Suppose the deferred modification technique is used in a database. a. Is the old-value part of an update log record required any more? Why or why not? b. If old values are not stored in update log records, transaction undo. Is clearly not feasible. How would the redo-phase of recovery have to be modified as a result? C. Deferred modification can be implemented by keeping updated data items in local memory of transactions, and reading data items that have not been updated directly from the database buffer. Suggest how to efficiently implement a data item read, ensuring that a trans action sees its own updates.

Suppose the deferred modification technique is used in a database. a. Is the old-value part of an update log record required any more? Why or why not? b. If old values are not stored in update log records, transaction undo. Is clearly not feasible. How would the redo-phase of recovery have to be modified as a result? C. Deferred modification can be implemented by keeping updated data items in local memory of transactions, and reading data items that have not been updated directly from the database buffer. Suggest how to efficiently implement a data item read, ensuring that a trans action sees its own updates.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Suppose for a second that a technique known as snapshot isolation database is being used in order to provide security for the database of a financial institution.Do you have an example that explains how a nonserializable execution might be detrimental to the bank? If so, please share it with me. If so, please spread the word.
Suppose a transaction deletes a record, and the free space generated thus isallocated to a record inserted by another transaction, even before the first transaction commits.a. What problem can occur if the first transaction needs to be rolled back?b. Would this problem be an issue if page-level locking is used instead oftuple-level locking?c. Suggest how to solve this problem while supporting tuple-level locking,by logging post-commit actions in special log records, and executing them after commit. Make sure your scheme ensures that such actions are performed exactly once.
Imagine for a minute that a financial institution's database is safeguarded by a technique known as snapshot isolation database.Do you offer an example of how a nonserializable execution may be detrimental to the bank? Please share it if so.
Sometimes a transaction has to be undone after it has committed because it was erroneously executed—for example, because of erroneous input by a bank teller. a. Give an example to show that using the normal transaction undo mechanism to undo such a transaction could lead to an inconsistent state. b. One way to handle this situation is to bring the whole database to a state prior to the commit of the erroneous transaction (called point-in-time recovery). Transactions that committed later have their effects rolled back with this scheme. Suggest a modification to the recovery algorithm of Section 19.4 to implement point-in-time recovery using database dumps. c. Later nonerroneous transactions can be reexecuted logically, if the updates are available in the form of SQL but cannot be reexecuted using their log records. Why?
(2)How many safe sequences are there for the above snapshot? Briefly justify your answer. (3)If P1 requests an additional instance of each of A and C, that is, P1's request becomes (2, 4, 6), will this request result in a deadlock? If the answer is no, give a safe sequence. If the answer is yes, identify the processes that will be involved in the deadlock. Show your work.
Let's pretend for a second that a bank is using a technique called snapshot isolation database to safeguard its data.Is there a specific scenario in which a nonserializable execution would be bad for a bank? If you do, I'd appreciate it if you'd tell me about it.
Imagine for a minute that a financial institution's database is being safeguarded by the snapshot isolation database technique.Do you offer a concrete example of how a nonserializable execution may be detrimental to a bank? If so, please distribute it.
If you want to get the most out of this example, you should definitely begin by using a database that is "snapshot isolated" and is controlled by an airline. This will allow you to get the most out of this example. What if, rather than an operation that can be serialized, the improved overall performance of the airline was due to an execution that cannot be serialized?
Let's pretend a bank uses a technology called snapshot isolation to keep their database safe.Can you give an example of how the bank could be harmed by a nonserializable execution?
Imagine that a technique called snapshot isolation database is being used to keep a bank's database secure.Do you have an example that illustrates how a nonserializable execution might be detrimental to the bank?
Imagine for a moment that the database of a financial institution is being protected using a method known as snapshot isolation database.Do you have an example that demonstrates how a nonserializable execution might be harmful to the bank? If so, please share it.
This example might benefit from beginning with a database maintained by an airline that makes use of "snapshot isolation." What if, instead of producing a greater overall performance for the airline, a non-serializable execution did it instead?