Oracle RAC PGA Test

A PGA is a memory region that contains data and control information for a server process. It is nonshared memory created by Oracle Database when a server process is started. Access to the PGA is exclusive to the server process. There is one PGA for each server process. Background processes also allocate their own PGAs.

If the PGA runs out of memory, then critical server processes may not run. To avoid this, administrators can use the Oracle RAC PGA test to keep an eye on the memory consumed by the PGA and be proactively alerted to one/more server processes that are draining memory from the PGA rapidly.

Note:

This test will not report metrics for an Oracle 12c PDB server.

Target of the test : Oracle RAC

Agent deploying the test : An internal agent

Outputs of the test : One set of results for each node in the Oracle cluster being monitored

Configurable parameters for the test
  1. TEST PERIOD - How often should the test be executed.
  2. Host – The host for which the test is to be configured.
  3. Port - The port on which the server is listening.
  4. orasid - The variable name of the oracle instance.
  5. 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 ServiceName of a cluster, execute the following query on any node in the target cluster:

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

  6. User – 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.

  7. Password – Password of the specified database user
  8. Confirm password – Confirm the password by retyping it here.
Measurements made by the test
Measurement Description Measurement Unit Interpretation

Current size

Indicates the amount of PGA memory that is currently in use.

MB

Ideally, the value of this measure should be low. A steady rise in this value is a sign of excessive consumption of PGA memory by server processes.

PGA hit ratio

Indicates the ratio of  the total number of bytes processed in the PGA versus the total number of bytes processed plus extra bytes read/written in extra passes.

Percent

A value of 100% means that all work areas executed by the system since instance startup have used an optimal amount of PGA memory.

If the value of this measure falls below 95%, it indicates that the work area cannot run optimal. As a result, one or more extra passes will be performed over the input data. In this case therefore, you can take one of the following actions:

  • When not using Automatic PGA memory, then increase SORT_AREA_SIZE init parameter.
  • When using Automatic PGA memory, then increase PGA_AGGREGATE_TARGET init parameter.

PGA usage ratio

Indicates the percentage of PGA memory that is consumed by the server processes.

Percent

Ideally, the value of this measure should be low. If this value rapidly approaches 100%, it indicates that the PGA is about to run out of free memory. You may then want to consider resizing your PGA memory region by increasing the value for the PGA_AGGREGATE_TARGET init parameter.