Acquire with NOWAIT error and TRUNCATE command

Question

Why is it that, sometimes when i try to TRUNCATE a table. I would get
ORA-00054: resource busy and acquire with NOWAIT specified error. And i would be able to DELETE the same table using DELETE FROM table_name;
Message was edited by:
C. Boutet

Answer 1

Because some other session has a lock on that table, you can delete it because you are in fact deleting your read consistent view of the table. See this test case:
In session 1:
YAS@10G>create table t as select * from dual;
Table created.
YAS@10G>insert into t values(2);
1 row created.In session 2:
YAS@10G>truncate table t;
truncate table t
ERROR at line 1:
ORA-00054: resource busy and acquire with NOWAIT specified
YAS@10G>delete from t;
1 row deleted.
YAS@10G>commit;
Commit complete.
YAS@10G>select * from t;
no rows selectedI was not able to truncate it because session 1 inserted a row and it is holding a lock on the table. I could delete from the table because the rows I want to delete are not locked.
TRUNCATE is DDL and it needs an exclusive lock on the table. Session 1 is holding a shared lock on the table which does not permit the other session to get an exclusive lock.