Redo log entries contain a record of changes that have been made to the database block buffers. The log writer (LGWR) process writes redo log entries from the log buffer to a redo log file. The log buffer should be sized so that space is available in the log buffer for new entries, even when access to the redo log is heavy. When the log buffer is undersized, user process will be delayed as they wait for the LGWR to free space in the redo log buffer.
The redo log buffer efficiency, as measured by the hit ratio, records the percentage of times users did not have to wait for the log writer to free space in the redo log buffer.
This metric monitors the redo log buffer hit ratio (percentage of success) against the values specified by the threshold arguments. If the number of occurrences is smaller than the values specified, 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 |
Redo log allocation hit ratio is %value%%%. |
|
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 |
100 * (redo_entries_delta - redo_space_requests_delta) /redo_entries_delta where:
redo_enties_delta = difference between "SELECT value FROM v$sysstat WHERE name = 'redo entries'" at the beginning and ending of the interval
redo_space_requests_delta = difference between "SELECT value FROM v$sysstat WHERE name = 'redo log space requests'" at the beginning and ending of the interval
The LOG_BUFFER initialization parameter determines the amount of memory that is used when buffering redo entries to the redo log file.
Consider increasing the LOG_BUFFER initialization parameter in order to increase the size of the redo log buffer. Redo log entries contain a record of the changes that have been made to the database block buffers. The log writer process (LGWR) writes redo log entries from the log buffer to a redo log. The redo log buffer should be sized so space is available in the log buffer for new entries, even when access to the redo log is heavy.
Note: For Oracle Management Agent release 9i, this metric has been obsoleted. It is recommended that you use the Redo NoWait Ratio metric. This metric is kept for backward compatibility with older versions of the Management Agent.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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