Oracle RAC Root Blockers Test

One common problem encountered with databases is blocking. Suppose that process A is modifying data that process B wants to use. Process B will be blocked until process A has completed what it is doing. This is only one type of blocking situation; others exist and are common. What matters to a database administrator is identifying when blocking is a problem and how to deal with it effectively. When blocking is bad enough, users will notice slowdowns and complain about it. With a large number of users, it is common for tens or hundreds of processes to be blocked when slowdowns are noticed. Killing these processes may or may not solve the problem because 10 processes may be blocked by process B, while process B itself is blocked by process A. Issuing 10 kill statements for the processes blocked by B probably will not help, as new processes will simply become blocked by B. Killing process B may or may not help, because then the next process that was blocked by B, which is given execution time, may get blocked by process A and become the process that is blocking the other 9 remaining processes. When you have lots of blocking that is not resolving in a reasonable amount of time you need to identify the root blocker, or the process at the top of the tree of blocked processes. Imagine again that you have 10 processes blocked by process B, and process B is blocked by process A. If A is not blocked by anything, but is itself responsible for lots of blocking (B and the 10 processes waiting on B), then A would be the root blocker. (Think of it as a traffic jam. Figure 1 will help) Killing A (via kill) is likely to unblock B, and once B completes, the 10 processes waiting on B are also likely to complete successfully.

The Oracle RAC Root Blockers test reports the number of root blocker processes in the clustered database. The detailed diagnosis of this test, provides the details of each of these blocker processes, thereby enabling you to identify the root blocker. 

Figure 1 : The traffic jam analogy representing blocking

Target of the test : Oracle Server

Agent deploying the test : An internal agent

Outputs of the test : One set of results for the Oracle cluster monitored.

Configurable parameters for the test

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 orasid - The variable name of the oracle instance 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’ 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. Password – Password of the specified database user Confirm password – Confirm the password by retyping it here. 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. 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. 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. 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. 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.

Measurements made by the test

Measurement	Description	Measurement Unit	Interpretation
Root blockers:	Indicates the number of root blocker processes.	Number	If this value increases suddenly, this is a cause for concern. Likewise, if a process has been blocking other processes for a long time, it is a reason for further investigation. The detailed diagnosis for this test, if enabled, will indicate which process is blocking which other processes. Killing a blocker process that has been running for a long while may get the database running well again. Also, by carefully observing the details of the blocker processes, you can quickly identify the root blocker, and investigate the reason why it is blocking other processes.
Max blocking time	Indicates the maximum time for which a process blocked one/more processes.	Seconds	eG Enterprise isolates processes that have been blocking other processes for a duration greater than the configured MAX BLOCKING TIME. The blocking time of these processes is then compared and the maximum blocking time is identified and reported as the value of this measure. If this time is abnormally high, it indicates that a process been blocking resource access to other process(es) for a very long time. Prolonged blocking can significantly degrade database performance. Under such circumstances therefore, you can use the detailed diagnosis of the Blocked sessions measure to know which process was blocked for the maximum time and by which process.
Blocked sessions	Indicates the number of sessions that are blocked currently.	Number	Ideally, the value of this measure should be low. A consistent increase in this value is a cause for concern.