Oracle Dedicated server 和 Shared server（专用模式 和 共享模式 MTS) 说明

Oracle 是一门博大精深的技术。玩了2年的oracle,依旧还有很多知识点不清楚。 昨天群里的朋友提到了 DEDICATED 和 SHARE 两种模式。 不清楚，默默的做点功课了。从网上搜了点知识，整理如下：

专用服务器（DEDICATED）：一个客户端连接对应一个服务器进程

共享服务器（SHARE）：多个客户端连接对应一个服务器进程，服务器端存在一个进程调度器来管理。它必须使用net services.也就是说必须配置tns。它适合用于高并发，事物量小，如果这个时候采用了共享模式，可以大大减少由于高度并发对于ORACLE服务器的资源消耗。

共享服务器体系：客户进程最终与一个调度程序连接，PMON进程注册了调度程序的位置和负荷，使监听器能够提交到负荷最小的调度程序。一个调度程序能并发地支持多重的客户连接。
使用SGA中的Larger pool

专用服务器体系：每个客户进程与专用服务器进程连接。服务器进程没被任何另外的客户共享。

TNS两种分别的配置模式

DEDICATE方式

OR100=

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.100)(PORT = 1521))

)

(CONNECT_DATA =

(SERVICE_NAME = orac)

)

)

share mode

TODB_MTS =

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.2)(PORT = 33166))

)

(CONNECT_DATA =

(SERVER = SHARED)

(SERVICE_NAME = dbname)

)

一、什么是MTS

MTS = Multi-Threaded ServerMTS是ORACLE SERVER的一个可选的配置选择，是相对DEDICATE方式而言，它最大的优点是在以不用增加物理资源（内存）的前提下支持更多的并发的连接。Joseph C.Johnson以餐馆给出一个MTS的形象的比喻　　

　　假设ORACLE是一家餐馆，当你走进一家餐馆时你感觉最舒服的服务方式就是有一个专门的waiter来为你服务，而不管餐馆中来了多少人，她只对你请求应答，这是DEDICTE的处理方式，也就是说每一个ORACLE客户端的连接都有一个专门的服务进程来为它服务。而大部的餐馆的服方式都不是一对一的，当你走进的时侯，你就被指定了一个waiter，她也可能为其它桌服着务，这对于餐馆来说是最有利的，因为他们可以服务更多的客人而不需要增加他们的员工。这样对你来说也可能是不错的，如果餐馆不是太忙，她服务的客人的请求都很简短且容易完成，你的感觉也好像自己拥有一个专门的waiter，waiter把你的ORDER转给厨师，然后把做好的菜拿给你，这就是MTS的处理方式，这些共享的waiters我们叫她们为Dispatchers，厨师我们则叫他们为Shared
Server Processes。在ORACLE中process的数量一定要比dispatcher多.

二、MTS架构

[metalink-Note:29038.1]1. Oracle Multi-Threaded Server Architecture.

