Anna University DATABASE MANAGEMENT SYSTEMS Two marks for unit 4
PART A
1. What is transaction?
Collections of operations that form a single logical unit of work are called
transactions.
2. What are the two statements regarding transaction?
The two statements regarding transaction of the form:
.Begin transaction
.End transaction
3. What are the properties of transaction?
The properties of transactions are:
.Atomicity
.Consistency
.Isolation
.Durability
4. What is recovery management component?
Ensuring durability is the responsibility of a software component of the base
system called the recovery management component.
5. When is a transaction rolled back?
Any changes that the aborted transaction made to the database must be undone.
Once the changes caused by an aborted transaction have been undone, then the
transaction has been rolled back.
6. What are the states of transaction?
The states of transaction are
. Active
. Partially committed
. Failed
. Aborted
.Committed
.Terminated
7. What is a shadow copy scheme?
It is simple, but efficient, scheme called the shadow copy schemes. It is based on
making copies of the database called shadow copies that one transaction is active at a
time. The scheme also assumes that the database is simply a file on disk.
8. Give the reasons for allowing concurrency?
The reasons for allowing concurrency is if the transactions run serially, a short
transaction may have to wait for a preceding long transaction to complete, which can lead
to unpredictable delays in running a transaction.
So concurrent execution reduces the unpredictable delays in running transactions.
9. What is average response time?
The average response time is that the average time for a transaction to be
completed after it has been submitted.
10. What are the two types of serializability?
The two types of serializability is
. Conflict serializability
. View serializability
11. Define lock?
Lock is the most common used to implement the requirement is to allow a
transaction to access a data item only if it is currently holding a lock on that item.
12. What are the different modes of lock?
The modes of lock are:
.Shared
.Exclusive
13. Define deadlock?
Neither of the transaction can ever proceed with its normal execution. This
situation is called deadlock.
14. Define the phases of two phase locking protocol
. Growing phase: a transaction may obtain locks but not release any lock.
.Shrinking phase: a transaction may release locks but may not obtain any new
locks.
15. Define upgrade and downgrade?
It provides a mechanism for conversion from shared lock to exclusive lock is
known as upgrade.
It provides a mechanism for conversion from exclusive lock to shared lock is
known as downgrade.
16. What is a database graph?
The partial ordering implies that the set D may now be viewed as a directed
acyclic graph, called a database graph.
17. What are the two methods for dealing deadlock problem?
The two methods for dealing deadlock problem is deadlock detection and
deadlock recovery.
18. What is a recovery scheme?
An integral part of a database system is a recovery scheme that can restore the
database to the consistent state that existed before the failure.
19. What are the two types of errors?
The two types of errors are:
. Logical error
. System error
20. What are the storage types?
The storage types are:
. Volatile storage
. Nonvolatile storage
21. Define blocks?
The database system resides permanently on nonvolatile storage, and is
partitioned into fixed-length storage units called blocks.
22. What is meant by Physical blocks?
The input and output operations are done in block units. The blocks residing on
the disk are referred to as physical blocks.
23. What is meant by buffer blocks?
The blocks residing temporarily in main memory are referred to as buffer blocks.
24. What is meant by disk buffer?
The area of memory where blocks reside temporarily is called the disk buffer.
25. What is meant by log-based recovery?
The most widely used structures for recording database modifications is the log.
The log is a sequence of log records, recording all the update activities in the database.
There are several types of log records.
26. What are uncommitted modifications?
The immediate-modification technique allows database modifications to be output
to the database while the transaction is still in the active state. Data modifications written
by active transactions are called uncommitted modifications.
27. Define shadow paging.
An alternative to log-based crash recovery technique is shadow paging. This
technique needs fewer disk accesses than do the log-based methods.
28. Define page.
The database is partitioned into some number of fixed-length blocks, which are
referred to as pages.
29. Explain current page table and shadow page table.
The key idea behind the shadow paging technique is to maintain two page tables
during the life of the transaction: the current page table and the shadow page table. Both
the page tables are identical when the transaction starts. The current page table may be
changed when a transaction performs a write operation.
