Oracle RAC Archive Area Test

An Oracle Cluster database can run in one of two modes. By default, the database is created in NOARCHIVELOG mode. When in NOARCHIVELOG mode the cluster database runs normally, but there is no capacity to perform any type of point in time recovery operations or online backups. In ARCHIVELOG mode on the other hand, the cluster database will make copies of all online redo logs after they are filled. These copies are called archived redo logs. The archived redo logs are created via the ARCH process. The ARCH process copies the archived redo log files to one or more archive log destination directories.

Note that while the cluster database is being run in the ARCHIVELOG mode, then once an online redo log has been filled, it cannot be reused until it has been archived. If, in the meantime, the destination directory for the archived redo logs runs out of space, then Oracle cluster cannot archive the online redo log. Instead, it will switch to the next online redo log and keep working, while continuing its efforts to archive the log file.

If the cluster database is unable to archive the redo log files for a long time, then at some point it might run out of available online redo logs. Since it cannot reuse the unarchived redo logs for writing the new redo log entries, the cluster database freezes all its operations and stops processing user requests until such time that space is freed in the archive log destination directories.

To ensure that the Oracle Cluster database is always available to process requests, administrators need to ensure that the archive log destination directories are adequately sized.

The Oracle RAC Archive Area test periodically monitors the usage of the archive log destination directories, and warns administrators about a sudden/consistent decrease in the free space available in the directories. This enables administrators to act fast and free sufficient space in the directories, so as to prevent the Oracle Cluster database from suspending its activities.

Note:

For this test to work;

  • The eG install user should be in the Oracle User Group.
  • The cluster database should run in ARCHIVELOG mode

Target of the test : An Oracle Cluster

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each archivelogfile configured/auto-discovered on the target Oracle Cluster 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.

Service Name

A ServiceName exists for the entire Oracle RAC system. When clients connect to an Oracle cluster using the ServiceName, then the cluster routes the request to any available database instance in the cluster. By default, the Service Name is set to none. In this case, the test connects to the cluster using the ORASID and pulls out the metrics from that database instance which corresponds to that ORASID. If a valid service name is specified instead, then, the test will connect to the cluster using that Service Name, and will be able to pull out metrics from any available database instance in the cluster.

To know the Service Name of a cluster, execute the following query on any node in the target cluster:

select name, value from v$parameter where name =’service_names’

ORASID

The variable name of the oracle instance.

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.

ArchiveFilePath

By default, the eG agent auto-discovers the location of the Oracle archive log file. This is why, the ArchiveFilePath parameter is set to none by default. If required, you can manually specify the path to the Oracle archive log file to be monitored. For eg, /user/john/archive

Measurements made by the test
Measurement Description Measurement Unit Interpretation

Used archive area

Indicates the space currently occupied by the archive files in the archive destination directory.

MB

 

Used drive space

Indicates the space in the archive destination drive that is currently occupied by all files, including archive files.

MB

 

 

Relative archive area usage

Indicates the percentage of total used space in the archive destination drive, which is occupied by the archive files.

Percent

This measurement value should ideally be below 50%. Any value higher than 50%, indicates that the archive files are consuming more space than the other files in the archive destination drive. To free some space in that drive,  you can adopt any of the following approaches:

  • Add more disk space to the archive drive;
  • Take backups of the old archive files to tape or to another destination, and remove them from the destination directory;
  • Temporarily, you can even zip all archive files in the archive destination.

Available drive space

Indicates the current free space in the archive destination.

MB

 

Percent drive space free

Indicates the percentage of unused space in the archive destination.

Percent

This measurement value should ideally be high. If the value is consistently low, you may want to check the value of the Relative archive area usage measure to determine what is causing the space drain - is it because of the archive files, or the other files in the archive destination drive? If the archive files appear to be consuming excessive space in the drive, you can free some space in the drive by adopting any of the following approaches:

  • Add more disk space to the archive drive;
  • Take backups of the old archive files to tape or to another destination, and remove them from the destination directory;
  • Temporarily, you can even zip all archive files in the archive destination.

Archive area growth rates

Indicates the rate at which archive files occupied space in the archive destination directory.

MB/Sec

Ideally, the value of this measure should be low. A consistent increase in this value is a cause for concern as it indicates that free space in the archive destination directory is getting eroded at a rapid pace. This in turn hints at a potential space crunch in the directory, which if not averted, could cause the performance of the Oracle Cluster database server to deteriorate.