Database System Concepts
7th Edition
ISBN: 9781260084504
Author: Abraham Silberschatz, S. Sudarshan, Abraham, Henry Korth, Silberschatz Abraham, Silberschatz Professor
Publisher: McGraw-Hill Education
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Expert Solution & Answer
Chapter 19, Problem 9PE
Explanation of Solution
a.
Problem occurred when rolling back first transaction:
- Consider the given case where another transaction takes up the space generated by the deletion of a record by an uncommitted transaction.
- In case, if the first transaction needs to be rolled back, then
- The record deleted by the first transaction is restored.
- When the usual physical manner undo is performed with the old record values;
- The space that was reallocated to the new record by the second transaction would get overwritten by this undo...
Explanation of Solution
b.
Issues:
- When page-level locking is used, this problem will not crop up because of the following reasons:
- The free space gener...
Explanation of Solution
c.
Solving the problem:
In order to resolve the problem using tuple-locking the following methods are followed:
- Defer the freeing up of space until a transaction commit.
- Here, ensure that the space will be freed even when a system fails just after the commit.
- For this, the log records are modified for including the information about the space being freed, which should have been performed after the commit.
- In fact, all such operations can be performed as a transaction along generating their log records, followed by the post-commit log records...
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