ervijay
I have doubt in this question: In concurrency control, phantom problem may occur, when- a) records are inserted b) records are deleted c) records are modified d) records are indexed
Phantom problem concurrency control mein tab hota hai jab new records insert hote hain. Matlab ek transaction ne ek query chalayi aur uske baad doosri transaction ne naye records insert kar diye jo pehle result set mein nahi the, to next time woh query alag result degi. 👉 Correct answer: a) records are inserted”
But sir in the DBMS notes Delete wala example diya hua hai.. In notes only a diagram is given in which, Transaction T1 is Read(A) another Transaction T2 Delete(A), then T1 again Read(A)... That is what created doubt in my mind...
In concurrency control, the phantom problem occurs when records are inserted into the database during the execution of a transaction.
A) records are inserted
KG AI MentorKG AI Mentor
The phantom problem in concurrency control occurs when a transaction retrieves a set of rows based on a condition, and another transaction inserts new rows that satisfy the same condition, making the first transaction see "phantom" rows it didn't see before. Let’s analyze the options: a) records are inserted ✅ This is correct. The phantom problem specifically arises when new records are inserted that match the search condition of a transaction. For example, if Transaction A reads all employees in department 10, and Transaction B inserts a new employee in department 10, Transaction A may see a different result on a re-read — this is the phantom problem. b) records are deleted While deletions can affect the result set, they don’t cause the phantom problem per se. The issue is about new rows appearing, not disappearing. So this is not the best answer. c) records are modified Modifying existing records (e.g., changing a value) doesn’t create new rows, so it doesn’t cause the phantom problem. This is incorrect. d) records are indexed Indexing is a database optimization technique and not an operation that causes concurrency issues like the phantom problem. This is irrelevant. ✅ Correct Answer: a) records are insertedThe phantom problem is specifically related to insertions that create new rows matching a query condition, leading to inconsistent results across transactions. — KG AI Mentor 🤖
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