oracledblink造成遠程數據庫session過多

現場報網公司數據庫連不上，先檢查了下數據庫processes=1500,session=2200.我覺得很大啊，這個數據庫沒有幾個人用。

查看v$session中的session最多是哪個machine發起的，發現是省公司的數據庫發起的session，找開發梳理了下業務，省公司同步dblink操作網公司表，且是通過weblogic的連接池。

哦，有點明白了，是dblink引起的，weblogic連接池是一直存在的，所以在網公司端session是不釋放的，如果省公司把應用都停掉，那在網公司端的session都會釋放。要驗證想法，做個試驗：

目標：數據庫A上建dblink,修改數據庫B上的表。

環境准備：

1.在數據庫A上建dblink

create public database link TO_B
connect to TEST_DB identified by TEST_DB
using '(DESCRIPTION =(ADDRESS_LIST =(ADDRESS = (PROTOCOL = TCP)(HOST = 10.10.15.150)(PORT = 1521)))(CONNECT_DATA =(SID = orcl)))';

2.在數據庫B上建表

create table TEST( ID NUMBER );

insert into test values(1);

開始測試：

1.在數據庫B上select count(1) from v$session;

2.在數據庫A上update test@TO_B set id=1;

commit;

3.在數據庫B上select count(1) from v$session; 可以看到漲了一個

對比測試：

1.在數據庫B上select count(1) from v$session;

2.在數據庫A上update test@TO_B set id=1;

commit;

alter session close database link TO_B;

3.在數據庫B上select count(1) from v$session; 可以看到沒有變化

附錄為官方文檔：

32 Managing a Distributed Database

Closing Database Links

If you access a database link in a session, then the link remains open until you close the session. A link is open in the sense that a process is active on each of the remote databases accessed through the link. This situation has the following consequences:

If 20 users open sessions and access the same public link in a local database, then 20 database link connections are open.

If 20 users open sessions and each user accesses a private link, then 20 database link connections are open.

If one user starts a session and accesses 20 different links, then 20 database link connections are open.

After you close a session, the links that were active in the session are automatically closed. You may have occasion to close the link manually. For example, close links when:

The network connection established by a link is used infrequently in an application.

The user session must be terminated.

To close a link, issue the following statement, where linkname refers to the name of the link:

ALTER SESSION CLOSE DATABASE LINK linkname;

Note that this statement only closes the links that are active in your current session.