Oracle RAC Session Waits Test

This test reports the number and nature of session wait events that occurred on each instance of the monitored RAC during the last measurement period. In addition, the test also reports the total number of events (of a type) that occurred across all instances. With the help of these metrics, administrators can figure out how much time an instance has spent waiting and what it was waiting for; a  high value is a cause for concern, as it indicates that the instance has waited too long, and could have consequently suffered significant slowdowns.

This test is disabled by default. To enable the test, go to the enable / disable tests page using the menu sequence : Agents -> Tests -> Enable/Disable, pick the Oracle Cluster as the desired Component type, set Performance as the Test type, choose the test from the disabled tests list, and click on the >> button to move the test to the ENABLED TESTS list. Finally, click the Update button.

Target of the test : Oracle RAC

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for each instance of the monitored Oracle RAC.

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.
  9. 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

Cpu waits:

Indicates the number of times since the last measurement period the sessions on this instance waited for CPU.

Number

Ideally, the value of this measure should be low.

IO waits:

Indicates the total number of times the sessions on this instance waited for user I/O, since the last measurement period.

Number

Some of the user I/O wait events include: BFILE read, buffer read retry, db file parallel read, db file scattered read, db file sequential read, and db file single write.

Ideally, the value of this measure should be low.

Cluster waits:

Indicates the total number of times the sessions on this instance waited for  cluster resources since the last measurement period.

Number

A low value is desired for this measure.

Committed waits:

Indicates the total number of commit waits that have occurred in the sessions of this instance since the last measurement period.

Number

A low value is desired for this measure.

If this measure shows a high value, refer to the detailed diagnosis capability of this measure to identify the sessions that are affected by committed waits.

Transaction lock waits:

Indicates the number of times the sessions on  this instance waited for transaction locks, during the last measurement period.

Number

A low value is desired for this measure. If this measure shows a high value, use the detailed diagnosis of the RAC Transaction Locks test to obtain the detailed report on all the sessions that are affected by the lock waits.

Latch waits:

Indicates the total number of latch waits that have occurred in the sessions of this instance since the last measurement period.

Number

A low value is desired for this measure.

Configuration waits:

Indicates the total number of configuration wait events that occurred in the sessions of this instance during the last measurement period.

Number

Configuration waits are waits caused by inadequate configuration of database or instance resources (for example, undersized log file sizes, shared pool size).

Ideally, the value of this measure should be low.

System IO waits:

Indicates the total number of system I/O wait events that occurred in the sessions of this instance during the last measurement period.

Number

System I/O waits are waits for background process I/O (for example, DBWR wait for ‘db file parallel write’).

Ideally, the value of this measure should be low.

Network waits:

Indicates the total number of times since the last measurement period waits related to network messaging (for example, ‘SQL*Net more data to dblink’, occurred in the sessions of this instance.

Number

A low value is desired for this measure.

Other waits:

Indicates the total number of times since the last measurement period waits that should typically not occur on a system (eg., ‘wait for EMON to spawn’) occurred in the sessions of this instance.

Number

Ideally, the value of this measure should be low.

Subtotal waits:

Indicates the overall number of waits that have occurred since the last measurement period in the sessions of this Oracle instance.

Number

Ideally, the value of this measure should be low.