When several transactions read and write items in a database, the question of consistency of the database arises. Consistency is maintained if transactions are serial: the read and write actions of a transaction execute completely before the actions of the next transaction begin. A particular history of interleaved read and write actions belonging to several transactions is correct if it is equivalent to a serial history. Since serializability of histories is known to be NP-complete, subclasses of serializable histories have been studied. One such class consists of histories serializable in a strict sense; transactions that are already in serial in a history must remain in the same relative order. When there are no useless actions in a history, it is shown that strict serializability can be determined in polynomial time. If useless actions are permitted, then strict serializability becomes NP-complete. The results apply to two-step transactions in which there is a read step followed by a write step. Each step involves some subset of the items in the database. With multistep transactions strict serializability is NP-complete even if there are no useless actions.
ASJC Scopus subject areas
- Computational Theory and Mathematics
- Computer Graphics and Computer-Aided Design
- Hardware and Architecture
- Information Systems
- Theoretical Computer Science