Lecture 10. Transaction Management, Transaction Serialization

Maintenance of the transaction mechanism is an indicator of the level of development of the DBMS. Proper maintenance of transactions at the same time is the basis for ensuring the integrity of the database (and therefore transactions are quite appropriate in single-user personal DBMS), and also form the basis of user isolation in multi-user systems. Often these two aspects are considered separately, but in fact they are interrelated, as will be shown in this lecture.

Note that although from the point of view of ensuring the integrity of databases, the transaction mechanism should be maintained in personal DBMSs, in practice this is not usually done. Therefore, when moving from personal to multi-user DBMS, users are faced with the need for a clear understanding of the nature of transactions.

A transaction is understood to be indivisible from the point of view of the impact on the database, the sequence of data manipulation statements (read, delete, insert, modify) is such that either the results of all operators included in the transaction are displayed in the database, or the impact of all these operators is completely absent. The transaction slogan is “All or Nothing”: when a transaction is completed with a COMMIT statement, the results are guaranteed to be recorded in external memory (the meaning of the word commit is to “fix” the results of the transaction); when a transaction is completed by the ROLLBACK operator, the results are guaranteed to be absent in the external memory (the meaning of the word rollback is to eliminate the results of the transaction).