| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Current_usage |
Indicates the current actual usage with respect to the current allocated size (Current_size) |
Percent |
As a rule of thumb, at any time, about 20% of the space allocated to a tablespace should be available. In case of auto-extensible tablespaces, even if this percentage touches 100%, there would be no cause for concern. However, if a tablespace is not auto-extensible, then when the percentage disk space usage reaches 100%, all statements that attempt to acquire new space in the tablespace will fail. Under such circumstances, the underlying datafiles of the tablespace may need to be resized or reorganized. Alternately, additional datafiles could be mapped to the tablespace. |
| Physical_read_rate |
Indicates the rate of physical reads happening on a tablespace. |
Reads/Sec |
A sudden increase in the rate of data accesses may indicate a change in application characteristics. At any stage, if more than 50% of the total reads for a database instance happen to be on a particular tablespace, this may
result in performance degradation. |
| Physical_write_rate |
Indicates the rate of physical writes happening on a tablespace. |
Writes/Sec |
More than 50% of the total writes for a database instance happening on a particular tablespace may be indicative of a problem scenario that needs further investigation. |
| Auto_extensible |
Indicates whether the tablespace has the capability to grow automatically or not |
|
If the tablespace is auto-extensible, then this measure will report the value Yes. If it is not extensible, then the value of this measure will be No.
The numeric values that correspond to the measure values discussed above are as follows:
| Measure Value |
Numeric Value |
| Yes |
1 |
| No |
0 |
Note:
By default, the measure reports the Measure Values listed in the table above to indicate whether/not a tablespace is auto-extensible. In the graph of this measure however, the same is represented using the numeric equivalents only. |
| Max_size |
Indicates the maximum extent (in MB) upto which a tablespace can grow |
MB |
|
| Current_size |
Indicates the "current allocated size" for the tablespace |
MB |
If a tablespace is not auto-extensible, then its Current_size will be equal to the Max_size. For auto-extensible tablespaces though, the values of the Current_size and Max_size measures could be different. |
| Free_space |
Indicates the amount of unused space in the tablespace. This is computed using the formula: Max_size - Current actual usage, where Current actual usage is arrived at by applying the Current_usage percentage on the Current_size (current allocated size) measure. For example, assume that the Max_size of a tablespace is 2500 MB and its Current_size is 1000 MB. Also, note that nearly 30% of the Current_size has already been utilized. Therefore, the Current actual usage of the tablespace will be 30% of 1000MB, which is 300 MB. The available Free_space will hence be, 2500-300, i.e. 2200 MB. |
MB |
If this value is very low, then it indicates over-utilization of the tablespace. |
| Pct_free_space |
Indicates the space available for "overall growth" expressed as a percentage of Free_space with respect to the Max size of the tablespace. The formula used is: Free_space/Max_size*100 |
Percent |
If this value is very low, then it indicates over-utilization of the tablespace. |
| Biggest_extent |
Indicates the size of the biggest extent in the tablespace |
MB |
From both these values, you can figure out how space allocation, fragementation, etc. have been performed on the tablespace. |
| Smallest_extent |
Indicates the size of the smallest extent in the tablespace |
MB |
| Remaining_extents |
Indicates the number of extents that can be added to a tablespace. |
Number |
If this value is low and the tablespace is not auto-extensible, then it indicates that
the tablespace requires resizing. In the case of auto-extensible tablespaces, this phenomenon is not a cause for concern. Note that this measure is applicable only to the tablespaces that have dictionary-based extent management and allocation type is user. |