Какова роль уровня изоляции repeatable read в обеспечении целостности транзакций в базе данных?

The transaction isolation level repeatable read guarantees that within a single transaction, all repeated reads of the same data will return the same results. This prevents the problem of non-repeatable reads, where data can change between two reads within the same transaction.

Specifically, at the repeatable read level:

• The transaction sees data as it was at the time of the first read.
• Other transactions cannot modify or delete rows that have been read by the current transaction until it completes.

This helps ensure data integrity, preventing situations where one transaction sees different versions of the same data, which is important for correct business logic execution.

However, the repeatable read level does not protect against phantom reads, where new rows can appear as a result of a re-query. To protect against phantom reads, the serializable isolation level is used.