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| Topics for Database Administrators |
Enabling the Rollback Log
A single SAS observation can be composed of one or more SYSTEM 2000 database records. Therefore, a single UPDATE command in SYSTEM 2000 to update a given observation might involve several internal SYSTEM 2000 UPDATE commands. If one of these UPDATE commands fails after several others have executed, the status of the entire update is incomplete.
In order to guarantee the data integrity, you must enable the rollback feature. You can do this easily with the QUEST procedure, by issuing the ENABLE ROLLBACK statement in the CONTROL language. When you enable rollback, you must make sure that the Rollback Log (database File 8) and the Update Log (database File 7) are allocated. With rollback enabled, SYSTEM 2000 can roll back the database to its status before the sequence of commands that triggered the error.
If rollback is not enabled, partial updates can occur if error return codes are received. Errors can occur from security violations or from bad data, for example, data that does not match the SAS informat, or data that has too many significant decimal places for a specific item's numerical precision. Also, if LHOLD=YES is specified in the SYSTEM 2000 execution parameters and rollback is not enabled, the interface view engine can receive return code 111, which causes an update to be rejected.
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