JDBC Interview Questions

1. ACID Properties in DBMS?
1. A transaction is a single logical unit of work which accesses and possibly modifies the contents of a database. Transactions access data using read and write operations.In order to maintain consistency in a database, before and after transaction, certain properties are followed. These are called ACID properties.
2. Atomicity
1. By this, we mean that either the entire transaction takes place at once or doesn’t happen at all. There is no midway i.e. transactions do not occur partially. Each transaction is considered as one unit and either runs to completion or is not executed at all. 
3. Consistency
1. This means that integrity constraints must be maintained so that the database is consistent before and after the transaction. It refers to correctness of a database. 
4. Isolation
1. This property ensures that multiple transactions can occur concurrently without leading to inconsistency of database state. Transactions occur independently without interference. Changes occurring in a particular transaction will not be visible to any other transaction until that particular change in that transaction is written to memory or has been committed. This property ensures that the execution of transactions concurrently will result in a state that is equivalent to a state achieved these were executed serially in some order.
5. Durability
1. This property ensures that once the transaction has completed execution, the updates and modifications to the database are stored in and written to disk and they persist even is system failure occurs. These updates now become permanent and are stored in a non-volatile memory.
6. The effects of the transaction, thus, are never lost.