Method and apparatus for providing isolation levels in a databas

Details Method and apparatus for providing isolation levels in a databas Method and apparatus for providing isolation levels in a databas

1996-03-11

1999-02-09

Black, Thomas G.

Data processing: database and file management or data structures

Database design

Data structure types

707 8, 707202, 707203, G06F 1740

Patent

active

058707581

ABSTRACT:
A method and system for providing isolation levels in a database system is provided. A serializable isolation level is provided by causing all statements in a transaction to see a "snapshot" of the database. A snapshot includes only those changes made to the database by a particular set of transactions. For example, the snapshot for a given transaction may include only the changes made by transactions that committed prior to the execution of the given transaction. The set of all transactions whose changes are included in a particular snapshot of the database is referred to as the snapshot set. Concurrently executing transactions may update the database while a serializable transaction is being executed. Updates that are not included in the snapshot of the serializable transaction are undone prior to processing each statement in the serializable transaction to recreate the data as it existed in the snapshot. If a serializable transaction attempts to update data that was updated by a transaction that is not in the snapshot set of the serializable transaction, then the serializable transaction is rolled back. A read committed isolation level is provided by establishing a different snapshot for each statement in a transaction.

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