[Database] Race condition

A race condition is a type of bug that occurs when multiple transactions (threads or processes) access a shared resource simultaneously, and might cause abnormal behavior.

Dirty read

• A transaction reads data that another transaction hasn’t been committed.
• Occur when an UPDATE, INSERT, DELETE from another transaction.

Read skew (Non-repeatable read)

• A transaction reads inconsistent data because another transaction modify and commit the data during the course of a transaction.
• Occur when an UPDATE from another transaction.

Phantom read

• A transaction reads inconsistent data because another transaction modify and commit the data during the course of a transaction.
• Occur when an INSERT, DELETE from another transaction.

Lost update

• Multiple transactions are trying to modify the same data at the same time, and one of a transaction overwrite modifications from other transactions.
• Occur when an UPDATE from another transaction.

Write skew

• Multiple transactions read the same data first for modifying, but one of a transaction modify the data and commit before other transactions.
• Occur when an UPDATE, INSERT, DELETE from another transaction.