I am only an egg, so I hope someone else can explain this to me.
Oracle Enterprise Edition 8.1.7.4.1 on Windows 2000
I was experimenting to see if an "alter table enable validate constraint" would cause
DML statements to wait. I thought it wouldn't. But in real life I see something
different.
I have a table X (object_id 429995) with about 100 million rows. In one session (sid
15) I enable a check constraint, and in another session (sid 14) I simultaneously
delete a few rows from the table. The delete "waits" on the enable constraint to
complete, and it's waiting on a library cache lock. Why would that be? At the end of
this e-mail you can see the contents of DBA_LOCKS, V$LOCKED_OBJECT, V$SESSION_WAIT. I
read the system state dump and I still don't understand why there would be a library
cache lock.
Session ID 15
--- sid-15-SQL1
alter table hes_a_keeper.many_rows add
(constraint ck1 check (dummy_column > 'B') disable) ;
--- sid-15-SQL2 (simultaneous with sid-14-SQL1)
alter table hes_a_keeper.many_rows enable validate constraint ck1 ;
Session ID 14
--- sid-14-SQL1 (simultaneous with sid-15-SQL2)
delete from hes_a_keeper.many_rows where rownum < 10 ;
Session ID 10
--- statements issued while sid-14-SQL1 and sid-15-SQL2 are running
alter session set events 'immediate trace name systemstate level 10' ;
select * from dba_locks where session_id in (14,15) ;
select * from v$locked_object where object_id = 429995 ;
select * from v$session_wait where sid in (14,15) ;
SQL> select * from dba_locks where session_id in (14,15) ;
SESSION_ID LOCK_TYPE MODE_HELD
---------- -------------------------- ----------------------------------------
MODE_REQUESTED LOCK_ID1
---------------------------------------- ----------------------------------------
LOCK_ID2 LAST_CONVERT BLOCKING_OTHERS
---------------------------------------- ------------
----------------------------------------
15 DML Share
None 429995
0 10 Not Blocking
SQL> select * from v$locked_object where object_id = 429995 ;
XIDUSN XIDSLOT XIDSQN OBJECT_ID SESSION_ID ORACLE_USERNAME
--------- --------- --------- --------- ---------- ------------------------------
OS_USER_NAME PROCESS LOCKED_MODE
------------------------------ --------- -----------
0 0 0 429995 15 JRK
jkilchoe 1540:260 4
SQL> select * from v$session_wait where sid in (14,15) ;
SID SEQ# EVENT
--------- --------- ----------------------------------------------------------------
P1TEXT P1 P1RAW
---------------------------------------------------------------- --------- --------
P2TEXT P2 P2RAW
---------------------------------------------------------------- --------- --------
P3TEXT P3 P3RAW
WAIT_TIME
---------------------------------------------------------------- --------- --------
---------
SECONDS_IN_WAIT STATE
--------------- -------------------
15 5005 db file scattered read
file# 13 0000000D
block# 19516 00004C3C
blocks 8 00000008
0
0 WAITING
14 142 library cache lock
handle address 47483828 02D48BB4
lock address 40114204 0264181C
10*mode+namespace 21 00000015
0
9 WAITING
SQL>
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--
Author: Jacques Kilchoer
INET: [EMAIL PROTECTED]
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