Oracle RAC DB Wait Time Test

Oracle’s response time for an operation is composed of time executing (=CPU time) and time spent waiting (=Waiting time). An increase in either or both the above-mentioned factors will adversely impact the responsiveness of the Oracle cluster service.

When Oracle executes an SQL statement, it is not constantly executing. Sometimes it has to wait for a specific event to happen before it can proceed. For example, if Oracle (or the SQL statement) wants to modify data, and the corresponding database block is not currently in the SGA, Oracle waits for this block to be available for modification. The Waiting time refers to the time spent by the Oracle server waiting for such events to complete. Oracle has a bunch of events that it can wait for - eg., buffer busy waits, db file scattered read, db file sequential read.

Whenever users complaint of a slowdown while accessing databases in a cluster, it would be helpful to know which node is experiencing a slowdown and where it is spending too much time - is the time executing more than the time spent waiting, or vice-versa? To determine this, you should monitor both the CPU time and the Waiting time of each node of the cluster. This test enables you to perform ‘half’ this analysis. In other words, this test reports the percentage of time that every node spent on waiting for one/more events to complete. This way, the test helps you understand whether/not the waiting time is contributing to the poor responsiveness of the cluster service and which node has been waiting too long.

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 Cluster

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 RAC, a special database user account has to be 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

DB time spent waiting:

Indicates the percentage of time this node spent on waiting for one/more events to complete.

Percent

A high value is indicative of the following cases:

  • An increase in load (either more users, more calls, or larger transactions)
  • I/O performance degradation (I/O time increases and wait time increases, so DB time increases)
  • Application performance degradation
  • CPU-bound host (foregrounds accumulate active run-queue time, wait event times are artificially inflated)