6. Concurrency

Question 1

Lock-Based Protocols
1- ___ (X) mode
2- ___(S) mode

Answer 1

Exclusive

Shared

Question 2

Exclusive (X) mode

Data item can be both ___. X-lock is requested using lock-X instruction.

Answer 2

Read and written

Question 3

Shared (S) mode

Data item can only be ___. S-lock is requested using lock-S instruction.

Answer 3

Read

Question 4

Deadlock

Happens when at least two ___ want the lock of ___

Answer 4

Transactions

Each other

Question 5

Starvation

Transaction needs to rollback beacause other transactions are constantly getting the desired ___

Answer 5

Lock

Question 6

Two-Phase Locking Protocol
1- ___ phase - ___obtain / ___ release Locks
2- ___ phase - ___ Obtain / ___release Locks

Answer 6

Growing / Can, Can’t

Shrinking Can’t, Can

Question 7

Graph-Based Protocols

A lock can only be obtained if the ___ lock is already obtained by the ___ transaction. We can’t ___unlocked items

Answer 7

Parent
Same
Re-lock

Question 8

Deadlock prevention protocols
Ensure that the system does not enter into a ___ state. Some prevention strategies:
1- Require that the transaction locks ___ before executing
2- ___ all data items and only allow locking in that ___

Answer 8

Deadlock
Everything
Order

Question 9

Wait-die scheme
Order transactions ___ while younger transactions ___
Wound-wait
Older transactions force younger ones to ___
Younger transactions ___
Timeout-based
Wait for only a specified amount of time then is ___

Answer 9

Wait 
Rollback
Rollback
Wait
Rollback

Question 10

Deadlock Detection (Wait-for graph)
The system is in a deadlock state if and only if the wait-for graph has a \_\_\_.

Answer 10

Cycle

Question 11

Intention Lock Modes
1- ___ (IS) - ___ locks at lower levels of tree
2- ___ (IX) - ___ or ___ locks at lowers level of the tree
3- ___ (SIX) - a ___ lock, with the possibility of
having exclusive or shared locks at lower levels of the tree.

Answer 11

1- Intention-shared / Shared
2- Intention-exclusive / Exclusive or shared
3- Shared and intention-exclusive / Shared

Question 12

Multiple Granularity Locking Scheme
Before requesting IS or S lock, all ancestors nodes must be locked in ___
Before requesting IX, SIX or X lock, all ancestors nodes must be locked in ___
Leaf nodes are always locked in __, since they have no descendants
Locks are acquired in ___ oder
Locks are released during transaction in ___ order or at the end in ___ order
Cannot ___ locks

Answer 12

IS or IX
IX or SIX
S or X
Root-to-leaf
Leaf-to-root / any
Reacquire

Question 13

Timestamp Ordering
Read needs to take ___ time than largest ___ time saved, otherwise save new read time
Write needs to take ___ time than largest ___ and ___ time saved, otherwise save new ___ time

Answer 13

More
Write 
More 
Read and Write
Write

Question 14

Multiversion Timestamp Ordering

Equal to Timestamp ordering but we access version Qk that has the ___ W-Timestamp

Answer 14

Largest

Question 15

Snapshot Isolation

• Each transaction is given its own ___ of the database
• Updates are kept in the snapshot until the transaction ___
• Reqad Request never __ or ___

Answer 15

Snapshot
Commits
Wait or fail

Question 16

Validation Steps in Snapshot Isolation
1- ___ wins - first concurrent transaction to commit
2- ___ wins - first concurrent transaction to get the lock to the item

Answer 16

First Commiter

First Updater

Question 17

Serializable snapshot isolation (SSI)
A transaction is rolled back when it has both an incoming ___ conflict and an outgoing ___ conflict (almost like a cicle in theory)

Answer 17

read-write

read-write