Oracle RAC Transaction Workload Test

Knowing the count of transactions executing on each node/instance of the Oracle cluster per second can indicate the transaction load on the node in an Oracle cluster. However, the true impact of this load can be assessed and understood only if administrators are enabled to determine the number and type of database operations each transaction triggers. This is where the Oracle RAC Transaction Workload test helps! This test reports how many key database operations - e.g., data modifications, block changes, reads/writes, parses, rollbacks, etc. - are performed on the server per transaction. This way, the test reveals the real workload of the server. In addition, the test also enables administrators to compare current CPU usage with the real workload, so that they can figure out whether/not the server needs to be resized to handle its load.

Target of the test : Oracle RAC

Agent deploying the test : An internal agent

Outputs of the test : One set of results for every node in the Oracle cluster

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

Redo size

Indicates the amount of data written to the redo logs per transaction since the last measurement period.

MB/Trans

If the value of this measure keeps growing, it could indicate that transactions are making numerous and frequent changes to the data in the databases.

 Logical reads

Indicates the number of logical reads performed by the server per transaction.

Reads/Trans

These measures are good indicators of the level of activity that every transaction generated on the database server.

Block changes

Indicates the number of database blocks that were changed per transaction.

Blocks/Trans

Physical reads:

Indicates the number of physical reads performed per transaction.

Reads/Trans

Physical writes

Indicates the number of physical writes performed per transaction.

Writes/Trans

User calls

Indicates the number of user calls made per transaction.

Calls/Trans

 

Parses

Indicates the number of parses executed by the server per transaction.

Parses/Trans

Parsing is one stage in the processing of a SQL statement. When an application issues a SQL statement, the application makes a parse call to Oracle Database. During the parse call, Oracle Database:

  • Checks the statement for syntactic and semantic validity.
  • Determines whether the process issuing the statement has privileges to run it.
  • Allocates a private SQL area for the statement.

If the value of this measure keeps increasing consistently, it could indicate on an average, transactions are executing many SQL statements on the server, thus generating more parses. 

 Hard parses:

Indicates the number of hard parses executed per transaction.

Parses/Trans

As opposed to a soft parse, a hard parse loads the SQL source code into RAM for parsing. A high value for this measure therefore indicates that the server is performing many hard parses.  

WA memory processed

Indicates the amount of work area memory used up by the server per transaction.

MB/Trans

Oracle Database reads and writes information in the PGA on behalf of the server process. An example of such information is the run-time area of a cursor. Each time a cursor is executed, a new run-time area is created for that cursor in the PGA memory region of the server process executing that cursor. For complex queries (such as decision support queries), a big portion of the run-time area is dedicated to work areas allocated by memory intensive operators, including:

  • Sort-based operators, such as ORDER BY, GROUP BY, ROLLUP, and window functions
  • Hash-join
  • Bitmap merge
  • Bitmap create
  • Write buffers used by bulk load operations

For example, a sort operator uses a work area (sometimes called the sort area) to perform the in-memory sort of a set of rows. Similarly, a hash-join operator uses a work area (also called the hash area) to build a hash table from its left input. If the amount of data to be processed by these two operators does not fit into a work area, then the input data is divided into smaller pieces. This allows some data pieces to be processed in memory while the rest are spilled to temporary disk storage to be processed later. 

A consistent increase in the value of this measure is indicative of excessive usage of the work area by transactions. This could indicate that the transaction workload is characterized by complex queries that use memory intensive operators such as sort, hash-join, etc. You may want to fine-tune the work area size in order to enable it to handle the memory-intensive load better.

Logons

Indicates the number of users logging in per transaction.

Logons/Trans

A steady rise in this value is indicative of a steady increase in user activity on the server.

Executes

Indicates the number of executes performed per transaction.

Executions/Trans

 

Rollbacks

Indicates the number of rollbacks performed per transaction.

Rollbacks/Trans

Ideally, the value of this measure should be low. This is because, rollbacks are expensive operations and should be avoided at all costs. A consistent increase in the value of this measure is hence a cause for concern.