oracle dblink造成远程数据库session过多

it2025-07-14 9

现场报网公司数据库连不上，先检查了下数据库processes=1500,session=2200.我认为非常大啊。这个数据库没有几个人用。

查看v$session中的session最多是哪个machine发起的。发现是省公司的数据库发起的session，找开发梳理了下业务，省公司同步dblink操作网公司表，且是通过weblogic的连接池。

哦，有点明确了，是dblink引起的。weblogic连接池是一直存在的，所以在网公司端session是不释放的。假设省公司把应用都停掉，那在网公司端的session都会释放。要验证想法。做个试验：

目标：数据库A上建dblink,改动数据库B上的表。

环境准备：

1.在数据库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.在数据库B上建表

create table TEST( ID NUMBER );

insert into test values(1);

開始測试：

1.在数据库B上select count(1) from v$session;

2.在数据库A上update test@TO_B set id=1;

commit;

3.在数据库B上select count(1) from v$session;能够看到涨了一个

对照測试：

1.在数据库B上select count(1) from v$session;

2.在数据库A上update test@TO_B set id=1;

commit;

alter session close database linkTO_B;

3.在数据库B上select count(1) from v$session;能够看到没有变化

总结：出现这样的问题。归根结底是操作dblink不规范，用了之后没有关闭。

有可能是bug:

提供反馈... 您已依据 ID 匹配定向到此 BUG。或者, 单击此处搜索此短语。隐藏 Bug 18394488 : TOO MANY CONNECTIONS OVER SHARED DBLINK AFTER UPGRADE TO 11.2.0.4 转究竟部

Bug 属性

类型B - Defect已在产品版本号中修复严重性2 - Severe Loss of Service产品版本号11.2.0.4状态36 - Duplicate Bug. To Filer平台212 - IBM AIX on POWER Systems (64-bit)创建时间2014-3-13平台版本号7.1更新时间2015-6-5基本 Bug18759589数据库版本号11.2.0.4影响平台Generic产品源Oracle与此 Bug 相关的知识, 补丁程序和 Bug

相关产品

产品线Oracle Database Products系列Oracle Database Suite区域Oracle Database产品5 - Oracle Database - Enterprise Edition Hdr: 18394488 11.2.0.4 RDBMS 11.2.0.4 PRG INTERFACE PRODID-5 PORTID-212 18759589 Abstract: TOO MANY CONNECTIONS OVER SHARED DBLINK AFTER UPGRADE TO 11.2.0.4 *** 03/13/14 12:14 am *** PROBLEM: -------- The production database system upgraded from 11.2.0.1 to 11.2.0.4 in the previous weekend. There are several shared db links on this database to other production database that its version is 11.2.0.3 . When trying to connect sessions on 11.2.0.4 to 11.2.0.3 via shared db links it opens too many connection on connected database. We tested this situation between 11.2.0.3 to 11.2.0.3 databases via shared db link , opened session count is two (one of them is PSEUDO other is DEDICATED ) but between 11.2.0.4 to 11.2.04 opened session count is at least 10. When 1000 session trying to connect 11.2.0.4 to 11.2.0.3 via shared db links about 10000 connection opening. This system working correctly before database upgrade. We didn't change any parameter, listener configuration or unix parameter. DIAGNOSTIC ANALYSIS: -------------------- Checked with the customer on: 1. Why are you using shared DBLINKS and SHARED servers ? Because main application works with shared dblinks. (from many years ) ... We didn't use shared servers , after upgrade too many connection is opening and we have to use it because of handle too many connection with less resource . 2. Can you use standard DBLINKS and not use shared servers ? We cannot use standard db links because of application design... If Oracle solve this problem we can use dedicated. (before upgrade we had used dedicated ) When checking with application development team on why are they using shared db links ; they said that main banking application works in webspehere connection pool using XA transaction and it must use shared db link to handle connections ! It can't use standart db links . If oracle created shared db link feature why are you offer to use standard db link ? Before upgrade everything works fine. I am also repeating my words , we had used dedicated server , we have to use shared server because of performance issue for now . If Oracle solve opening many connection issue we will use dedicated server again . But shared db link feautere will remain because of websphere XA transaction handling. 3. How many sessions to server B does each of your application connections to Server A open ?

Its count didn't change , anyway after upgrade it is same that the previous value before upgrade. ct found metalink document why they use shared db link. ORA-24777 reported when using a database link from within an XA coordinated transaction (Doc ID 1506756.1) Solution from document; Two options 1. Configure the database to allow the use of shared servers and then let the application use these as per the following documentation http://docs.oracle.com/cd/E11882_01/server.112/e25494/manproc003.htm#ADMIN0050 2 or establish whether the Java application needs to start an XA transaction. OR 2. Define the database link being utilised as a shared database link, i.e, CREATE SHARED DATABASE LINK .. They got this error many years ago ; ORA-24777 reported by a JDBC/XA application when utilising a database link between two Oracle databases. And db links was configured to shared db links. I explained before why we are using shared server ( performance ) A complete test case epxlaining how a connection from 11.2.0.4. to 11.2.0.3 opens alot of connections: db_link.pdf WORKAROUND: ----------- none RELATED BUGS: ------------- Bug 18157790 - ORA-22 AFTER UPGRADE FROM 11.2.0.3 TO 11.2.0.4 Bug 1559258 - PSEUDO SESSION INCREASE WITH XA + SHARED DBLINK REPRODUCIBILITY: ---------------- issue is reproducible on ct's env. TEST CASE: ---------- provided STACK TRACE: ------------ SUPPORTING INFORMATION: ----------------------- 24 HOUR CONTACT INFORMATION FOR P1 BUGS: ---------------------------------------- DIAL-IN INFORMATION: -------------------- IMPACT DATE: ------------

附录为官方文档：

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.

转载于:https://www.cnblogs.com/bhlsheji/p/5056641.html

相关资源：数据结构—成绩单生成器

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