This metric represents the number of logical reads per second during the sample period. A logical read is a read request for a data block from the SGA. Logical reads may result in a physical read if the requested block does not reside with the buffer cache.
This test checks the logical(db block gets + consistent gets) reads 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 |
Session logical reads are %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 |
LogicalReads / Seconds where:
LogicalReads: difference in 'select value from v$sysstat where name='session logical reads'' between end and start of sample period
Seconds: number of seconds in sample period
Excessive logical reads, even if they do not result in physical reads, can still represent an area that should be considered for performance tuning. Typically large values for this statistic indicate that full table scans are being performed. To identify the SQL that is performing the most logical reads (buffer gets), use the Top SQL page sorted by Buffer Gets. This quickly identifies the SQL responsible for the bulk of the logical reads. You can further investigate these SQL statements via drilldowns. Tuning these SQL statements will reduce your buffer cache access.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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