In concurrency control, phantom problem may occur, when-

The correct answer is records are inserted.

Key Points

• In concurrency control, the phantom problem occurs when records are inserted into the database during the execution of a transaction.
  • The phantom problem arises in a situation where a transaction reads a set of records that satisfy a certain condition, and another transaction inserts new records that also satisfy the same condition.
  • For example, if Transaction A reads all records where the age is greater than 30, and Transaction B inserts a new record with age 35, Transaction A may miss this new record if it reads again.
  • This leads to inconsistency because Transaction A's subsequent read operations may return a different set of records.
  • To prevent the phantom problem, isolation levels like Serializable are used, which ensures that no new records can be inserted that satisfy the condition during the transaction execution.

Additional Information

• Concurrency control is essential in database management systems to ensure the correctness and isolation of transactions.
• Other common concurrency problems include lost updates, dirty reads, and unrepeatable reads.
• Different isolation levels (Read Uncommitted, Read Committed, Repeatable Read, and Serializable) provide different levels of protection against these problems.
• The Serializable isolation level is the most restrictive and ensures complete isolation but can impact performance due to its strict locking mechanisms.