30. What are the drawbacks of shadow-paging technique?
•Commit Overhead
•Data fragmentation
•Garbage collection
30. Define garbage collection.
Garbage may be created also as a side effect of crashes. Periodically, it is
necessary to find all the garbage pages and to add them to the list of free pages. This
process is called garbage collection.
32. Differentiate strict two phase locking protocol and rigorous two phase locking
protocol.
In strict two phase locking protocol all exclusive mode locks taken by a
transaction is held until that transaction commits. Rigorous two phase locking protocol requires that all locks be held until the transaction commits.
33. How the time stamps are implemented
•Use the value of the system clock as the time stamp. That is a transaction’s
time stamp is equal to the value of the clock when the transaction enters the
system.
•Use a logical counter that is incremented after a new timestamp has been
assigned; that is the time stamp is equal to the value of the counter.
34. What are the time stamps associated with each data item?
• W-timestamp (Q) denotes the largest time stamp if any transaction that
executed WRITE (Q) successfully.
• R-timestamp (Q) denotes the largest time stamp if any transaction that
executed READ (Q) successfully.
1. Why is concurrency control needed? Explain lost update, Inconsistent retrievals and uncommitted dependency anomalies.
2. What is a deadlock ? How can a deadlock occur ? explain.
3. Briefly explain one deadlock prevention algorithm.
4. What if time stamping is used ? Explain briefly
5. What is two-phase locking and how does it guarantee serializability ?
6. Discuss the concurrency control mechanism in detail using suitable example.
7. Differentiate between Two phase locking and Rigorous two-phase locking.
8. How can deadlocks be avoided when using 2PL?
9. How Share and exclusive locks differ ?Explain.
10. How precedence graph can be used to detect deadlock ?
11. What is a system log ? What is the purpose of the system log in system recovery
12. Explain serializability
13. Explain lock based protocols
14. Explain two phase locking in detail.
15. Explain log based recovery in detail
16.Explain ACID properties
17.Discuss about recovery
PART A
1. What is transaction?
Collections of operations that form a single logical unit of work are called
transactions.
2. What are the two statements regarding transaction?
The two statements regarding transaction of the form:
.Begin transaction
.End transaction
3. What are the properties of transaction?
The properties of transactions are:
.Atomicity
.Consistency
.Isolation
.Durability
4. What is recovery management component?
Ensuring durability is the responsibility of a software component of the base
system called the recovery management component.
5. When is a transaction rolled back?
Any changes that the aborted transaction made to the database must be undone.
Once the changes caused by an aborted transaction have been undone, then the
transaction has been rolled back.
6. What are the states of transaction?
The states of transaction are
. Active
. Partially committed
. Failed
. Aborted
.Committed
.Terminated
7. What is a shadow copy scheme?
It is simple, but efficient, scheme called the shadow copy schemes. It is based on
making copies of the database called shadow copies that one transaction is active at a
time. The scheme also assumes that the database is simply a file on disk.
8. Give the reasons for allowing concurrency?
The reasons for allowing concurrency is if the transactions run serially, a short
transaction may have to wait for a preceding long transaction to complete, which can lead
to unpredictable delays in running a transaction.
So concurrent execution reduces the unpredictable delays in running transactions.
9. What is average response time?
The average response time is that the average time for a transaction to be
completed after it has been submitted.
10. What are the two types of serializability?
The two types of serializability is
. Conflict serializability
. View serializability
11. Define lock?
Lock is the most common used to implement the requirement is to allow a
transaction to access a data item only if it is currently holding a lock on that item.
12. What are the different modes of lock?
The modes of lock are:
.Shared
.Exclusive
13. Define deadlock?
Neither of the transaction can ever proceed with its normal execution. This
situation is called deadlock.
14. Define the phases of two phase locking protocol
. Growing phase: a transaction may obtain locks but not release any lock.
.Shrinking phase: a transaction may release locks but may not obtain any new
locks.
