Managing Application Workloads with Database Services

About Database Services

Database services (services) are logical abstractions for managing workloads in Oracle Database. Services divide workloads into mutually disjoint groupings. Each service represents a workload with common attributes, service-level thresholds, and priorities. The grouping is based on attributes of work that might include the application function to be used, the priority of execution for the application function, the job class to be managed, or the data range used in the application function or job class. For example, the Oracle E-Business suite defines a service for each responsibility, such as general ledger, accounts receivable, order entry, and so on. When you configure database services, you give each service a unique global name, associated performance goals, and associated importance. The services are tightly integrated with Oracle Database and are maintained in the data dictionary.

Connection requests can include a database service name. Thus, middle-tier applications and client-server applications use a service by specifying the service as part of the connection in TNS connect data. If no service name is included and the Net Services file listener.ora designates a default service, the connection uses the default service.

Services enable you to configure a workload, administer it, enable and disable it, and measure the workload as a single entity. You can do this using standard tools such as the Database Configuration Assistant (DBCA), Net Configuration Assistant (NetCA), and Enterprise Manager (EM). Enterprise Manager supports viewing and operating services as a whole, with drill down to the instance-level when needed.

In an Oracle Real Application Clusters (Oracle RAC) environment, a service can span one or more instances and facilitate workload balancing based on transaction performance. This provides end-to-end unattended recovery, rolling changes by workload, and full location transparency. Oracle RAC also enables you to manage a number of service features with Enterprise Manager, the DBCA, and the Server Control utility (SRVCTL).

Services also offer an extra dimension in performance tuning. Tuning by "service and SQL" can replace tuning by "session and SQL" in the majority of systems where all sessions are anonymous and shared. With services, workloads are visible and measurable. Resource consumption and waits are attributable by application. Additionally, resources assigned to services can be augmented when loads increase or decrease. This dynamic resource allocation enables a cost-effective solution for meeting demands as they occur. For example, services are measured automatically and the performance is compared to service-level thresholds. Performance violations are reported to Enterprise Manager, enabling the execution of automatic or scheduled solutions.

Several Oracle Database features support services. The Automatic Workload Repository (AWR) manages the performance of services. AWR records service performance, including execution times, wait classes, and resources consumed by service. AWR alerts warn when service response time thresholds are exceeded. The dynamic views report current service performance metrics with one hour of history. Each service has quality-of-service thresholds for response time and CPU consumption.

In addition, the Database Resource Manager can map services to consumer groups. This enables you to automatically manage the priority of one service relative to others. You can use consumer groups to define relative priority in terms of either ratios or resource consumption. This is described in more detail in Chapter 26, "Managing Resource Allocation with Oracle Database Resource Manager," and specifically in "Specifying Session-to–Consumer Group Mapping Rules".

Services describe applications, application functions, and data ranges as either functional services or data-dependent services. Functional services are the most common mapping of workloads. Sessions using a particular function are grouped together. In contrast, data-dependent routing routes sessions to services based on data keys. The mapping of work requests to services occurs in the object relational mapping layer for application servers and TP monitors. For example, in Oracle RAC, these ranges can be completely dynamic and based on demand because the database is shared.

You can also define preconnect application services in Oracle RAC databases. Preconnect services span instances to support a service in the event of a failure. The preconnect service supports TAF preconnect mode and is managed transparently when using RAC.

In addition to services to be used by applications, Oracle Database also supports two internal services: SYS$BACKGROUND is used by the background processes only and SYS$USERS is the default service for user sessions that are not associated with services.

Using services requires no changes to your application code. Client-side work can connect to a named service. Server-side work, such as Oracle Scheduler, parallel execution, and Oracle Streams Advanced Queuing, set the service name as part of the workload definition. Work requests executing under a service inherit the performance thresholds for the service and are measured as part of the service.

For Oracle Scheduler, you optionally assign a service when you create a job class. During execution, jobs are assigned to job classes, and job classes can run within services. Using services with job classes ensures that the work executed by the job scheduler is identified for workload management and performance tuning.

For parallel query and parallel DML, the query coordinator connects to a service just like any other client. The parallel query processes inherit the service for the duration of the execution. At the end of query execution, the parallel execution processes revert to the default service.

Creating Database Services

There are a few ways to create database services, depending on your database configuration.

To create a database service:

1. If your single-instance database is being managed by Oracle Restart, use the SRVCTL utility to create the database service.

   srvctl add service -d db_unique_name -s service_name
   

2. If your single-instance database is not being managed by Oracle Restart, do one of the following:

   • Append the desired service name to the SERVICE_NAMES parameter.

   • Call the DBMS_SERVICE.CREATE_SERVICE package procedure.

3. (Optional) Define service attributes with Oracle Enterprise Manager or with DBMS_SERVICE.MODIFY_SERVICE.

Database Service Data Dictionary Views

You can find service information in the following service-specific views:

• DBA_SERVICES

• ALL_SERVICES or V$SERVICES

• V$ACTIVE_SERVICES

• V$SERVICE_STATS

• V$SERVICE_EVENTS

• V$SERVICE_WAIT_CLASSES

• V$SERV_MOD_ACT_STATS

• V$SERVICE_METRICS

• V$SERVICE_METRICS_HISTORY

The following additional views also contain some information about services:

• V$SESSION

• V$ACTIVE_SESSION_HISTORY

• DBA_RSRC_GROUP_MAPPINGS

• DBA_SCHEDULER_JOB_CLASSES

• DBA_THRESHOLDS