Relational Theory for Computer Professionals: What Relational Databases Are Really All About by C.J. Date

Author:C.J. Date
Language: eng
Format: epub
Tags: COMPUTERS / Programming Languages / SQL
ISBN: 9781449369446
Publisher: O’Reilly Media
Published: 2013-05-20T16:00:00+00:00

Unsuccessful termination: ROLLBACK “rolls the database back” to the state it was in when the transaction began (thereby undoing the transaction’s updates) and terminates the transaction.

Implicit ROLLBACK: The code in the dollar transfer example includes explicit tests for errors and forces an explicit ROLLBACK if it detects one. But we obviously can’t assume, nor would we want to assume, that transactions always include explicit tests for all possible errors that might occur. Therefore, the system will force an implicit ROLLBACK for any transaction that fails to reach its planned termination for any reason, where “planned termination” means either an explicit COMMIT or an explicit ROLLBACK. Moreover, if there’s a system crash (in which case the transaction will fail through no fault of its own), then, when the system restarts, it will typically try to run the transaction again.

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