15. Define upgrade and downgrade?
It provides a mechanism for conversion from shared lock to exclusive lock is
known as upgrade.
It provides a mechanism for conversion from exclusive lock to shared lock is
known as downgrade.
16. What is a database graph?
The partial ordering implies that the set D may now be viewed as a directed
acyclic graph, called a database graph.
17. What are the two methods for dealing deadlock problem?
The two methods for dealing deadlock problem is deadlock detection and
deadlock recovery.
18. What is a recovery scheme?
An integral part of a database system is a recovery scheme that can restore the
database to the consistent state that existed before the failure.
19. What are the two types of errors?
The two types of errors are:
. Logical error
. System error
20. What are the storage types?
The storage types are:
. Volatile storage
. Nonvolatile storage
21. Define blocks?
The database system resides permanently on nonvolatile storage, and is
partitioned into fixed-length storage units called blocks.
22. What is meant by Physical blocks?
The input and output operations are done in block units. The blocks residing on
the disk are referred to as physical blocks.
23. What is meant by buffer blocks?
The blocks residing temporarily in main memory are referred to as buffer blocks.
24. What is meant by disk buffer?
The area of memory where blocks reside temporarily is called the disk buffer.
25. What is meant by log-based recovery?
The most widely used structures for recording database modifications is the log.
The log is a sequence of log records, recording all the update activities in the database.
There are several types of log records.
26. What are uncommitted modifications?
The immediate-modification technique allows database modifications to be output
to the database while the transaction is still in the active state. Data modifications written
by active transactions are called uncommitted modifications.
27. Define shadow paging.
An alternative to log-based crash recovery technique is shadow paging. This
technique needs fewer disk accesses than do the log-based methods.
28. Define page.
The database is partitioned into some number of fixed-length blocks, which are
referred to as pages.
29. Explain current page table and shadow page table.
The key idea behind the shadow paging technique is to maintain two page tables
during the life of the transaction: the current page table and the shadow page table. Both
the page tables are identical when the transaction starts. The current page table may be
changed when a transaction performs a write operation.
30. What are the drawbacks of shadow-paging technique?
•Commit Overhead
•Data fragmentation
•Garbage collection
30. Define garbage collection.
Garbage may be created also as a side effect of crashes. Periodically, it is
necessary to find all the garbage pages and to add them to the list of free pages. This
process is called garbage collection.
32. Differentiate strict two phase locking protocol and rigorous two phase locking
protocol.
In strict two phase locking protocol all exclusive mode locks taken by a
transaction is held until that transaction commits. Rigorous two phase locking protocol requires that all locks be held until the transaction commits.
33. How the time stamps are implemented
•Use the value of the system clock as the time stamp. That is a transaction’s
time stamp is equal to the value of the clock when the transaction enters the
system.
•Use a logical counter that is incremented after a new timestamp has been
assigned; that is the time stamp is equal to the value of the counter.
34. What are the time stamps associated with each data item?
• W-timestamp (Q) denotes the largest time stamp if any transaction that
executed WRITE (Q) successfully.
• R-timestamp (Q) denotes the largest time stamp if any transaction that
executed READ (Q) successfully.
PART B
1. Why is concurrency control needed? Explain lost update, Inconsistent retrievals and uncommitted dependency anomalies.
2. What is a deadlock ? How can a deadlock occur ? explain.
3. Briefly explain one deadlock prevention algorithm.
4. What if time stamping is used ? Explain briefly
5. What is two-phase locking and how does it guarantee serializability ?
6. Discuss the concurrency control mechanism in detail using suitable example.
7. Differentiate between Two phase locking and Rigorous two-phase locking.
8. How can deadlocks be avoided when using 2PL?
9. How Share and exclusive locks differ ?Explain.
10. How precedence graph can be used to detect deadlock ?
11. What is a system log ? What is the purpose of the system log in system recovery
12. Explain serializability
13. Explain lock based protocols
14. Explain two phase locking in detail.
15. Explain log based recovery in detail
16.Explain ACID properties
17.Discuss about recovery
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