Isolatsioonitaset

Isolatsioonitaset, also known as isolation level, is a concept in database management systems that defines the degree to which transactions are isolated from each other. It ensures that the operations within a transaction are not affected by other concurrent transactions, maintaining data integrity and consistency. There are four standard isolation levels, each with its own trade-offs between performance and data accuracy.

The first isolation level is Read Uncommitted, which allows a transaction to read uncommitted changes made by other transactions. This level provides the highest level of concurrency but the lowest level of data integrity, as it can lead to dirty reads, where a transaction reads data that has been modified by another transaction but not yet committed.

The second isolation level is Read Committed, which ensures that a transaction can only read data that has been committed by other transactions. This level prevents dirty reads but can still result in non-repeatable reads, where a transaction reads the same data twice and gets different results due to changes made by other transactions.

The third isolation level is Repeatable Read, which guarantees that if a transaction reads a data item, any subsequent read operations within that transaction will yield the same result. This level prevents non-repeatable reads but can still lead to phantom reads, where a transaction reads a set of rows that satisfy a condition, and another transaction inserts a new row that satisfies the same condition, causing the first transaction to see additional rows in subsequent reads.

The fourth and highest isolation level is Serializable, which ensures that transactions are completely isolated from one another, as if they were executed sequentially. This level prevents dirty reads, non-repeatable reads, and phantom reads but can significantly reduce concurrency and performance.

Choosing the appropriate isolation level depends on the specific requirements of the application, balancing the need for data consistency with the need for performance and concurrency.