[20190306]共享服务模式与SDU.txt

--//一些文档提到共享服务模式,服务端SDU=65535,测试验证看看.
--//链接:https://blogs.sap.com/2013/02/07/oracle-sqlnet-researching-setting-session-data-unit-sdu-size-and-how-it-can-go-wrong/
Official Oracle 11g R2 documentation

Under typical database configuration, Oracle Net encapsulates data into buffers the size of the session data unit (SDU)
before sending the data across the network. Oracle Net sends each buffer when it is filled, flushed, or when an
application tries to read data. Adjusting the size of the SDU buffers relative to the amount of data provided to Oracle
Net to send at any one time can improve performance, network utilization, and memory consumption. When large amounts of
data are being transmitted, increasing the SDU size can improve performance and network throughput.

The amount of data provided to Oracle Net to send at any one time is referred to as the message size. Oracle Net assumes
by default that the message size will normally vary between 0 and 8192 bytes, and infrequently, be larger than 8192
bytes. If this assumption is true, then most of the time, the data is sent using one SDU buffer.

The SDU size can range from 512 bytes to 65535 bytes. The default SDU for the client and a dedicated server is 8192
bytes. The default SDU for a shared server is 65535 bytes.

The actual SDU size used is negotiated between the client and the server at connect time and is the smaller of the
client and server values. Configuring an SDU size different from the default requires configuring the SDU on both the
client and server computers, unless you are using shared servers. For shared servers, only the client value must be
changed because the shared server defaults to the maximum value.
--//注意理解最后一段: For shared servers, only the client value must be changed because the shared server defaults to
--//the maximum value.也就是在共享服务器模式下服务端SDU设置65535,以client端要设置为准,我开始理解错误.
--//实际上服务端应该也是可以改变的,修改dispatchers参数.

1.环境:
SCOTT@book> @ ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

--//在client建立sql脚本e2.txt:
R:\>cat e1.txt
select sysdate,P2,TIME_SINCE_LAST_WAIT_MICRO from V$SESSION_WAIT_HISTORY where sid=&&1 and event='SQL*Net more data from client';

R:\> cat e2.txt
select /*
0014567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
0024567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
...snip...
5994567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
6004567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
*/ sysdate
from dual;

R:\>ls -l  e2.txt
-rw-rw-rw-   1 user     group       61235 Mar  6 16:46 e2.txt

--//说明服务端监听配置以及sqlnet.ora采用缺省配置SDU.
--//修改client端sqlnet.ora加入DEFAULT_SDU_SIZ