How do I view data being locked by select for update

Question

We've implemented a test appointment booking system. The application does explicit row locking (e.g. select * from calendar where ..... for update nowait;)
I need to view which database SID and USER has which records locked.
I cannot find such SQL on google or AskTom.
Currently, I can figureout which records are locked with the following PL/SQL.
set serveroutput on
declare id varchar2(20);
begin
for r in (select rowid,a.* from CALENDAR a) loop
begin
select rowid into id from CALENDAR where rowid=r.rowid for update nowait;
exception
when others then
dbms_output.put_line(r.rowid);
end;
rollback;
end loop;
rollback;
end;
Two questons:
1. How do I find out which database user and SID is locking each record.
2. Is there a more elegant way of instead of boing the above PL/SQL.
Please help?

Answer 1

Oracle is not maintaining a list of all row locks. I've been told that other RDBMS's do have such a lock manager. Oracle doesn't because it hinders scalability. The fact that a row is locked is written in the block header itself. And you can only see that a row is locked by trying to lock it yourself. If it gives an ORA-00054, the row is locked.
However, I've seldom come across a situation where I need to know which rows are locked. So what's the real reason behind your requirement "I need to view which database SID and USER has which records locked.". Why is this information important to you?
Regards,
Rob.
PS: About your code: you don't want to catch the OTHERS exception, just the ORA-00054.