This metric represents the number of redo write operations per second during this sample period.
The redo log buffer is a circular buffer in the SGA that holds information about changes made to the database. This information is stored in redo entries. Redo entries contain the information necessary to reconstruct, or redo, changes made to the database by INSERT, UPDATE, DELETE, CREATE, ALTER or DROP operations. Redo entries are used for database recovery, if necessary.
The log writer process (LGWR) is responsible for redo log buffer management; that is, writing the redo log buffer to a redo log file on disk.
This test checks the number of writes by LGWR to the redo log files per transaction. 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 |
Redo write rate is %value%/transaction. |
|
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 |
DeltaRedoWrites /(DeltaCommits+DeltaRollbacks) where:
DeltaRedoWrites: difference in 'select s.value from v$sysstat s, v$statname n where n.name='redo writes' and n.statistic#=s.statistic#' between sample end and start
DeltaCommits: difference in 'select s.value from v$sysstat s, v$statname n where n.name='user commits' and n.statistic#=s.statistic#' between sample end and sample start
DeltaRollbacks: difference in 'select s.value from v$sysstat s, v$statname n where n.name='user commits' and n.statistic#=s.statistic#' between sample end and sample start
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 to increase the size of the redo log buffer should waiting be a problem. 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.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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