Discuss different methods for concurrency control

Question 1

1. what is a locking method.

Answer 1

is placing locks on database objects (e.g. rows, tables) to prevent concurrent transactions from accessing or modifying the same data simultaneously.

Question 2

Lock granularity (level or lock use). - Database-Level lock

Answer 2

1. Database-level: restricts access to the owner of the lock and allows only one user at a time to access the database.

Question 3

Lock granularity (level or lock use). - Table-Level lock

Answer 3

2. Table-level: allows only one transaction at a time to access a table.
3. Page-level: an entire diskpage or section of a disk is locked.
4. Row-level: concurrent transaction

Question 4

Lock granularity (level or lock use). - Page-Level lock

Answer 4

3. Page-level: an entire diskpage or section of a disk is locked.

Question 5

Lock granularity (level or lock use). - Row-Level lock

Answer 5

4. Row-level: concurrent transactions to access the same rows of the same table, even if the rows are on the same page.

Question 6

Lock granularity (level or lock use). - Field-Level lock

Answer 6

5. Field-level: allows concurrent transactions to access the same rows as they require the use of different attributes within that row.

Question 7

Lock types - Binary Lock.

Answer 7

1. Binary lock - has only two states, locked (1) and unlocked (0). if a data item is locked, no other transaction can use that data item.

Question 8

Lock types - Exclusive lock.

Answer 8

Issued when a transactions must update or (WRITE) a data item, an exclusive lock is requested, its application for a lock will not proceed until all locks are released.

Question 9

Lock types - Shared lock.

Answer 9

multiple processes can simultaneously hold shared locks to enable them to read without updating.

Question 10

what is a deadlock

Answer 10

occurs when two transactions wait indefinitely for each other to unlock data.

Question 11

Deadlock Control Techniques. - Avoidance

Answer 11

Avoidance - transaction must obtain all the locks needed before it can be executed.

Question 12

Deadlock Control Techniques. - Prevention

Answer 12

Prevention - transaction requesting a new lock is aborted when there is a possibility that a deadlock can occur.

Question 13

Deadlock Control Techniques. - Detection

Answer 13

Detection - DBMS tests database periodically for deadblocks, if found, victim transaction is aborted.

Question 14

what is two-phase locking.

Answer 14

2PL - A set of rules that manage how transactions acquire and release locks to ensure serializability, though it doesnt prevent deadlocks.

Question 15

2PL - Growing Phase.

Answer 15

The transaction acquires all the locks it needs without releasing any.

Question 16

2PL - Shrinking Phase.

Answer 16

After reaching its locked point (where all necessary locks are obtained), the transaction releases its locks and cannot acquire new ones.

Question 17

2. What is timestamping

Answer 17

Time stamping: Assigns a global unique time stamp to each transaction.

Question 18

Time stamping properties - Uniqueness

Answer 18

Ensures no equal time stamp values exist

Question 19

Time stamping properties - Monotonicity

Answer 19

Ensures time stamp values always increased

Question 20

3. what is Optimistic methods

Answer 20

Optimistic approach: Assumes that most database operations do not conflict.