1 / 5

Isolation Levels

Isolation Levels. Phantoms a phantom with respect to transaction T1 is a new record that comes into existence, created by a concurrent transaction T2, that satisfies a search condition used by T1 consider transactions that include the following operations:. T1 SELECT * FROM a

ehirsch
Download Presentation

Isolation Levels

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Isolation Levels • Phantoms • a phantom with respect to transaction T1 is a new record that comes into existence, created by a concurrent transaction T2, that satisfies a search condition used by T1 • consider transactions that include the following operations: T1 SELECT * FROM a WHERE id BETWEEN 5 AND 10 T2 INSERT INTO a VALUES (id,name) (7,’joe’)

  2. Interactive transactions • values written to a user terminal prior to commit could be used as input to other transactions • this inter-transaction dependency is outside the scope of any DBMS concurrency controls

  3. SQL isolation levels • SET TRANSACTION • < SERIALIZABLE | • REPEATABLE READ | • READ COMMITTED | • READ UNCOMMITTED > • Reference: Data and databases: concepts in practice; Joe Celko; 1999; Morgan Kaufmann Publishers; ISBN 1-55860-432-4

  4. Phenomena description • P1 dirty read • (transaction can read data that is not committed) • P2 nonrepeatable read • (transaction can read the same row twice, • and it could be different) • P3 phantom

  5. Phenomena occurs? P1 P2 P3 serializable no no no repeatable read no no yes read committed no yes yes read uncommitted yes yes yes

More Related