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DBMS Korth Edition 4 Exercise 16 Question 31 (Page No. 636)
Give example schedules to show that if any of lookup, insert or delete do not lock the next key value, the phantom phenomenon could go undetected.
Give example schedules to show that if any of lookup, insert or delete do not lock the next key value, the phantom phenomenon could go undetected.
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DBMS Korth Edition 4 Exercise 16 Question 29 (Page No. 635)
Explain the reason for the use of degree-two consistency. What disadvantages dos this approach have ?
Explain the reason for the use of degree-two consistency. What disadvantages dos this approach have ?
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DBMS Korth Edition 4 Exercise 16 Question 28 (Page No. 635)
Devise a timestamp-based protocol that avoids the phantom phenomenon.
Devise a timestamp-based protocol that avoids the phantom phenomenon.
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DBMS Korth Edition 4 Exercise 16 Question 27 (Page No. 635)
Explain the phantom phenomenon. Why may this phenomenon lead to an incorrect concurrent execution despite the use of the two-phase locking protocol ?
Explain the phantom phenomenon. Why may this phenomenon lead to an incorrect concurrent execution despite the use of the two-phase locking protocol ?
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DBMS Korth Edition 4 Exercise 16 Question 26 (Page No. 635)
Consider the timestamp ordering protocol, and two transactions, one that writes two data items p and q, and another that reads the same two data items. Give a schedule whereby the timestamp test for a write operation fails and ... but are unable to complete their task because of interaction with the other processes, is called a live lock.)
Consider the timestamp ordering protocol, and two transactions, one that writes two data items p and q, and another that reads the same two data items. Give a schedule wh...
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DBMS Korth Edition 4 Exercise 16 Question 25 (Page No. 635)
If deadlock is avoided by deadlock avoidance schemes, is starvation still possible ? Explain your answer.
If deadlock is avoided by deadlock avoidance schemes, is starvation still possible ? Explain your answer.
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DBMS Korth Edition 4 Exercise 16 Question 24 (Page No. 635)
Under what conditions is it less expensive to avoid deadlock than to allow deadlocks to occur and then to detect them ?
Under what conditions is it less expensive to avoid deadlock than to allow deadlocks to occur and then to detect them ?
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DBMS Korth Edition 4 Exercise 16 Question 23 (Page No. 635)
Explain why the following technique for transaction execution may provide better performance than just using strict two-phase locking: First execute the transaction without acquiring any locks and without performing any writes to the database ... , rerun the transaction using strict two-phase locking. (Hint: Consider waits for disk I/O.)
Explain why the following technique for transaction execution may provide better performance than just using strict two-phase locking: First execute the transaction witho...
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DBMS Korth Edition 4 Exercise 16 Question 22 (Page No. 635)
Under a modified version of the timestamp protocol, we require that a commit bit be tested to see whether a read request must wait. Explain how the commit bit can prevent cascading abort. Why is this test not necessary for write requests?
Under a modified version of the timestamp protocol, we require that a commit bit be tested to see whether a read request must wait. Explain how the commit bit can prevent...
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DBMS Korth Edition 4 Exercise 16 Question 21 (Page No. 635)
For each of the following protocols, describe aspects of practical applications that would lead you to suggest using the protocol, and aspects that would suggest not using the protocol: $ $ Two-phase locking $ $ Two-phase ... $ $ Timestamp ordering $ $ Validation $ $ Multi version timestamp ordering $ $ Multi version two-phase locking
For each of the following protocols, describe aspects of practical applications that would lead you to suggest using the protocol, and aspects that would suggest not usin...
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DBMS Korth Edition 4 Exercise 16 Question 20 (Page No. 635)
Show that there are schedules that are possible under the two-phase locking protocol, but are not possible under the timestamp protocol, and vice versa.
Show that there are schedules that are possible under the two-phase locking protocol, but are not possible under the timestamp protocol, and vice versa.
