前几天在客户现场，检查一个数据库时发现在OS上根本没有明确的数据库连接，但是在数据库内部却可以看到会话信息。

    想了一会，才明白过来，原来这是一个MTS系统，共享服务器模式已经很久没有遇到了，几乎忘却了。

    在检查会话信息时，你会发现，用户进程的进程地址PADDR是相同的，都是812960DC ：

    SQL> select paddr,sid,username,osuser,process,terminal,machine,logon_time from v$session;

    PADDR           SID USERNAME   OSUSER     PROCESS      TERMINAL        MACHINE                        LOGON_TIME

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

    8129301C          1            oracle     6568         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:07

    812933DC          2            oracle     6570         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:08

    8129379C          3            oracle     6573         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:08

    81293B5C          4            oracle     6576         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    81293F1C          5            oracle     6578         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    812942DC          7            oracle     6580         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    8129469C          9            oracle     6582         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    81294A5C         10            oracle     6584         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    81294E1C         11            oracle     6586         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    812951DC         12            oracle     6588         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    8129559C         13            oracle     6590         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    PADDR           SID USERNAME   OSUSER     PROCESS      TERMINAL        MACHINE                        LOGON_TIME

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

    8129595C         14            oracle     6592         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:11

    812960DC         15 EYGLE      eyg        3572:220     EYGLEE          EYGLEENMO\\EYGLEE               2010-10-28 09:04:14

    812960DC         16 EYGLE      eyg        1804:3708    EYGLEE          EYGLEENMO\\EYGLEE               2010-10-28 09:04:19

    8129685C         17            oracle     6611         UNKNOWN         EYGLEORACLE1                   2010-09-27 11:39:13

    81295D1C         20 EYGLE      root                    unknown         EYGLEWEB1                      2010-10-28 07:45:30

    812960DC         24 EYGLE      root                    unknown         EYGLEWEB1                      2010-10-28 09:11:13

    812960DC         30 EYGLE      eyg        3296:2968    EYGLEE          EYGLEENMO\\EYGLEE               2010-10-28 09:04:22

    812960DC         31 EYGLE      root                    unknown         EYGLEWEB1                      2010-10-28 08:21:09

    812960DC         32 EYGLE      root                    unknown         EYGLEWEB1                      2010-10-28 09:13:45

    812960DC         33 EYGLE      oracle     721122                       oracle2                        2010-10-13 13:34:13

    8129649C         35 SYS        oracle     23221        pts/1           EYGLEORACLE1                   2010-10-28 09:24:21

    而 812960DC  进程正是Dispatcher进程 oracle@EYGLEORACLE1 (D000)

    SQL> select addr,spid,program from v$process;

    ADDR     SPID         PROGRAM

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

    81292C5C              PSEUDO

    8129301C 6568         oracle@EYGLEORACLE1 (PMON)

    812933DC 6570         oracle@EYGLEORACLE1 (DIAG)

    8129379C 6573         oracle@EYGLEORACLE1 (LMON)

    81293B5C 6576         oracle@EYGLEORACLE1 (LMD0)

    81293F1C 6578         oracle@EYGLEORACLE1 (LMS0)

    812942DC 6580         oracle@EYGLEORACLE1 (LMS1)

    8129469C 6582         oracle@EYGLEORACLE1 (DBW0)

    81294A5C 6584         oracle@EYGLEORACLE1 (LGWR)

    81294E1C 6586         oracle@EYGLEORACLE1 (CKPT)

    812951DC 6588         oracle@EYGLEORACLE1 (SMON)

    ADDR     SPID         PROGRAM

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

    8129559C 6590         oracle@EYGLEORACLE1 (RECO)

    8129595C 6592         oracle@EYGLEORACLE1 (CJQ0)

    81295D1C 6594         oracle@EYGLEORACLE1 (S000)

    812960DC 6596         oracle@EYGLEORACLE1 (D000)

    8129649C 23222        oracle@EYGLEORACLE1 (TNS V1-V3)

    8129685C 6611         oracle@EYGLEORACLE1 (LCK0)

    81296FDC 9955         oracle@EYGLEORACLE1 (S003)

    而通过监听器也可以看到，数据库所有的连接都来自Dispatcher，没有Dedicated模式的连接建立：

    [oracle@EYGLEORACLE1 log]$ lsnrctl service

    LSNRCTL for Linux: Version 9.2.0.7.0 - Production on 28-OCT-2010 09:38:51

    Copyright (c) 1991, 2002, Oracle Corporation.  All rights reserved.

    Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=jgzx1)(PORT=1521)))

    Services Summary...

    Service "PLSExtProc" has 1 instance(s).

     Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...

     Handler(s):

     "DEDICATED" established:0 refused:0

     LOCAL SERVER

    Service "jgzx" has 2 instance(s).

     Instance "jgzx1", status READY, has 3 handler(s) for this service...

     Handler(s):

     "DEDICATED" established:0 refused:0 state:ready

     REMOTE SERVER

     (ADDRESS=(PROTOCOL=TCP)(HOST=jgzx1)(PORT=1521))

     "DEDICATED" established:0 refused:0 state:ready

     LOCAL SERVER

     "D000" established:117664 refused:0 current:21 max:1002 state:ready

     DISPATCHER

     (ADDRESS=(PROTOCOL=tcp)(HOST=jgzx1)(PORT=32812))

     Instance "jgzx2", status READY, has 2 handler(s) for this service...

     Handler(s):

     "DEDICATED" established:0 refused:0 state:ready

     REMOTE SERVER

     (ADDRESS=(PROTOCOL=TCP)(HOST=jgzx2)(PORT=1521))

     "D000" established:114273 refused:0 current:18 max:1002 state:ready

     DISPATCHER

     (ADDRESS=(PROTOCOL=tcp)(HOST=jgzx2)(PORT=32784))

    Service "jgzx1" has 1 instance(s).

     Instance "jgzx1", status UNKNOWN, has 1 handler(s) for this service...

     Handler(s):

     "DEDICATED" established:0 refused:0

     LOCAL SERVER

    The command completed successfully

    由此，MTS模式的特点显而易见，其减少进程可以缩减系统的资源消耗，但是显然会导致排队，并不适用于对响应时间要求较高的OLTP系统。

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