DBMS logs transaction actions, enabling it to revert any changes made by aborted transactions.
Example of Transactions
- Two transactions example:
- T1: Increments A by 100 and decrements B by 100.
- T2: Multiplies A and B by 1.06.
- There is no guaranteed execution order between T1 and T2; however, their net effect must mirror the result of executing them sequentially.
Scheduling Transactions
- Serial Schedule: A type of scheduling where transaction actions do not intermingle.
- Equivalent Schedules: Two schedules are considered equivalent if executing them yields the same database state.
- Serializable Schedule: A schedule that can be rearranged to match the outcome of some serial execution of transactions.
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