Oracle Dataguard RPO 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 RPO 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.

Configurable parameters for the test
Parameter Description

Test period

How often should the test be executed

Host

The host for which the test is to be configured.

Port

The port on which the server is listening.

Username

In order to monitor an Oracle database server, a special database user account has to be created in every Oracle database instance that requires monitoring. A Click here hyperlink is available in the test configuration page, using which a new oracle database user can be created. Alternatively, you can manually create the special database user. When doing so, ensure that this user is vested with the select_catalog_role and create session privileges.

The sample script we recommend for user creation (in Oracle database server versions before 12c) for eG monitoring is:

create user oraeg identified by oraeg

create role oratest;

grant create session to oratest;

grant select_catalog_role to oratest;

grant oratest to oraeg;

The sample script we recommend for user creation (in Oracle database server 12c) for eG monitoring is:

alter session set container=<Oracle_service_name>;

create user <user_name>identified by <user_password> container=current default tablespace <name_of_default_tablespace> temporary tablespace <name_of_temporary_tablespace>;

Grant create session to <user_name>;                                

Grant select_catalog_role to <user_name>;

The name of this user has to be specified here.

Password

Specify the password of the specified database user.

Confirm Password

Confirm the Password by retyping it here.

IsPassive

If the value chosen is Yes, then the Oracle server under consideration is a passive server in an Oracle cluster. No alerts will be generated if the server is not running. Measures will be reported as “Not applicable" by the agent if the server is not up.

Detailed Diagnosis

To make diagnosis more efficient and accurate, the eG Enterprise embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option.

The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled:

  • The eG manager license should allow the detailed diagnosis capability
  • Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Log sequence archived

Indicates the number of log sequences received at this archived redo log destination.

Number

 

Log sequence 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.