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DBMS Korth Edition 4 Exercise 16 Question 18 (Page No. 634)
Use of multiple-granularity locking may require more or fewer locks than an equivalent system with a single lock granularity. Provide examples of both situations, and compare the relative amount of concurrency allowed.
Use of multiple-granularity locking may require more or fewer locks than an equivalent system with a single lock granularity. Provide examples of both situations, and com...
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DBMS Korth Edition 4 Exercise 16 Question 17 (Page No. 634)
Although SIX mode is useful in multiple-granularity locking, an exclusive and intend-shared (XIS) mode is of no use. Why is it useless ?
Although SIX mode is useful in multiple-granularity locking, an exclusive and intend-shared (XIS) mode is of no use. Why is it useless ?
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DBMS Korth Edition 4 Exercise 16 Question 16 (Page No. 634)
In multiple-granularity locking, what is the difference between implicit and explicit locking ?
In multiple-granularity locking, what is the difference between implicit and explicit locking ?
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DBMS Korth Edition 4 Exercise 16 Question 15 (Page No. 634)
When a transaction is rolled back under timestamp ordering, it is assigned a new timestamp. Why can it not simply keep its old timestamp ?
When a transaction is rolled back under timestamp ordering, it is assigned a new timestamp. Why can it not simply keep its old timestamp ?
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DBMS Korth Edition 4 Exercise 16 Question 14 (Page No. 634)
In timestamp ordering,$W-timestamp(Q)$ denotes the largest timestamp of any transaction that executed $write(Q)$ successfully. Suppose that, instead, we defined it to be the timestamp of the most recent transaction to execute $write(Q)$ successfully.Would this change in wording make any difference ? Explain your answer.
In timestamp ordering,$W-timestamp(Q)$ denotes the largest timestamp of any transaction that executed $write(Q)$ successfully. Suppose that, instead, we defined it to be ...
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DBMS Korth Edition 4 Exercise 16 Question 13 (Page No. 634)
Consider a database system that includes an atomic increment operation, in addition to the read and write operations. Let V be the value of data item X. The operation $increment(X)$ by C sets the value of ... of increment mode locks allows for increased concurrency. (Hint: Consider check-clearing transactions in our bank example.)
Consider a database system that includes an atomic increment operation, in addition to the read and write operations. Let V be the value of data item X. The operation $in...
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DBMS Korth Edition 4 Exercise 16 Question 12 (Page No. 633-634)
Locking is not done explicitly in persistent programming languages. Rather, objects (or the corresponding pages) must be locked when the objects are accessed. Most modern operating systems allow the user to set access ... how the access-protection mechanism can be used for page-level locking in a persistent programming language.
Locking is not done explicitly in persistent programming languages. Rather, objects (or the corresponding pages) must be locked when the objects are accessed. Most modern...
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DBMS Korth Edition 4 Exercise 16 Question 11 (Page No. 633)
Consider a variant of the tree protocol called the forest protocol. The database is organized as a forest of rooted trees. Each transaction $T_i$ must follow the following rules: $ $ The first lock in each tree may be on ... relocked by Ti after it has been unlocked by $T_i$. Show that the forest protocol does not ensure serializability.
Consider a variant of the tree protocol called the forest protocol. The database is organized as a forest of rooted trees. Each transaction $T_i$ must follow the followin...
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DBMS Korth Edition 4 Exercise 16 Question 10 (Page No. 633)
Consider the following graph-based locking protocol that allows only exclusive lock modes, and that operates on data graphs that are in the form of a rooted directed acyclic graph. $ $ A transaction can lock any vertex first ... a lock on one of the parents of the vertex. Show that the protocol ensures serializability and deadlock freedom.
Consider the following graph-based locking protocol that allows only exclusive lock modes, and that operates on data graphs that are in the form of a rooted directed acyc...
