INTERVIEW QUESTIONS J2EE EJB DETAILS

Question: What are the various isolation levels in a transaction and differences between them?

Answer: There are three isolation levels in Transaction. They are 1. Dirty reads 2.Non repeatable reads 3. Phantom reads.

Dirrty Reads If transaction A updates a record in database followed by the transaction B reading the record then the transaction A performs a rollback on its update operation, the result that transaction B had read is invalid as it has been rolled back by transaction A.

NonRepeatable ReadsIf transaction A reads a record, followed by transaction B updating the same record, then transaction A reads the same record a second time, transaction A has read two different values for the same record.

Phantom ReadsIf transaction A performs a query on the database with a particular search criteria (WHERE clause), followed by transaction B creating new records that satisfy the search criteria, followed by transaction A repeating its query, transaction A sees new, phantom records in the results of the second query.

There are three isolation levels in Transaction. They are 1. Dirty reads 2.Non repeatable reads 3. Phantom reads.

Dirrty Reads If transaction A updates a record in database followed by the transaction B reading the record then the transaction A performs a rollback on its update operation, the result that transaction B had read is invalid as it has been rolled back by transaction A.

NonRepeatable ReadsIf transaction A reads a record, followed by transaction B updating the same record, then transaction A reads the same record a second time, transaction A has read two different values for the same record.

Phantom ReadsIf transaction A performs a query on the database with a particular search criteria (WHERE clause), followed by transaction B creating new records that satisfy the search criteria, followed by transaction A repeating its query, transaction A sees new, phantom records in the results of the second query. Source: CoolInterview.com

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