The shared server architecture enables a database server to allow many user processes to share very few server processes, so the number of users that can be supported is increased. With shared server, many user processes connect to a dispatcher. The dispatcher directs multiple incoming network session requests to a common queue. An idle shared server process from a shared pool of server processes picks up a request from the queue. This means a small pool of server processes can serve a large number of clients.
This chapter describes how to configure dispatcher. It contains these topics:
See Also:Oracle9i Database Administrator's Guide for further information about shared server configuration
Shared memory resources for dispatchers, virtual circuits, and shared servers are preconfigured to allow the enabling of shared servers at runtime. Database administrators can start dispatchers and shared servers with the SQL
ALTER SYSTEM statement without having to restart the instance to start shared servers. A dispatcher is started automatically on the TCP/IP protocol when shared server mode is turned on and the dispatchers parameterhas not been set. The default configuration for the dispatcher is equivalent to the following
DISPATCHERS parameter setting in the database initialization parameter file.
In configurations in which client load is causing a strain on memory and other system resources, database administrators can remedy load issues by starting shared server resources.
DISPATCHERS parameter if either of the following conditions apply:
ADDRESS (ADD or ADDR)
DESCRIPTION (DES or DESC)
PROTOCOL (PRO or PROT)
After setting this parameter, you do not need to restart the instance. You can alter dispatchers configurations with the SQL statement ALTER SYSTEM.
Note:Database Configuration Assistant enables you to configure the
Oracle Database Administrator's Guide for further information about shared server configuration
Oracle Database Reference for further information about configuring the
DISPATCHERS parameter and supported attributes
Oracle Database SQL Reference for further information about the
Connection pooling is a resource utilization feature that enables you to reduce the number of physical network connections to a dispatcher. This is achieved by sharing or pooling a set of connections among the client processes.
Consider a system that can support 950 connections for each process and has:
4000 users concurrently connected through TCP/IP
2,500 sessions concurrently connected through TCP/IP with SSL
In this case, the
DISPATCHERS attribute for TCP/IP should be set to a minimum of five dispatchers and TCP/IP with SSL should be set to three dispatchers:
Connection pooling can allow each dispatcher to handle more than 950 sessions. For example, suppose that clients are idle most of the time and one dispatcher can route requests and responses for 4000 TCP/IP sessions, or 2,500 TCP/IP with SSL sessions. The following configuration reduces the number of dispatchers required to one for each protocol and allows the dispatchers to be more fully utilized:
DISPATCHERS="(PROTOCOL=tcp)(DISPATCHERS=1)(POOL=on)(TICK=1) (CONNECTIONS=950)(SESSIONS=4000)" DISPATCHERS="(PROTOCOL=tcps)(DISPATCHERS=1)(POOL=on)(TICK=1) (CONNECTIONS=950)(SESSIONS=2500)"
The DISPATCHERS and CONNECTIONS attributes do not have to be specified, since the default for DISPATCHERS is 1 and the default for CONNECTIONS is the maximum number of connections for each process, which is operating system dependent.
See Also:"Connection Pooling"
Session multiplexing, available with Oracle Connection Manager, enables multiple client sessions to funnel through a single protocol connection. For example, several user processes can connect to one dispatcher by way of a single connection from Oracle Connection Manager.
Oracle Connection Manager communicates from users to the dispatcher by way of a shared connection. At any one time, zero, one, or a few users might need the connection, while other user processes linked to the dispatcher by way of the connection manager process are idle. This way, session multiplexing is beneficial because it maximizes use of the dispatcher process connections.
Session multiplexing is also useful for multiplexing database link sessions between dispatchers. The limit on the number of sessions for each dispatcher is operating system specific.
To enable session multiplexing, simply set attribute
MULTIPLEX in the
DISPATCHERS parameter to on or to an equivalent value.
An Oracle database can be represented by multiple service names. Because of this, a pool of dispatchers can be allocated exclusively for clients requesting a particular service. This way, the mission critical requests may be given more resources and, thus, in effect increase their priority.
For example, the following initialization parameter file sample shows two dispatchers. The first dispatcher services requests for clients requesting
sales.us.acme.com. The other dispatcher services requests only for clients requesting
SERVICE_NAMES=sales.us.acme.com INSTANCE_NAME=sales DISPATCHERS="(PROTOCOL=tcp)" DISPATCHERS="(PROTOCOL=tcp)(SERVICE=adminsales.us.acme.com)"
If shared server is configured and a client connection request arrives when no dispatchers are registered, then the request is processed by a dedicated server process. If you want a particular client always to use a dispatcher, configure
=shared) in the
CONNECT_DATA section of the connect descriptor. For example:
sales= (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)) (CONNECT_DATA= (SERVICE_NAME=sales.us.acme.com) (SERVER=shared)))
If a dispatcher is not available, then the client connection request is rejected.
See Also:"Configuring Advanced Connect Data Parameters" to set the
If the database is configured for shared server and a particular client requires a dedicated server, you can configure the client to use a dedicated server in one of the following ways:
You can configure a net service name with a connect descriptor that contains
=dedicated) in the
CONNECT_DATA section. For example:
sales= (DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)) (CONNECT_DATA= (SERVICE_NAME=sales.us.acme.com) (SERVER=dedicated)))
You can configure the client profile (
sqlnet.ora file) with
USE_DEDICATED_SERVER=on. This adds
=dedicated) to the
CONNECT_DATA section of the connect descriptor the client uses.
USE_DEDICATED_SERVERis set to
ON, then existing
)entries in connect descriptors are overwritten with