Atomic commit: Difference between revisions

Revision as of 01:31, 28 May 2015

Revision as of 16:07, 27 July 2015

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Atomic commits are essential for multi-step updates to data. This can be clearly shown in a simple example of a money transfer between two checking accounts.<ref>{{Cite book |first1=Hector |last1=Garcia-Molina |first2=Jeff |last2=Ullman |first3=Jennifer |last3=Widom |title=Database Systems The Complete Book |page=299 |publisher=Prentice Hall |year=2009}}</ref>

This example is complicated by a transaction to check the balance of account Y during a transaction for transferring 100 dollars from account X to Y. To start, first 100 dollars is removed from account X. Second, 100 dollars is added to account Y. If the entire operation is not completed as one atomic commit, then several problems could occur. If the system fails in the middle of the operation, after removing the money from X and before adding into Y, then 100 dollars has just disappeared. Another issue is if the balance of Y is checked before the 100 dollars is added., Thethe wrong balance for Y will be reported.

With atomic commits neither of these cases can happen, in the first case of the system failure, the atomic commit would be rolled back and the money returned to X. In the second case, the request of the balance of Y cannot occur until the atomic commit is fully completed.