This metric represents the number of long table scans per second during sample period. A table is considered 'long' if the table is not cached and if its high-water mark is greater than 5 blocks.
This test checks the long table scans per second. If the value is greater than or equal to the threshold values specified by the threshold arguments, and the number of occurrences exceeds the value specified in the "Number of Occurrences" parameter, then a warning or critical alert is generated.
The rest of the information in this section is only valid for this metric when it appears in either the Enterprise Manager Grid Control or the Enterprise Manager Database Control (if applicable).
The following table shows how often the metric's value is collected and compared against the default thresholds. The 'Consecutive Number of Occurrences Preceding Notification' column indicates the consecutive number of times the comparison against thresholds should hold TRUE before an alert is generated.
|
Target Version |
Evaluation and Collection Frequency |
Upload Frequency |
Operator |
Default Warning Threshold |
Default Critical Threshold |
Consecutive Number of Occurrences Preceding Notification |
Alert Text |
|
pre-10g |
Every 5 Minutes |
After Every Sample |
> |
Not Defined |
Not Defined |
2 |
Rate of scans on long tables is %value%/sec. |
|
Target Version |
Server Evaluation Frequency |
Collection Frequency |
Upload Frequency |
Operator |
Default Warning Threshold |
Default Critical Threshold |
Consecutive Number of Occurrences Preceding Notification |
Alert Text |
|
10.1.0.x; 10.2.0.x; 11.1.0.x; 11.2.0.x |
Every Minute |
Not Defined |
After Every Sample |
> |
Not Defined |
Not Defined |
2 |
Generated By Database Server |
DeltaScans / Seconds where:
DeltaScans: difference in 'select value from v$sysstat where name='table scans (long tables)'' between end and start of sample period
Seconds: number of seconds in sample period
A table scan means that the entire table is being scanned record by record in order to satisfy the query. For small tables that can easily be read into and kept in the buffer cache this may be advantageous. But for larger tables this will force a lot of physical reads and potentially push other needed buffers out of the cache. SQL statements with large physical read and logical read counts are candidates for table scans. They can be identified either through the Top SQL page sorted by Physical Reads, or through the Top Sessions page sorted by Physical Reads, with a drilldown to the current SQL for a session.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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