Question

In a DB2 federated database (based on remote servers and nicknames), I need to clean up the model and recreate it from another database. I need to delete every database object except those servers and nicknames.

I know how to retrieve the list of objects from the SYSCAT schema. Now I need to run the DROP statements on each. Obviously the dependencies will get in the way.

The brute force approach would be to run the DROPs in a loop until all have succeeded, but depending on the order (lucky or not), it could take a very long time.

Would you know a way to efficiently order the DROP statement so that the total time for the deletion is the shortest possible?

A perfect solution is not expected. A reasonably clever solution is good enough.

Thank you

Answer 1

This query is able to order the statements according to the total number of elements they depend on. The resulting order works almost without a glitch, the second pass of the “brute force” approach contains only a handful of objects (out of several thousands objects to delete).

Problem, it is very slow…

EDIT : There was a typo in the query that made it return more or less correct data but very very slowly.

WITH FIRST_LEVEL_DEPENDENCIES (BSCHEMA, BNAME, DTYPE, DSCHEMA, DNAME) AS
(
  SELECT T1.TABSCHEMA AS BSCHEMA, T1.TABNAME AS BNAME, T1.BTYPE, T1.BSCHEMA, T1.BNAME
    FROM SYSCAT.TABDEP T1
   WHERE T1.TABSCHEMA NOT LIKE 'SYS%'
     AND T1.BTYPE <> 'N'
   UNION ALL
  SELECT T1.ROUTINESCHEMA AS BSCHEMA, T1.SPECIFICNAME AS BNAME, T1.BTYPE, T1.BSCHEMA, T1.BNAME
    FROM SYSCAT.ROUTINEDEP T1
   WHERE T1.ROUTINESCHEMA NOT LIKE 'SYS%'
     AND T1.BTYPE <> 'N'
   UNION ALL
  SELECT T1.TABSCHEMA AS BSCHEMA, T1.TABNAME AS BNAME, 'T', T1.REFTABSCHEMA, T1.REFTABNAME
    FROM SYSCAT.REFERENCES T1
   WHERE T1.TABSCHEMA NOT LIKE 'SYS%'
),
RECURSIVE_DEPENDENCIES (LEVEL, BSCHEMA, BNAME, DTYPE, DSCHEMA, DNAME) AS
(
   SELECT 1, U.BSCHEMA, U.BNAME, U.DTYPE, U.DSCHEMA, U.DNAME
     FROM FIRST_LEVEL_DEPENDENCIES AS U
    UNION ALL
   SELECT LEVEL + 1, REC.BSCHEMA, REC.BNAME, U.DTYPE, U.DSCHEMA, U.DNAME
     FROM RECURSIVE_DEPENDENCIES REC,
          FIRST_LEVEL_DEPENDENCIES U
    WHERE LEVEL < 6
      AND U.BSCHEMA = REC.DSCHEMA
      AND U.BNAME = REC.DNAME
)
SELECT BSCHEMA, BNAME, COUNT(*)
  FROM RECURSIVE_DEPENDENCIES
 GROUP BY BSCHEMA, BNAME
 ORDER BY COUNT(*)