Oracle Dataguard Log Gap Test
A Data Guard Archive Gap Sequence is a set of archived redo logs that could not be transmitted to the standby site. As a result of an archive gap, the standby database will lag behind the primary database. Usually, a Data Guard archive gap sequence is created as a result of a network outage and when the connection between the primary and the standby site is lost. The archive gap sequence can also occur during the creation of a standby database. If the redo logs that are to be archived are missed out or if a certain sequence of logs are alone missed out, then, it indicates that the primary database and the standby databases are not up-to-date. This may cause critical data loss when database failures occur. To avoid such critical failures, it is essential to monitor the redo logs, redo log gap and the status of the redo log. The Oracle Dataguard Log Gap test helps administrators in this regard!
For each destination to which the redo log files are to be archived, this test reports the count of redo log sequences received and the log sequences applied. The number of log sequences that could not be transmitted to the destination are also reported along with the status of the redo logs.
Target of the test : An Oracle server on which Data Guard feature is enabled
Agent deploying the test : An internal/external agent
Outputs of the test : One set of results for each destination to which the redo log files are to be archived from the target Oracle Database server being monitored.
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Measurement | Description | Measurement Unit | Interpretation | ||||||||||||
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Log sequence archived |
Indicates the number of log sequences received at this archived redo log destination. |
Number |
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Log sequence applied |
Indicates the number of log sequences applied to this archived redo log destination. |
Number |
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Log gap |
Indicates the number of log sequences that could not be transmitted to this archived redo log destination. |
Number |
An archive gap can occur whenever the primary database archives a log locally, but the log is not received at the standby site. Every minute, the primary database polls its standby databases to see if there are gaps in the sequence of archived redo log files. If too many gaps are detected in the sequence of the archived redo log files, then, it implies that the primary and the standby databases are not up-to-date. A consistent increase in the value of this measure reduces the efficiency of the database consistently. |
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Log gap status |
Indicates the current status of the redo logs in this archived redo log destination. |
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The values reported by this measure and its numeric equivalents are mentioned in the table below:
Note: By default, this measure reports the current status of the redo logs in this archived redo log destination. The graph of this measure however, is represented using the numeric equivalents only - 0 to 4. |