Suppose a transaction deletes a record, and the free space generated thus is allocated 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 of tuple-level locking?

Suppose a transaction deletes a record, and the free space generated thus is allocated 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 of tuple-level locking?

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

See similar textbooks

Similar questions

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.
Consider a database belonging to an airline that employs the technique known as "snapshot isolation," for instance. In the event that the overall performance of the airline is improved, it may be acceptable to tolerate executions that cannot be serialised.
IHR Số? In your example scenaric 1) (Suppose that the database system is using the log-based recovery mechanism) What will be the corresponding output log records for the set of transactions shown below? Transaction T1 Transaction T2 Transaction T3 RI(A) WI(A) R2(B) R3(B) RI(B) WI(B) W2(AY W3(C) Commit Conmit Abort [R=Read Operation; W: Write Operation: Assume any arbitrary value for Read-Write Operations]
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 isclearly not feasible. How would the redo phase of recovery have to bemodified as a result?c. Deferred modification can be implemented by keeping updated dataitems in local memory of transactions and reading data items that havenot been updated directly from the database buffer. Suggest how to efficientlyimplement a data item read, ensuring that a transaction sees itsown updates.d. What problem would arise with the above technique if transactions performa large number of updates?
131. In concurrency control policy the the lock is obtained on a. Entire database b. A particular transaction alone c. All the new elements d. All of the mentioned
Consider a file of 16384 records. Each record is 32 bytes long and its key field is of size 6 bytes. The file is ordered on a non-key field, and the file organization is unspanned. The file is stored in a file system with block size 1024 bytes, and the size of a block pointer is 10 bytes. If the secondary index is built on the key field of the file, and a multilevel index scheme is used to store the secondary index, the number of first-level and second-level blocks in the multilevel index are respectively
As an example, think of a database for an airline that uses something called "snapshot isolation." If the overall performance of the airline can be improved, it's possible that non-serializable executions might be acceptable.
Q1. Suppose a transaction T accesses (for read or write operations), a certain set of objects {O1,...,Ok}. This is done in the following manner: Step 1. T acquires exclusive locks to O1, . . . , Ok in increasing order of their addresses. Step 2. The required operations are performed. Step 3. All locks are released. Which Concurrency control protocol will be suitable for the given scenario, justify the answer will schedule as an example
Consider a database with objects X and Y. There are two transactions, as follows: T1: read(X), write(Y), write(X), commit T2: read(Y), write(X), write(Y), commit Give an example schedule that results in a Read-Write (RW) conflict. Explain why Strict Two-Phase Locking (Strict 2PL) would not allow your schedule from part (a) above. Give an example schedule that results in a Write-Write (WW) conflict. Explain why Strict Two-Phase Locking (Strict 2PL) would not allow your schedule from part (c) above.
Computer Science "For mutual exclusion with a preemptive scheduler, it is necessary to introduce explicit locks, and machinery that makes requesting processes wait when a lock is unavailable. We considered casting our locks as semaphores, but decided that, compared with monitors, they exert too little structuring discipline on concurrent programs." How do semaphores "exert too little structuring discipline" and how is this remedied by monitors? Construct an example to show how the structuring discipline exerted by monitors could be useful..
Explain why log records for undo-list transactions must be handled in reverse order, but redo is executed in a forward way.
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?