Thresholds - IBM DB2 9.7 for Linux, UNIX, and Windows

For storage management, thresholds are used to monitor the storage usage of your database.

In the Storage Management view, you can set warning and alarm thresholds for the Storage Management tool to compare against the real time readings of the system. If an object's storage state exceeds the safe levels, or thresholds, that you have set for it, an alert flag will be shown beside the object in the Storage Management view.

When a database is created, there are default thresholds set for the database object. All of its children (objects within the database scope) inherent the default threshold. However, you can overwrite the default thresholds by providing specific values for any of the objects. Once a threshold is set for an object, all the objects defined under its scope will inherit its threshold setting, unless otherwise specified.

The Storage Management view monitors three types of thresholds: space usage, data skew, and cluster ratio.

Space usage measures the percentage of available storage space that is used by an object. Space usage is monitored through table spaces. The space usage of an object is represented as a percentage of total storage space, with a value of 0 to 100.
Data skew measures the distribution of data by measuring an object's deviation from the average data level, as a percentage. The data skew is monitored through tables and database partition groups. When a data skew threshold is exceeded, the Redistribute Data wizard can be used to even out data distribution differences among the database partitions in the database partition group. The disk skew of an object is represented as a percentage showing the object's deviation from the average data level, ranging from -100 to 100. A negative integer indicates that the data level is less that the average data level; an positive data level indicates that the data level is greater than the average.
Cluster ratio measures the degree to which the rows in a table are arranged in the same order specified by a given index. A higher cluster ratio indicates that the data rows are stored in the same physical sequence as the index. A low cluster ratio indicates the index and data rows are stored in a different physical sequence. Cluster ratio is represented as a percentage, with a value of 0 to 100.

In the Health Center, the criteria for the health indicators that measure a continuous range of values is defined in terms of thresholds. Thresholds define boundaries or zones and are configured as single-bounded with either increasing or decreasing values. There are three boundaries or zones: normal, warning, and alarm. If the value of a health indicator falls into the warning zone, a warning alert is issued. Similarly, if the indicator value falls into the alarm zone, an alarm alert is generated.