Database Isolation Levels

Database isolation levels determine the degree to which concurrent transactions can see the effects of each other. They are used to manage concurrency and ensure data integrity in a multi-user environment.

Here are the four primary isolation levels:

1. Read Uncommitted:

• This is the lowest isolation level.
• Transactions can read data that has not yet been committed by other transactions.
• This can lead to dirty reads, where a transaction reads data that is later rolled back.

2. Read Committed:

• Transactions can only read data that has already been committed by other transactions.
• This prevents dirty reads, but can still lead to non-repeatable reads and phantom reads.
• A non-repeatable read occurs when a transaction reads the same data multiple times and gets different results.
• A phantom read occurs when a transaction reads a set of rows and then inserts or deletes rows that meet the same criteria, causing the transaction to read a different set of rows when it repeats the query.

3. Repeatable Read:

• Transactions can read data multiple times and get consistent results.
• This prevents dirty reads and non-repeatable reads, but can still lead to phantom reads.

4. Serializable:

• This is the highest isolation level.
• Transactions are executed sequentially, as if they were the only transactions in the system.
• This prevents dirty reads, non-repeatable reads, and phantom reads, but can significantly reduce concurrency.

Choosing the appropriate isolation level is a trade-off between concurrency and data integrity. Higher isolation levels provide stronger data integrity but lower concurrency, while lower isolation levels provide higher concurrency but weaker data integrity.

It’s important to note that different database systems may implement isolation levels differently, so it’s essential to consult the documentation for the specific database system we are using.