eG Monitoring
 

Measures reported by OraRacDgLogGapTest

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 OraRacDgLogGapTest 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.

Outputs of the test : One set of results for each database instance: destination to which the redo log files are to be archived from the target Oracle Cluster database server being monitored.

The measures made by this test are as follows:

Measurement Description Measurement Unit Interpretation
Log_seq_archived Indicates the number of log sequences received at this archived redo log destination. Number  
Log_seq_applied Indicates the number of log sequences applied to this archived redo log destination. Number  
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.
Log_gap_status Indicates the current status of the redo logs in this archived redo log destination.   The values reported by this measure and its numeric equivalents are mentioned in the table below:

Measure Value Numeric Value
No gap 0
Resolvable gap 1
Log switch gap 2
Unresolvable gap 3
Locally unresolvable gap 4


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.