Repeatable Read is a database isolation level that ensures if a transaction reads a value from the database, it will read the same value throughout the transaction, preventing non-repeatable reads. However, it does not protect against phantom reads, where new rows can be added by other transactions and become visible within the same transaction.

Repeatable Read

database isolation level

transaction reads

same value

Non-repeatable reads occur when a transaction reads the same row twice and gets different data each time due to another transaction modifying the data between reads. This phenomenon is a result of concurrency issues in database systems and is typically addressed using isolation levels like 'Repeatable Read' or higher to ensure data consistency.

non-repeatable reads

Phantom reads occur in database systems when a transaction reads a set of rows that satisfy a certain condition, and a subsequent read within the same transaction returns additional rows due to another transaction inserting new rows that meet the condition. This phenomenon is a result of concurrency and can be mitigated by using higher isolation levels like Serializable to ensure consistency.

Relevant Degrees

Log in to see lessons