Shulou(Shulou.com)06/01 Report--

Concept

Proprietary connection: responds to a client request with a server process.

Shared connection: in shared server mode, after the client connects to the dispatcher through listening, the dispatcher randomly assigns a port. At this time, the client disconnects and monitors the connection. Through the assigned port and dispatcher connection, the connection to the listening is short-lived.

Applicable scenario

For applications with a small number of connections, it is appropriate to use proprietary connections, and the customer's request response is timely.

For applications with a large number of connections, it is appropriate to use shared connections to make full use of system resources.

General parameter

Remote_listener: you can separate the database from the listener.

The remote_listener for a stand-alone environment is generally empty.

In the rac environment, listener is started with the cluster crs. And the database. The startup of rdbms depends on the resources of the asm instance, so after starting the database, listener does not start, except for failure.

Local_listener is the listener information of this node

Remote_listener is usually the information of scan

Local_listener

Pmon will only dynamically register listeners whose port is equal to 1521, otherwise pmon cannot dynamically register listener. If you want pmon to register listener dynamically, you need to set the local_listener parameter.

Listener_networks: it is necessary to configure multiple remote_listener and local_listener, but it is rarely used.

Example: alter system set LISTENER_NETWORKS=' ((NAME=network1) (LOCAL_LISTENER=listener_net1) (REMOTE_LISTENER=scanone.gaopp.com:1521))','((NAME=network2) (LOCAL_LISTENER=listener_net2) (REMOTE_LISTENER=remote_net2))'

Shared parameter

SHARED_SERVERS: if the shared_server value is 0, the database does not start shared services mode. This parameter is required to configure shared server, and only this parameter is required. It specifies the number of shared server process starts when the instance starts. Do not set this parameter too large, otherwise it will take more time to start the database instance. After Oracle starts, the shared_servers will be dynamically adjusted according to the load.

The maximum shared server process that MAX_SHARED_SERVERS:Oracle can use at the same time. Do not set this parameter less than shared_servers, if you dynamically modify shared_servers greater than max_shared_servers,oracle will overwrite the value of max_shared_servers, you need to modify max_shared_servers. At the same time, it cannot be greater than processes. This parameter is set for resource-intensive operations (batch), in order to reserve some process for DBA tasks (rman backups).

SHARED_SERVER_SESSIONS: specifies the total number of shared server session allowed. If this parameter is set, do not exceed the value of sessions. If this value is not set, as long as there is free session, it can be used. Setting this value is the User Sessions reserved for dedicated connections.

DISPATCHERS: the number of dispatchers sharing the connection.

MAX_DISPATCHERS: the maximum number of dispatchers that can be shared concurrently. This parameter is currently negligible.

CIRCUITS: number of virtual loops available (Specifies the total number of virtual circuits that are available for inbound and outbound network sessions)

Memory

Large_pool_size

Compared with the dedicated server mode, the UGA of the shared service mode is in SGA, while the UGA of the dedicated server mode is in PGA. If large_pool_size is set in the shared server mode, the user's UGA will be in large_pool. The memory reduced by MTS is actually the memory needed for each user to connect to the operating system process in the dedicated server mode. The shared server mode limits the number of Server Process, reduces the memory needed to establish Server Process, and does not need to create and delete processes frequently when the concurrency is large, which reduces the corresponding overhead and improves the concurrency. Therefore, the shared server mode is suitable for business systems with high concurrency and small processing capacity.

Process

After the database is started, there are two more processes than the dedicated server mode, one is the scheduling process (Dnnn), and the other is the shared server process (Snnn). The request from the client is accepted by the dispatcher, and the dispatcher places the request into the Request queue. The idle Server Process starts processing requests in the queue according to the request queue. The processed results are put into the Response queue. Finally, DIspatcher returns the final result to the client.

Snnn: the dispatcher process enables client processes to share a limited number of server processes. You can create multiple dispatcher processes for a single database instance. The optimal number of dispatcher processes depends on the operating system limit and the number of connections per process.

Dnnn: in a shared server configuration, each shared server process serves multiple client requests. Shared server processes and dedicated server processes provide the same functionality except that shared server processes are not associated with specific client processes.

Advantages:

Reduces the number of processes in the instance

Increased the number of more concurrent users

Realize dynamic load balancing

Reduced the number of idle server processes

Reduced instance PGA memory

Disadvantages: because there are all kinds of problems in the shared server mode, and the middleware can also achieve the effect of connection pooling, so in general, it will not share the server mode, just use the dedicated server mode.

The code path of a shared server is longer than that of a dedicated server, so it is inherently slower than a dedicated server.

There is the possibility of artificial deadlock because it is serial, and as long as a connection is blocked, all users on the server process are blocked and are most likely deadlocked.

There is the possibility of exclusive transactions, because if a session's transaction runs for too long, it monopolizes shared resources, other users can only wait, while dedicated servers, each client is a session.

The shared server mode limits certain database features, such as the inability to start and shut down instances separately, media recovery, the use of Log Miner, and SQL_TRACE is meaningless (because it is shared rather than the current session).

Event

Event 10257 (more on later)

View

V$DISPATCHER: provides DISPATCH process information, including DISPATCH name, network, address, status, statistics, index number, etc.

It is recorded that the dispatchers parameter is configured.

V$DISPATCHER_CONFIG: provides configuration information for DISPATCH

V$DISPATCHER_RATE: provides RATE statistics for DISPATCH

V$CIRCUIT: provides virtual loop information (virtual circuits) for users to connect to the database through DISPATCH

There are records indicating that there is a connection using shared mode. If there is no record, the server mode cannot be determined.

V$SHARED_SERVER: provides shared server information

If there is a record, and the STATUS field is WAIT (COMMON), it means sharing is started.

No record, or the STATUS field is TERMINATED, which means the shared server is not started

V$SHARED_SERVER_MONITOR: provides optimization information for shared servers

V$QUEUE: provides shared server queue information.

V$SESSION: if the value of the SERVER field includes DEDICATED and NONE, the current instance starts the shared server, and the session whose SERVER is NONE is using the shared server to connect. At the same time, if only DEDICATED is displayed, it does not mean that the server must be working under the dedicated server, and it is possible to start the sharing mode. It's just that currently all connections to the database are in dedicated server mode.

Turn off database sharing mode

You only need to set the parameter shared_servers to 0 to turn off the shared mode of the database. After the script is executed, all shared connections to the database will not succeed, but unreleased shared connections will remain connected until disconnected. Alter system set shared_servers=0; if both the parameters shared_servers and max_shared_servers are set to 0, then the shared connection mode will be terminated. All shared connections will be disconnected (already connected sessions will also be disconnected) to turn on database sharing mode

Set the parameter shared_servers and set its value to greater than 0 to turn on server sharing mode. Other shared server parameters do not need to be set, but it is best to set the max_shared_servers parameter as well

Alter system set shared_servers=1 scope=both;alter system set max_shared_servers = 24 scope=both; for the setting of the parameter dispatchers, you can use the following command alter system set dispatchers=' (protocol=TCP) (disp=8) (serv=xxx)'to indicate the protocol, disp represents the number of processes in the dipatcher, and service specifies the name of the service to be in shared server mode respectively. Use the above mode to specify the shared mode in which only a service is started. If you want to set all services to use the shared mode, set it to: alter system set dispatchers=' (PROTOCOL=TCP)'; judgment of the current mode

1. View the V$SESSION view

The current connection mode is further determined by the SERVER field of the V$session view.

two。 View the tns configuration file for connecting to the database, as shown below

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