Usage and Configuration of Oracle Shared Server // Database Administration
Usage and Configuration of Oracle Shared Server
Oracle Shared Server is a feature of Oracle Database that allows multiple users to share a single set of server resources. This architecture is particularly beneficial in environments with many concurrent users, helping to optimize resource utilization and improve scalability. Here’s a comprehensive overview of its usage and configuration.
---
1. Understanding Oracle Shared Server Architecture
#### 1.1. Key Concepts
**Dedicated Server vs. Shared Server**:
In a *dedicated server* configuration, each user session has its own server process, which can lead to high resource consumption with many concurrent users.
In a *shared server* configuration, multiple user sessions share a pool of server processes, allowing for more efficient resource management.
**Dispatcher**: The process that manages the incoming user requests and directs them to the appropriate shared server processes.
**Shared Server Process**: A server process that handles requests from multiple client sessions.
#### 1.2. Benefits
**Resource Efficiency**: Reduces the number of server processes required, conserving memory and CPU resources.
**Scalability**: Allows the database to support a larger number of users without a proportional increase in server resources.
**Cost-Effectiveness**: Ideal for environments with a high number of short-lived sessions.
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2. Configuring Oracle Shared Server
To configure Oracle Shared Server, you need to make specific adjustments in the database initialization parameters and create necessary components.
#### 2.1. Initialization Parameters
Modify the database initialization parameters in your `init.ora` or `spfile` configuration file. The key parameters include:
**DISPATCHERS**: Specifies the number of dispatcher processes and their configurations.
```plaintext
DISPATCHERS='(PROTOCOL=TCP)(DISPATCHERS=3)'
```
**SHARED_SERVERS**: Specifies the number of shared server processes available to handle user requests.
```plaintext
SHARED_SERVERS=10
```
**MAX_SHARED_SERVERS**: Sets the maximum number of shared server processes that can be started.
```plaintext
MAX_SHARED_SERVERS=50
```
**SESSION_CACHED_CURSORS**: Determines how many cursors can be cached in the shared server.
```plaintext
SESSION_CACHED_CURSORS=50
```
#### 2.2. Enabling Shared Server Mode
1. **Set Initialization Parameters**: As mentioned above, configure the parameters in the database’s initialization file.
2. **Restart the Database**: After modifying the initialization parameters, restart the Oracle instance for the changes to take effect.
3. **Verify Configuration**: Use the following SQL commands to confirm that the shared server is configured correctly:
```sql
SHOW PARAMETER DISPATCHERS;
SHOW PARAMETER SHARED_SERVERS;
```
---
3. Creating and Managing Dispatchers
Oracle provides flexibility in configuring dispatchers to optimize performance based on your needs.
#### 3.1. Configuring Multiple Dispatchers
You can configure multiple dispatchers for different protocols or settings:
```plaintext
DISPATCHERS='(PROTOCOL=TCP)(DISPATCHERS=3),(PROTOCOL=IPC)(DISPATCHERS=2)'
```
#### 3.2. Dynamic Dispatcher Configuration
You can dynamically add dispatchers without restarting the database using:
```sql
EXEC DBMS_DISPATCHER.ADD_DISPATCHER('PROTOCOL=TCP');
```
---
4. Connecting to Shared Server
Client applications need to connect to the shared server configuration explicitly. The connection string may look like this for Oracle Net:
```plaintext
CONNECT username/password@//hostname:port/service_name
```
The connection string does not need any special configuration to indicate that it is using shared servers; Oracle will automatically route the connection appropriately.
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5. Monitoring Shared Server
Monitoring is essential to ensure optimal performance. You can use various views to monitor the shared server processes and dispatchers.
#### 5.1. Key Views
**V$DISPATCHER**: Displays information about dispatcher processes.
```sql
SELECT * FROM V$DISPATCHER;
```
**V$SHARED_SERVER**: Provides information about shared server processes.
```sql
SELECT * FROM V$SHARED_SERVER;
```
**V$SESSION**: Shows the session information, including whether a session is using a shared server.
```sql
SELECT SID, SERIAL#, SERVER FROM V$SESSION WHERE SERVER='SHARED';
```
#### 5.2. Performance Metrics
Monitor metrics such as response times, number of requests processed, and resource utilization to optimize configuration.
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6. Best Practices
1. **Monitor Resource Usage**: Regularly monitor shared server usage to adjust the number of processes based on actual load.
2. **Adjust Dispatcher Configurations**: Optimize dispatcher configurations based on your application’s needs (e.g., different protocols or different load patterns).
