Database Systems: Design, Implementation, & Management
13th Edition
ISBN: 9781337627900
Author: Carlos Coronel, Steven Morris
Publisher: Cengage Learning
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Chapter 10, Problem 8P
Program Plan Intro
Pessimistic locking:
It is one of the locking methods in concurrency control. The lock exists in the transaction until the transaction gets committed or rolled back.
Two-phase locking protocol:
It defined the serializability of the transaction but not prevent deadlocks. The process of locking and unlocking can be done using two phases in this protocol. They are: Growing phase and shrinking phase.
Growing phase:
New lock can be occurred on the transaction without unlocking the data items. The data items are locked in this phase.
Shrinking phase:
This phase used to release all transaction but not provide new lock on the transaction.
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What does it mean for a database to be in a stable state? While the database management system may give a symbolic meaning for a transaction, there is no assurance that it faithfully captures the underlying real-world event. What consequences may be expected if this ban were implemented? Explain your point using an illustration. Should we take at face value the apparent meaning of the phrase "serializable transactions"?
Is a stable database state possible, and if so, how can it be achieved? There is no guarantee that the transaction's symbolic meaning accurately captures the underlying real-world event, and this is where the DBMS fails. Exactly what are the ramifications of such a ban? Give an illustration of what you mean. Does the term "serializable transactions" really mean what it appears to?
Transaction management deals with the problems of always keeping the database in a consistent state even when concurrent accesses and failures occur. Isolation requires that each transaction sees a consistent database at all times and that an executing transaction cannot reveal its results to other concurrent transactions before its commitment.
ANSWER
If two concurrent transactions access a data item that is being updated by one of them, it is not possible to guarantee that the second will read the correct value. Dirty reads and nonrepeatable reads may occur when one transaction can see intermediate results of another transaction before it has been committed.. Given below are two concurrent transactions T1 and T2 whose balances of amount x
(balx) were recorded at times t, between t₁ and tg. As shown in the table below:
If these two transactions interfere with each other, fill in the table below by selecting from the drop down list the values of balance X (bal,) at specified times…
Chapter 10 Solutions
Database Systems: Design, Implementation, & Management
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- When the application of an optimistic approach to concurrency control is implemented, it is frequently observed that transactions experience prolonged durations for completion. Explain?arrow_forwardIn a database transaction, the two main operations are READ and WRITE operations. So, there is a need to manage these two operations in the concurrent execution of the transactions as if these operations are not performed in an interleaved manner, and the data may become inconsistent. Consider the following scheduled transactions T1, T2, T3, and T4. T1 T2 T3 T4 Reads(X) Writes(X) Reads(Y) Writes(Y) Commit Reads(X) Time Reads(X) Writes(X) Reads(Y) Rollback Writes(Y) Writes(X) Commit • Identify all pair of transactions based on the occurred problem between two transactions (specify pairs, e.g., T1 => T2; T3=> T2; T3 =>T4; etc.). • Specify the name of a problem for each detected pair of transactions. • Justify the occurred problem for each pair of transactions.arrow_forwardSuppose 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?arrow_forward
- What does it mean for a database to be in a stable state? The database management system does not ensure that the transaction's symbolic meaning appropriately reflects the underlying real-world event. What would be the repercussions of such a ban? Using a concrete illustration, clarify your meaning. Does the word "serializable transactions" imply what it seems to mean?arrow_forwardConsider a multi-granularity locking system, with lock modes S, X, IS, IX, and SIX as in lecture and database-level, file-level, page-level and record-level locking as shown in the following figure. Provide the sequence of lock requests required to perform the following transactions and write necessary complete Lock and Unlock operations in their correct order. T3 want to read all pages in F1 and modify about 10 pages, which can be identified only after reading F1.(MY ANSWER) Lock-SIX(DB); Lock-S(F1); Lock-X(P1); Lock-X(P1000); Unlock(P1000); Unlock(P1); Unlock(F1); Unlock(DB); is it corect? ………………………………………………………………………………………arrow_forwardDifferentiate strict two phase locking protocol and rigorous two phase locking protocol.arrow_forward
- 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.arrow_forwardWhat is a stable database state, and how is it achieved?The DBMS gives no guarantee that the symbolic notion of the transaction appropriately matches the underlying real-world event.What are the possible consequences of the restriction? Please provide an example. What exactly is meant by "serializable transactions"?arrow_forwardA trigger's execution might result in the execution of another action. The depth of nesting in most database systems has a limit. Explain why they would put such a restriction in place.arrow_forward
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