Weird DB Link Behaviour

Question

I have encountered a problem whereby Oracle considers that a user's session is distributed. This means that when a rollback occurs, they get an ORA-02055 error. Initially, my form was doing a select on a view which referenced a DB Link. This code was causing the problem, so I changed it to a call to a server-side procedure using an autonomous transaction to attempt to insulate the form from the DB Link. This partially solved the problem, but not entirely.
Now, when I exit the form, even if I have done a commit within it, the transaction is considered by Oracle to be distributed. (I am checking this by querying SYS.V$RESOURCE_LIMIT). The only workaround seems to be to do another commit in the calling form on returning.
Anyone got any idea what is going on here?
Chris

Answer 1

From my experience using DB links within a forms application, you need to be aware of 2 things:
1)You should only be referencing the linked data from the database. In other words place your links in DB packages or procudures in the DB that your form can access. You should not be calling your links directly from the form. The main reason is that forms pl/sql and the DB pl/sql engines are different.
2) Anytime a link is accessed it opens a db link to the linked DB and creates a session on the linked DB. This link must be explicetly closed. To do this the session on the linked DB must be either commited or rolled back. Then close your link. See below server side package code example. It would be this code that your form would call. If your form needs to interact with the dataset returned by the link then you will need to write additional code to return the dataset from the DB package to your form (function).
DECLARE
lt_return_table Package.table_spec@DB_link;
BEGIN
BEGIN
--| |
--| | RETRIEVE Linked DATA
--| |
package.some_query@DB_link(lt_return_table, var1, var2, var3);
--commit and close the link.
COMMIT;
Package.CLOSE_DB_LINK;
EXCEPTION
WHEN OTHERS THEN
--rollback and close the link.
ROLLBACK;
Package.CLOSE_DB_LINK;
END;
END;
Hope this helps
Pete