Why??? Simple snapshot can not refresh automatically, but can refresh manually.

Question

Server 1 : Oracle 7.3.4 (as a Master site)
Server 2 : Oracle 7.3.4 (as a Snopshot site)
Client PC: SQL*Plus (Oracle 7.3.4 Client)
Step 1: on Client PC, start 2 SQL*Plus dialog Windows,
one(Window A) for <Server 1> , another(Window B) for <Server 2>;
Step 2: on <Window A> do:
SQL>connect scott/tiger@Server1
SQL>CREATE SNAPSHOT LOG ON scott.dept ;
SQL>select * from dept;
DEPTNO DNAME LOC
10 AAAAAA AAAAA
20 BBBBBB AAAAA
30 CCCCCC AAAAA
Step 3: on <Window B> do:
SQL>connect scott/tiger@Server2
SQL>CREATE DATABASE LINK oracle USING 'Server1';
SQL>CREATE SNAPSHOT all_dept REFRESH fast
start with sysdate NEXT SYSDATE+1/(24*60)
AS SELECT * FROM scott.dept@oracle;
-- refresh interval: 1 minute
SQL>select * from all_dept;
DEPTNO DNAME LOC
10 AAAAAA AAAAA
20 BBBBBB AAAAA
30 CCCCCC AAAAA
Step 4: on <Window A> do:
SQL>insert into dept values (50,'MMMMMM','NNNNN');
SQL>commit;
SQL>select * from dept;
DEPTNO DNAME LOC
10 AAAAAA AAAAA
20 BBBBBB AAAAA
30 CCCCCC AAAAA
50 MMMMMM NNNNN
<one or two minutes later ... ... >
Step 5: on <Window B> do:
SQL>select * from all_dept;
DEPTNO DNAME LOC
10 AAAAAA AAAAA
20 BBBBBB AAAAA
30 CCCCCC AAAAA
conclusion: Simple snapshot can not refresh automatically ???????
SQL>exec DBMS_SNAPSHOT.REFRESH( list => 'all_dept',method => 'F');
SQL>select * from all_dept;
DEPTNO DNAME LOC
10 AAAAAA AAAAA
20 BBBBBB AAAAA
30 CCCCCC AAAAA
50 MMMMMM NNNNN
conclusion:Simple snapshot can refresh manually.
How to solve this problem?????
Thank you very much
Zhang Ming-an

Answer 1

When you are manually refreshing the snapshot as scott/tiger, and your database link was defined with a 'connect to/identified by ' clause, your login credentials will be scott/tiger. When the refresh happens from the job queue, it does not use those credentials, It uses some default set. What you should probably do is:
1. create public database link Oracle using 'server1';
2. as scott/tiger, create database link Oracle connect to scott identified by tiger;
3. your automatic refresh should work now.