System errors
During system operation different types of errors can
occur. The following table describes some of those errors.
| Category | Description | Example |
|---|---|---|
| User error | An error on the part of the user, usually because of incorrect or invalid input. | Invalid user name, invalid SQL syntax. |
| Component failure | A hardware or software system component failure. | SPU failure; host process crashes. |
| Environment failure | A request of an environment facility fails. This is often because of resource or access problems. | A file is locked; a buffer is full. |
| Recoverable internal error | A detected internal programming error that is not severe enough to abort the program. | Unknown case value or msg type; file close fails. |
| Unrecoverable internal error | A detected internal programming error or a corrupted internal state that requires the program to abort. | Core, memory corruption, assert fails. |
The IBM Netezza Appliance and
IBM Netezza Appliance system can take
the following actions when an error occurs:
- Display an error message
- Presents an error message string to the users that describes the error. This is the common system response whenever a user request is not fulfilled.
- Try again
- During intermittent or temporary failures, keep trying until the error condition disappears. The retries are often needed when resources are limited, congested, or locked.
- Fail over
- Switches to an alternate or spare component because an active component has failed. Failover is a system-level recovery mechanism and can be triggered by a system monitor or an error that is detected by software that is trying to use the component.
- Log the error
- Adds an entry to a component log. A log entry contains a date and time, a severity level, and an error/event description.
- Send an event notification
- Sends notification through email or by running a command. The decision whether to send an event notification is based on a set of user-configurable event rules.
- Abort the program
- Terminates the program because it cannot continue because of an irreparably damaged internal state or because continuing would corrupt user data. Software asserts that detect internal programming mistakes often fall into this category because it is difficult to determine that it is safe to continue.
- Clean up resources
- Frees or releases resources that are no longer needed. Software components are responsible for their own resource cleanup. In many cases, resources are freed locally as part of each specific error handler. In severe cases, a program cleanup handler runs before the program exits and frees/releases any resources that are still held.