ORA-02020 too many database links in use重現

在A庫上建DB_link，更新B庫。報ORA-2020 too many database links in use，是要設置OPEN_LINKS和OPEN_LINKS_PER_INSTANCE兩個參數，它們的默認值都是4。

alter system set open_links=200 scope=both;

alter system set open_links_per_instance=200 scope=both;

問題來了，是修改A庫中的參數還是B庫，是修改A庫的。

修改這類參數數據庫要重啟。

ORA-02020: too many database links in use

Cause: The current session has exceeded the INIT.ORA open_links maximum.

Action: Increase the open_links limit, or free up some open links by committing or rolling back the transaction and canceling open cursors that reference remote databases.

OPEN_LINKS specifies the maximum number of concurrent open connections to remote databases in one session.

OPEN_LINKS_PER_INSTANCE specifies the maximum number of migratable open connections globally for each database instance.

OPEN_LINKS_PER_INSTANCE is different from OPEN_LINKS, which indicates the number of connections from a session. The OPEN_LINKS parameter is not applicable to XA applications.

OPEN_LINKS_PER_INSTANCE跟OPEN_LINKS的區別是，前者是對于XA事務的。

做個試驗重現一下：

在A庫上：

SQL> show parameter open_link

NAME ? ? ? ? ? ? ? ? ? ? ? ? ?TYPE ? ? ? ?VALUE

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

open_links ? ? ? ? ? ? ? ? ? ?integer ? ? ?4

open_links_per_instance ? ? ? integer ? ? ?4

create database link DBLINK_1

connect to TEST IDENTIFIED BY test

using '(DESCRIPTION =

(ADDRESS_LIST =

(ADDRESS = (PROTOCOL = TCP)(HOST = 10.10.15.150)(PORT = 1521))

)

(CONNECT_DATA =

(SERVICE_NAME = orcl)

)

)';

--按照同種方式建5個dblink

SQL> set serveroutput on

SQL> ?declare

2 ? ? ? v_i number;

3 ? ? ? v_sql varchar(500);

4 ? ?begin

5 ? ? ?for i in 1..5

6 ? ? ? loop

7 ? ? ? ?v_sql:='select count(*) from dual@DBLINK_'||i;

8 ? ? ? ?execute immediate v_sql into v_i;

9 ? ? ? ?dbms_output.put_line('DBLINK_'||i);

10 ? ? ? ?commit;

11 ? ? ? end loop;

12 ? ?end;

13 ?/

DBLINK_1

DBLINK_2

DBLINK_3

DBLINK_4

DBLINK_5

PL/SQL procedure successfully completed

SQL>

SQL> ?declare

2 ? ? ? v_i number;

3 ? ? ? v_sql varchar(500);

4 ? ?begin

5 ? ? ?for i in 1..5

6 ? ? ? loop

7 ? ? ? ?v_sql:='select count(*) from dual@DBLINK_'||i;

8 ? ? ? ?execute immediate v_sql into v_i;

9 ? ? ? ?dbms_output.put_line('DBLINK_'||i);

10 ? ? ? ?--commit;

11 ? ? ? end loop;

12 ? ?end;

13 ?/

DBLINK_1

DBLINK_2

DBLINK_3

DBLINK_4

declare

v_i number;

v_sql varchar(500);

begin

for i in 1..5

loop

v_sql:='select count(*) from dual@DBLINK_'||i;

execute immediate v_sql into v_i;

dbms_output.put_line('DBLINK_'||i);

--commit;

end loop;

end;

ORA-02020: 過多的數據庫鏈接在使用中

ORA-06512: 在 line 9

SQL> ? declare

2 ? ? ? v_i number;

3 ? ? ? v_sql varchar(500);

4 ? ?begin

5 ? ? ?for i in 1..4

6 ? ? ? loop

7 ? ? ? ?v_sql:='select count(*) from dual@DBLINK_'||i;

8 ? ? ? ?execute immediate v_sql into v_i;

9 ? ? ? ?dbms_output.put_line('DBLINK_'||i);

10 ? ? ? ?--commit;

11 ? ? ? end loop;

12 ? ?end;

13 ?/

DBLINK_1

DBLINK_2

DBLINK_3

DBLINK_4

PL/SQL procedure successfully completed

SQL> commit;

Commit complete

--分兩次執行

SQL> declare

2 ? ? ? v_i number;

3 ? ? ? v_sql varchar(500);

4 ? ?begin

5 ? ? for i in 1..3

6 ? ? ? loop

7 ? ? ? ?v_sql:='select count(*) from dual@DBLINK_'||i;

8 ? ? ? ?execute immediate v_sql into v_i;

9 ? ? ? ?dbms_output.put_line('DBLINK_'||i);

10 ? ? ? ?--commit;

11 ? ? ? end loop;

12 ? ?end;

13 ?/

DBLINK_1

DBLINK_2

DBLINK_3

PL/SQL procedure successfully completed

SQL> ? declare

2 ? ? ? v_i number;

3 ? ? ? v_sql varchar(500);

4 ? ?begin

5 ? ? for i in 4..5

6 ? ? ? loop

7 ? ? ? ?v_sql:='select count(*) from dual@DBLINK_'||i;

8 ? ? ? ?execute immediate v_sql into v_i;

9 ? ? ? ?dbms_output.put_line('DBLINK_'||i);

10 ? ? ? ?--commit;

11 ? ? ? end loop;

12 ? ?end;

13 ?/

DBLINK_4

declare

v_i number;

v_sql varchar(500);

begin

for i in 4..5

loop

v_sql:='select count(*) from dual@DBLINK_'||i;

execute immediate v_sql into v_i;

dbms_output.put_line('DBLINK_'||i);

--commit;

end loop;

end;

ORA-02020: 過多的數據庫鏈接在使用中

ORA-06512: 在 line 9

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