Concept explainers
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.
Row-level lock granularity:
This row-level locking process used to lock the single row in the table. It is used to improve the availability of data and involving in transaction conflict.
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Database Systems: Design, Implementation, & Management
- 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?arrow_forwardExplain 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_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
- In 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_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
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- Consider 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 ( picture bellow ) I want to get "T3 want to read all pages in F1 and modify about 10 pages, which can be identifiedonly after reading F1."arrow_forwardProvide a high-level intuition for why log records for transactions on the undo-list must be processed in reverse order, whereas redo is performed in a forward direction. What can go wrong if the undo-list is processed in a forward direction or redo is performed in a backward order?arrow_forwardSuppose you wish to create an audit trail of changes to the takes relation. Can the preceding implementation guarantee that updates made by a malicious database administrator (or someone who manages to get the administrator’s password) will be in the audit trail? Explain your answer.arrow_forward
- Database Systems: Design, Implementation, & Manag...Computer ScienceISBN:9781305627482Author:Carlos Coronel, Steven MorrisPublisher:Cengage LearningDatabase Systems: Design, Implementation, & Manag...Computer ScienceISBN:9781285196145Author:Steven, Steven Morris, Carlos Coronel, Carlos, Coronel, Carlos; Morris, Carlos Coronel and Steven Morris, Carlos Coronel; Steven Morris, Steven Morris; Carlos CoronelPublisher:Cengage Learning