How to select between sequences on different DB links when one DB is down

Question

Hi!
I'm running Oracle 11.1.0.7.0 on HPUX v3 in a Stream replicated environment.
One of the applications would need to connect to both DBs ensuring some consistency across sequences defined locally.
We cannot use odd/even approach in the sequences so that I thought we may take the greatest value of the two sequences (one on each node).
The SQL would look like:
select greatest(user.SEQ_NUMBER.nextval@DB_B,user.SEQ_NUMBER.nextval@DB_A) from dual;
it works fine but only in a sunny day scenario, i.e. when both nodes are up and running. In case of issues with one of the DBs I would get:
ERROR at line 1:
ORA-12541: TNS:no listener
Is there any way to intercept this error and take the value from the local DB ?
Thanks,
Mike

Answer 1

Hi Mike,
Maybe something like this would help you:
  1  create or replace function f1 return number as
  2  lv_stmt varchar2(128);
  3  lv_ret  number;
  4  begin
  5   lv_stmt := 'select 1 from dual@dummy_dblnk';
  6   execute immediate lv_stmt into lv_ret;
  7  exception
  8   when others then
  9    if sqlcode = -2019 then
10      return -1;
11    else
12     raise;
13    end if;
14* end;
SQL> /
Function created.
SQL> save f1 replace
Wrote file f1.sql
SQL> SELECT f1 FROM dual;
        F1
        -1Thanks,
Lukasz