DEDICATED SERVER & SHARED SERVER - - Get a Free Blog

DEDICATED SERVER

& SHARED SERVER

Prepared By: L. Huyam Al-Amro

LECTURE 4

SERVER PROCESS

Server process: Gets requests from the user process

and interacts with the oracle instance to carry out

the requests:

Parsing and executing SQL statement via the

application or tool.

Reading the data files and bringing data blocks

into the buffer cache.

Returning the results to the user process in such a

way that it can understand the data.


USER PROCESS

User process:

It is started when the user run the application tool

(application program or oracle tool).

It may be on the same machine where the

instance/database resides, or it may be initiated

from a client machine in a client/server

architecture.


DEDICATED SERVER CONFIGURATION



One server process is created for each connectionrequest.

1. The client application or tool initiates the userprocess to connect to the instance.

2. The client machine communicates the request to theserver machine by using Oracle Net Drivers. TheOracle Net Listener on the server detects therequest and starts (create) a dedicated serverprocess after verifying the user name andpassword.



3. The user issues a SQL command.

4. The dedicated server process determines whether

a similar SQL is in the shared SQL area. If not, it

allocates a new shared SQL area for the

command and stores the parse tree.

5. During parsing, the server process checks for

syntactic correctness of the statement, checks

whether the object names are valid, and

privileges.



The required information is obtained from the data

dictionary cache. A PGA is created to store the

private information of the process.

6. The server process looks for data blocks that need

to be changed or accessed in the buffer cache. If

they are not there, it reads the data files and

brings the necessary blocks to the SGA.

7. The server process executes the SQL statement.



8. If data blocks need to be changed, they are

changed in the buffer cache (the DBWn process

updates the data file). The change is logged in the

redo log buffer.

9. The result is returned to the User process.


SHARED SERVER CONFIGURATION




One server process manage multiple user processes.

1. When the instance is started, one or more shared

server processes and dispatcher processes are

started. The OracleNet Listener is running on the

server. The request and response queues are

created in the SGA.

2. The client application or tool initiates the user

process to connect to the instance.



3. The client machine communicates the request to the

server machine by using OracleNet drivers. The

OracleNet Listener on the server detects the

request and identifies the protocol that the user

process is running. It connects the user process to

one of the dispatchers for this protocol (if no

dispatcher is avaliable for the requested protocol,

a dedicated server process is started by the

listener).



4. The user issues a SQL command.

5. The dispatcher decodes the request and puts it

into the request queue (at the tail) along with the

dispatcher ID.

6. The request moves up the queue as the server

processes serve the previous requests. The next

available shared server process picks up the

request.



7. The shared server process determines whether a

similar SQL statement is in the shared SQL area. If

not, it allocates a new shared SQL area for the

command and stores the parse tree.

8. After SQL execution, the shared server process

places the result in the response queue along with

the dispatcher ID.



9. The result is returned to the User process by the

dispatcher process.

DIFFERENCE BETWEEN DEDICATED

SERVER & SHARED SERVER


EXAMPLE OF MEMORY USAGE FOR

DEDICATED SERVER & SHARED SERVER


Consider an application in which the memory required

for each session is 400 KB and the memory required for

each server process is 4 MB. The pool size is 100 and

the number of shared servers used is 100.

If there are 5000 client connections, the memory used

by each configuration is as follows:

EXAMPLE OF MEMORY USAGE FOR

DEDICATED SERVER & SHARED SERVER


Dedicated Server

Memory used = 5000 X (400 KB + 4 MB) = 22 GB

Shared Server

Memory used = 5000 X 400 KB + 100 X 4 MB = 2.5

GB

CONFIGURING ORACLE DATABASE FOR

SHARED SERVER


Initialization Parameters for Shared Server:

The following initialization parameters control shared server operation:

■ SHARED_SERVERS: Specifies the initial number of shared servers to start and the minimum number of shared servers to keep. This is the only required parameter for using shared servers.

■ MAX_SHARED_SERVERS: Specifies the maximum number of shared servers that can run simultaneously.

CONFIGURING ORACLE DATABASE FOR

SHARED SERVER


■ SHARED_SERVER_SESSIONS: Specifies the total

number of shared server user sessions that can run

simultaneously. Setting this parameter enables you

to reserve user sessions for dedicated servers.

■ DISPATCHERS: Configures dispatcher processes in

the shared server architecture.

■ MAX_DISPATCHERS: Specifies the maximum

number of dispatcher processes that can run

simultaneously.

ENABLING SHARED SERVER


Shared server is enabled by setting the

SHARED_SERVERS initialization parameter to a

value greater than 0.

If SHARED_SERVERS is not included in the

initialization parameter file at database startup,

but DISPATCHERS is included and it specifies at

least one dispatcher, shared server is enabled. In

this case, the default for SHARED_SERVERS is 1.

ENABLING SHARED SERVER


Shared server can be started dynamically by

setting the SHARED_SERVERS parameter to a

nonzero value with the ALTER SYSTEM statement.

Example: ALTER SYSTEM SET SHARED_SERVERS = 5;

If SHARED_SERVERS is not included in the

initialization parameter file, or is included but is set

to 0, then shared server is not enabled at database

startup.

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