After setting up dg4odbc to connect to a SQL Server database (read ‘Tips on Using dg4odbc on 64-bit Linux’), I spent last week trying to get refreshes of materialized views to work in 11g, using the same DDL as in 8i. I was very frustrated to see the refreshes break in 11g.

The DDL gives no obvious clues. The remote table:

desc MYTABLE@SQLSERVER
Name                           Null?    Type
------------------------------ -------- ----------------------------
MY_ID                          NOT NULL NUMBER(5)
MY_DESC                        NOT NULL VARCHAR2(40)

SQL> create materialized view MV_MYTABLE
2 as select *
3 FROM   MYTABLE@SQLSERVER
4 WHERE  MY_ID IS NOT NULL
5 AND    MY_DESC IS NOT NULL;

Materialized view created.

SQL> begin
2  DBMS_SNAPSHOT.REFRESH( 'MV_MYTABLE','C');
3  end;
4  /
begin
*
ERROR at line 1:
ORA-12008: error in materialized view refresh path
ORA-01400: cannot insert NULL into (%s)
ORA-02063: preceding line from SQLSERVER
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2537
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2743
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 2712
ORA-06512: at line 2

The reason, it turns out, is the ANSI-compliance of dg4odbc. The remote table has a row where the column MY_DESC is storing a '' (a zero-length string).

SQL Server treats the zero-length string as different from NULL. Oracle 11g treats zero-length strings as the same as NULL. (more…)

From time to time, we get DBMS_JOB failures for failed refreshes that happen due to broken database links.

The error in the alert.log is ORA-12012: error on auto execute of job {number}, followed by one of ORA-12547: TNS:lost contact, ORA-12170: TNS:Connect timeout occurred, ORA-12541: TNS:no listener, or any other of the network connection failures.

I usually have a quick look into DBA_JOBS to find out the materialized view (MV) name and then peak into the DBA_MVIEWS.MASTER_LINK column.

However, I have a client with refreshes scheduled using MV refresh groups, and it took me a while to recall the view name, asking around and RTFM’ing. Since this situation comes up regularly, I wrapped up a quick script that parses job content, takes in account MV refresh groups, and outputs the database link(s) involved. I think it could be useful to few others so here it goes: (more…)