Database Systems: Design, Implementation, & Management
13th Edition
ISBN: 9781337627900
Author: Carlos Coronel, Steven Morris
Publisher: Cengage Learning
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Chapter 10, Problem 9P
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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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?
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?
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.
Chapter 10 Solutions
Database Systems: Design, Implementation, & Management
Ch. 10 - Prob. 1RQCh. 10 - Prob. 2RQCh. 10 - Prob. 3RQCh. 10 - Prob. 4RQCh. 10 - Prob. 5RQCh. 10 - Prob. 6RQCh. 10 - Prob. 7RQCh. 10 - Prob. 8RQCh. 10 - Prob. 9RQCh. 10 - Prob. 10RQ
Ch. 10 - Prob. 11RQCh. 10 - Prob. 12RQCh. 10 - Prob. 13RQCh. 10 - Prob. 14RQCh. 10 - Prob. 15RQCh. 10 - Prob. 16RQCh. 10 - Prob. 17RQCh. 10 - Prob. 1PCh. 10 - Prob. 2PCh. 10 - Prob. 3PCh. 10 - Prob. 4PCh. 10 - Prob. 5PCh. 10 - Prob. 6PCh. 10 - Prob. 7PCh. 10 - Prob. 8PCh. 10 - Prob. 9PCh. 10 - Prob. 10PCh. 10 - Prob. 11P
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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"?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_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_forward
- 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_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_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
- Explain the concept of conflict-avoidance and its application in concurrency control, with reference to techniques like Strict Two-Phase Locking and Serializable Snapshot Isolation.arrow_forwardConcurrency control is described as two transactions running at the same time that can enter the same database rows at different times. These simultaneous accesses are known as collisions, and if they are not treated properly, they may result in errors or inconsistency. “Overlapping is possible with higher concurrency”. Discover how concurrency control resolves overlapping in more detail.arrow_forwardIn the 2PL algorithm we considered, a transaction can't start until it has acquired all the locks it needs (we call this, Conservative 2PL). There is a different scheme possible, where a transaction does NOT need to wait for all its locks - it can start its transactions before all the locks have been acquired. What would be good about such a scheme, and, what would be bad? Do feel free to illustrate with a diagram.arrow_forward
- Explain the concept of serializability in the context of concurrency control. How is it different from other forms of consistency, such as linearizability or strict two-phase locking?arrow_forwardConsider 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 X to V + C in an atomic step. The value of X is not available to the transaction unless the latter executes a read(X).Assume that increment operations lock the item in increment mode using the compatibility matrix in Figure 18.25.a. Show that, if all transactions lock the data that they access in the corresponding mode, then two-phase locking ensures serializability.b. Show that the inclusion of increment mode locks allows for increasedconcurrency.arrow_forwardQuestion 1: True or False Question Answer We need transactions management for system effectiveness. In an E/R diagram, the relations cannot have their own keys. In a database system, we use write-ahead logging to achieve concurrency. We should avoid interleaving transactions. A schedule with Write-Write conflicts cannot be converted to a serial schedule. In strict 2PL, the program cannot access to the data when there is a lock on it. We prefer RAM than Disk since it is durable. The external merge sort algorithm can be complete with as little as two buffer pages.arrow_forward
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