LUW

LUW, short for Logical Unit of Work, is a concept used in database management to describe a sequence of operations that the database management system treats as a single, indivisible transaction. A LUW begins when a transaction is started and ends when it is either committed or rolled back. All the statements and changes performed within a LUW are part of the same logical unit.

Key characteristics of a LUW include atomicity, consistency, isolation, and durability (ACID). Atomicity ensures that either all changes within the LUW are applied or none are; rollback can undo partial work. Consistency requires that a LUW moves the database from one valid state to another valid state. Isolation ensures that concurrent LUWs do not interfere with each other, according to the configured isolation level. Durability guarantees that once a LUW is committed, its changes survive system failures.

In practice, LUWs are implemented through the database’s logging and recovery mechanisms. Changes are recorded in logs, enabling undo and redo during recovery after a crash. For distributed systems, a LUW may span multiple resource managers and use a two-phase commit protocol to achieve global atomicity.

A typical LUW includes multiple SQL statements, such as a fund transfer that debits one account and credits another within the same LUW. If any part fails, the entire LUW is rolled back. LUWs are distinct from individual statements and are defined by their commit or rollback boundaries rather than by a single SQL command.