----------------------------------------------

+-----------+ user

+-----------+| processes

| ||

|APPLICATION||

| CODE ||

| |+

+-----------+

/|\

| CLIENT

- - - - - - - - - - - - - - - - - - - - - - - - - - - - -

| SERVER

\|/

+----------------------------------+

+----------------------------------+|

| ||

| DISPATCHER PROCESSES ||

| |+

+----------------------------------+

| /|\

| |

| +-----------+ |

| +-----------+| shared |

| +-----------+|| server |

| | ORACLE ||+ processes |

| |SERVER CODE|+ |

| +-----------+ |

| /|\ /|\ | |

| | | | |

| | | | |

| | \|/ | |

+---------------|-----|-------|----------------|-------+

| \|/ | \|/ | |

| +-------------------+ +----------------------+ |

| | REQUEST | | RESPONSE QUEUES | |

| | QUEUES | +----------------------+ |

| +-------------------+ |

| SYSTEM GLOBAL AREA |

| |

+------------------------------------------------------+

Client Connections to MTS

~~~~~~~~~~~~~~~~~~~~~~~~~

A client process wanting to connect to an Oracle instance using MTS

should go through the following steps: a) Call the listener

b) The listener tells it to call back on the address where

the dispatcher is listening (a REDIRECT)

c) The client calls the dispatcher and establishes a connection.

d) The dispatcher now has a CLIENT connection ESTABLISHED and

will also continue to listen for any new connections.

e) The client sends a SQL message to the dispatcher.

f) The dispatcher unwraps this message packet and places the

request onto a queue in the SGA (System Global Area).

This queue has NOTHING to do with SQL*Net. The SQL*Net

layer ends in the dispatcher.

g) A shared server will pick up the request from the SGA queue

and process it. When there is any result this is placed

on a separate queue in the SGA ready for the dispatcher.

h) The dispatcher picks up the response message from the SGA

and wraps this into a SQL*Net message. This is passed

back to the client.

三、确定你的DB是否在使用MTS

[metalink-Note:1071305.6]Solution Description:

=====================

Look at the "init.ora" parameter MTS_DISPATCHERS.

MTS_DISPATCHERS defines the number of dispatchers created when the instance

starts up. If this is set to zero, or is null (default value), then you are NOT

using MTS.If MTS_DISPATCHERS is greater than zero, then check these other "init.ora"

parameters for valid values: MTS_MAX_DISPATCHERS Maximum number of dispatchers

MTS_SERVERS Number of server processes created at startup

MTS_MAX_SERVERS Maximum number of shared server processes

MTS_SERVICE SID

MTS_LISTENER_ADDRESS Configuration of the listener

Solution Explanation:

=====================

These other "init.ora" parameters may have valid values, but if MTS_DISPATCHERS

is zero or null, MTS is not being used.

四、MTS相关参数的含义

[metalink-Note:29038.1]The main parameters required to start MTS are:o MTS_SERVICE - This parameter establishes the name of the MTS service

that clients connect to, in order for the dispatchers to handle requests.

o MTS_DISPATCHERS - Dispatchers are detached processes that handle client

process requests and communicate them to server processes for execution. This parameter defines the number of dispatchers to startup for

each protocol that is configured for MTS. For example,

mts_dispatchers = "ipc, 2"o MTS_SERVERS - This is the number of shared server processes that

start at instance startup time. Shared servers service the

client requests passed on to them by the dispatchers.o MTS_LISTENER_ADDRESS - This is the full address for dispatchers to listen

on, and is the same as the address configured in the TNS listener. The

address specification is protocol-specific. For example: mts_listener_address = "(address=(protocol=ipc)(key=sw))"

五、使用MTS连接DB

先在主机命令行 $ lsnrctl services;"D000" established:0 refused:0 current:1 max:972 state:ready

DISPATCHER <machine: db1, pid: 3950>

(ADDRESS=(PROTOCOL=tcp)(HOST=eagle1)(PORT=33166))；查看dispather的监听端口号——33166。(dispather进程名称一般是 ora_dNNN_SID,NNN in (000-999))在client端的tnsname.ora中，注意：TODB_MTS =

(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.2)(PORT = 33166))

)

(CONNECT_DATA =

(SERVER = SHARED)

(SERVICE_NAME = dbname)

)

)这样可以解决ora-12520问题(当然这只是解决方法之一)

六、一问一答

Q：MTS一定比Delicated模式好吗？A：不是。如果硬件好点，建议使用Delicated模式。biti语录：“我是能不用MTS就不用”

Q：MTS与Delicated模式可以相互转换吗？A：可以。MTS => DelicatedReset the MTS Parameters in init.ora and reopen your DB.Delicated => MTSAdded the MTS Parameters in init.ora and reopen your DB.

Q：MTS模式下可以用Delicated连进来吗？A：可以。(SERVER = Delicated)即可。反之则不行。

Q：RAC环境一定得是MTS吗？A：不是。

Q：JDBC thin 支持MTS吗？A：目前不支持。

更多资料请见

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