Database Systems: Design Implementation & Management
11th Edition
ISBN: 9781305850378
Author: Coronel
Publisher: Cengage
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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"?
An answer to this question: What does it mean to have a stable database state? There is no guarantee that the transaction's symbolic meaning accurately represents the underlying real-world event provided by the database management system. What would be the ramifications of such a prohibition? Using a specific example, explain what you mean. Does the term "serializable transactions" really mean what it appears to?
What does it mean to have a stable database state? There is no assurance that the symbolic meaning of the transaction adequately captures the underlying real-world event as given by the database management system. What would the consequences of such a restriction be? Explain what you mean with a particular example. Is it true that the word "serializable transactions" means what it seems to mean?
Chapter 10 Solutions
Database Systems: Design Implementation & Management
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- What does it mean for a database to have a stable state? There is no guarantee that the transaction's symbolic meaning accurately represents the underlying real-world event as provided by the database management system. What would be the effects of this restriction? Give a specific illustration of what you mean. Does the term "serializable transactions" really imply what it seems to mean?arrow_forwardTransaction 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…arrow_forwardWhen the application of an optimistic approach to concurrency control is implemented, it is frequently observed that transactions experience prolonged durations for completion. Explain?arrow_forward
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- When it comes to locking at several levels of granularity, what precisely differentiates implicit locking from explicit locking?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_forwardCan you define a database's stable state? The symbolic significance of the transaction may differ from its actual occurrence in the database management system. To what extent would a prohibition be felt? Give an instance to illustrate your point. Is there really anything to "serializable transactions"?arrow_forward
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