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DBMS Korth Edition 4 Exercise 16 Question 9 (Page No. 633)
Consider the following graph-based locking protocol, which allows only exclusive lock modes, and which operates on data graphs that are in the form of a rooted directed acyclic graph. $ $ A transaction can lock any ... lock on the majority of the parents of that vertex. Show that the protocol ensures serializability and deadlock freedom.
Consider the following graph-based locking protocol, which allows only exclusive lock modes, and which operates on data graphs that are in the form of a rooted directed a...
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DBMS Korth Edition 4 Exercise 16 Question 8 (Page No. 633)
Consider the following extension to the tree-locking protocol, which allows both shared and exclusive locks: $ $ A transaction can be either a read-only transaction, in which case it can request only shared locks, ... , whereas update transactions must lock the root first. Show that the protocol ensures serializability and deadlock freedom.
Consider the following extension to the tree-locking protocol, which allows both shared and exclusive locks:$•$ A transaction can be either a read-only transaction, in ...
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DBMS Korth Edition 4 Exercise 16 Question 7 (Page No. 633)
Show by example that there are schedules possible under the tree protocol that are not possible under the two-phase locking protocol, and vice versa.
Show by example that there are schedules possible under the tree protocol that are not possible under the two-phase locking protocol, and vice versa.
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DBMS Korth Edition 4 Exercise 16 Question 6 (Page No. 632)
Consider a database organized in the form of a rooted tree. Suppose that we insert a dummy vertex between each pair of vertices. Showthat, if we follow the tree protocol on the new tree, we get better concurrency than if we follow the tree protocol on the original tree.
Consider a database organized in the form of a rooted tree. Suppose that we insert a dummy vertex between each pair of vertices. Showthat, if we follow the tree protocol ...
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DBMS Korth Edition 4 Exercise 16 Question 5 (Page No. 632)
Most implementations of database systems use strict two-phase locking. Suggest three reasons for the popularity of this protocol.
Most implementations of database systems use strict two-phase locking. Suggest three reasons for the popularity of this protocol.
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DBMS Korth Edition 4 Exercise 16 Question 4 (Page No. 632)
What benefit does rigorous two-phase locking provide ? How does it compare with other forms of two-phase locking ?
What benefit does rigorous two-phase locking provide ? How does it compare with other forms of two-phase locking ?
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DBMS Korth Edition 4 Exercise 16 Question 3 (Page No. 632)
What benefit does strict two-phase locking provide ? What disadvantages result ?
What benefit does strict two-phase locking provide ? What disadvantages result ?
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DBMS Korth Edition 4 Exercise 16 Question 2 (Page No. 632)
Consider the following two transactions: $T_{31}$: $read(A);$ $read(B);$ $if A = 0$ $then$ $B := B + 1;$ $write(B);$ $T_{32}$: $read(B);$ $read(A);$ $if B = 0$ $then$ $A := A + 1;$ ... to transactions $T_{31}$ and $T_{32}$, so that they observe the two-phase locking protocol. Can the execution of these transactions result in a deadlock ?
Consider the following two transactions:$T_{31}$: $read(A);$ $read(B);$ $if A = 0$ $then$ $B := B + 1;$ $write(B);$$T_{32}$: $read(B);$ ...
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DBMS Korth Edition 4 Exercise 16 Question 1 (Page No. 632)
Show that the two-phase locking protocol ensures conflict serializability,and that transactions can be serialized according to their lock points.
Show that the two-phase locking protocol ensures conflict serializability,and that transactions can be serialized according to their lock points.
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DBMS Korth Edition 4 Exercise 15 Question 12 (Page No. 590)
What is a cascadeless schedule ? Why is cascadelessness of schedules desirable ? Are there any circumstances under which it would be desirable to allow noncascadeless schedules ? Explain your answer.
What is a cascadeless schedule ? Why is cascadelessness of schedules desirable ? Are there any circumstances under which it would be desirable to allow noncascadeless sch...
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