Oracle RAC Checkpoint Events Test

The checkpoint process is responsible for updating file headers in the database datafiles. A checkpoint occurs when Oracle moves new or updated blocks (called dirty blocks) from the RAM buffer cache to the database datafiles. A checkpoint keeps the database buffer cache and the database datafiles synchronized. This synchronization is part of the mechanism that Oracle uses to ensure that your database can always be recovered.

Check-pointing is an important Oracle activity which records the highest system change number (SCN), so that all data blocks less than or equal to the SCN are known to be written out to the data files. If there is a failure and then subsequent cache recovery, only the redo records containing changes at SCN(s) higher than the checkpoint need to be applied during recovery.

Key checkpoint-related activities may generate wait events. For instance, SQL statements may have to wait for processing until the DBWR (database writer) finishes writing dirty blocks in the buffer cache to the datafiles. If too many such wait events occur on an instance, it may cause the performance of the Oracle cluster to deteriorate. It is hence essential to keep close tabs on the checkpoint-related wait events and the activity responsible for them. 

The Oracle RAC Checkpoint Events test auto-discovers the wait event types related to the checkpoint process, and reports the number of events of each type that have occured in each instance of an Oracle RAC. 

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 RAC as 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 agent

Outputs of the test : One set of results for every wait event type discovered on each instance of the monitored 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. SCAN Name - SCAN stands for Single Client Access Name, it is a feature used in Oracle RAC environments that provide a single name for clients to access any Oracle Database running in the cluster. You can provide SCAN as an alternative to IP/Host Name. If this parameter value is provided, it will be used for connectivity otherwise IP/Hostname will be used.
  5. orasid - The variable name of the oracle instance.

  6. 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’

  7. 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.

  8. Password – Password of the specified database user
  9. Confirm password – Confirm the password by retyping it here.
  10. SSL- By default, this flag is set to No, as the target Oracle cluster is not SSL-enabled by default. If the target cluster is SSL-enabled, then set this flag to Yes.
  11. SSL Cipher-This parameter is applicable only if the target Oracle Cluster is SSL-enabled, if not, set this parameter to none. A cipher suite is a set of cryptographic algorithms that are used before a client application and server exchange information over an SSL/TLS connection. It consist of sets of instructions on how to secure a network through SSL (Secure Sockets Layer) or TLS (Transport Layer Security). In this text box, provide a comma-seperated list of cipher suites that are allowed for SSL/TLS connection to the target cluster. By default, this parameter is set to none.
  12. TRUSTSTORE FILE- This parameter is applicable only if the target Oracle Cluster is SSL-enabled, if not, set this parameter to none. TrustStore is used to store certificates from Certified Authorities (CA) that verify and authenticate the certificate presented by the server in an SSL connection. Therefore, the eG agent should have access to the truststore where the certificates are stored to authenticate and connect with the target cluster and collect metrics. For this, first import the certificates into the following default location <eG_INSTALL_DIR>/lib/security/mytruststore.jks. To know how to import the certificate into the truststore, refer toPre-requisites for monitoring Oracle Cluster. Then, provide the truststore file name in this text box. For example: mytruststore.jks. By default, none is specified against this text box.
  13. TRUSTSTORE TYPE-This parameter is applicable only if the target Oracle Cluster is SSL-enabled, if not, set this parameter to none.Specify the type of truststore that contains the certificates for server authentication in this text box. For eg.,JKS. By default, this parameter is set to the value none.
  14. TRUSSTORE PASSWORD-This parameter is applicable only if the target Oracle Cluster is SSL-enabled, if not, set this parameter to none. If a Truststore File name is provided, then, in this text box, provide the password that is used to obtain the associated certificate details from the Truststore File. By default, this parameter is set to none.

  15. 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

Event Count

Indicates the number of wait events of this type that have occurred on this instance during the last measurement period.

Number

Ideally, the value of this measure should be low. A consistent increase in this value is a cause of concern, as it indicates that a checkpoint-related activity is not getting completed, resulting in the generation of numerous wait events and degrading the overall performance of the Oracle RAC. 

Compare the value of this measure across the event types to determine which type of wait event has occurred most frequently on an instance.