Session 3 : Transaction Management

Question 1

What is a Transaction?

Answer 1

A sequence of information exchanges and related actions,
such as database updates, deletions, modifications, or insertions.

Question 2

Consistent State of Database?

Answer 2

• A successful transaction moves the database from one consistent state to another.
• During execution, the database may be in an inconsistent state until the transaction is fully processed.
• Transaction is considetered completed only when it is either fully commited or entirely aborded.

Question 3

Database Request?

Answer 3

A database request refers to a single SQL statement executed within a transaction.

• If a transacrion consists of two UPDATE statements and one INSERT statement, it includes three database requests.

Question 4

Single-user vs Multi-user systems.

Answer 4

Single : most one user can use the system at a time.
Multi : many users can use the system concurrently.

Question 5

Single-processor vs Multi-processor computer system

Answer 5

Single-processor :
* Transactions execute sequentially.
* Which may lead to slower perforamnce

Multi-processor :
* Capable of parallel processing. (Interleaving)
* High performance can be expected

Question 6

Interleaving ?

Answer 6

• Allows the DBMS to switch between operation of different transactions.
• Concurrency in database is achieved through the interleaving, where multipe transactions are executed seemingly at the same time.

Question 7

4 important properties of transactions which DBMS must have?

Answer 7

ACID

1. Atomicity
2. Consistency
3. Isolation
4. Durability

• Atomicity : A transaction in DBMS is either completely executed or not executed at all.
• Consistency : Ensures the database remains in a vlid state. If consistency rules are violated, the transaction is rolled back, restoring the database to its original consistent state.
• Isolation : Transactions are executed independently of one another. Data in use during a transaction is inaccessible to another transaction until the transaction is complete.
• Durability : Committed data is permanently stored in the database. Once a transaction commits, its results are guaranteed to presist, even in case of system failures.

Question 8

Serializability in DBMS?

Answer 8

Ensures that concurrent transactions produce a consistent database state.

Question 9

Transaction states?

Answer 9

• BEGIN_TRANSACTION: marks start of transaction.
• READ OR WRITE: two possible operations on the data
• END_TRANSACTION: end of transaction process
• COMMIT_TRANSACTION: if no errors occur, save all changes to the database and mark transaction as complete.
• ROLLBACK OR ABORT: signals unsuccessful end of transaction, change applied to DB must be done.

Question 10

Transaction Log?

Answer 10

A history of all transactions executed by a database system.

Question 11

Transaction log content?

Answer 11

1. transaction id
2. for each transaction component:
   * Type of operation
   * Table name
   * before and after values
   * pointers
3. Transacion end