202 | Chapter 9: Oracle and Transaction Processing
What Is a Transaction?
The concept of a transaction and the relevant Oracle mechanics for dealing with
transactions were discussed in Chapter 8. To recap that discussion, a transaction is a
logical unit of work that must succeed or fail in its entirety. Each transaction typically
involves one or more Data Manipulation Language (DML) statements such as
INSERT, UPDATE, or DELETE, and ends with either a COMMIT to make the
changes permanent or a ROLLBACK to undo the changes.
The industry bible for OLTP, Transaction Processing: Concepts and Techniques, by
Jim Gray and Andreas Reuter (Morgan Kaufmann; see Appendix B), introduced the
notion of the ACID properties of a transaction. A transaction must be the following:
Atomic
The entire transaction succeeds or fails as a complete unit.
Consistent
A completed transaction leaves the affected data in a consistent or correct state.
Isolated
Each transaction executes in isolation and doesn??™t affect the states of others.
Durable
The changes resulting from committed transactions are persistent.
Pages:
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450