DB2 Server for VM: System Administration

Chapter 9. Making Backups and Recovering from Failures

Database recovery refers to the processing done to correct data when something goes wrong. This chapter presents a detailed description of basic recovery concepts, and how to implement them. More advanced recovery topics are discussed in Chapter 10, Special Topics in Recovery Design.

The problems that can occur fall into four categories:

Application Error
Occurs when an application (for example, an ISQL command or routine, or the DBS utility) does not end successfully.

User Logic Error
Occurs when the system or application does the requested function, but the request itself is in error -- that is, the user (or application program) did not specify the correct function. For example, the user may have accidentally dropped the wrong table or dbspace.

This is the only type of error where detection is not immediate. Therefore, it presents more of a problem. Errors in the data can go undetected for quite some time, making recovery processing very complex.

System Failure
Occurs when the application server ends abnormally. Such failures can occur because of a severe error involving the operating system, or because of certain error conditions detected by the database manager, such as a power failure.

DASD Failure and Database Corruption
Occurs when the database manager cannot read data from or write it to the DASD where it is stored, because the storage medium is unreadable or damaged. Such an error (also called a media failure) can occur on the log, the directory, or a data extent (DBEXTENT).

This manual discusses how to recover from system and DASD failures. Recovery from application and user logic errors is described in the DB2 Server for VSE & VM Database Administration manual.

There are two aspects to dealing with system and DASD failures:

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