[20190522]DISABLE TABLE LOCK.txt

[20190522]DISABLE TABLE LOCK.txt

--//如果禁止table lock时,一些ddl操作会被禁止.但是我有点吃惊的是增加字段不受限制.
--//通过测试说明问题.

1.环境:
SCOTT@book> @ ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

SCOTT@book> create table t as select rownum id from dual ;
Table created.

SCOTT@book> alter table t disable table lock;
Table altered.

2.测试:
SCOTT@book> truncate table t;
truncate table t
               *
ERROR at line 1:
ORA-00069: cannot acquire lock -- table locks disabled for T

SCOTT@book> alter table t add v1 varchar2(10);
Table altered.
--//增加1列v1没有问题.

SCOTT@book> @ desc t
Name  Null?    Type
----- -------- ----------------------------
ID             NUMBER
V1             VARCHAR2(10)

SCOTT@book> alter table t drop column v1;
alter table t drop column v1
*
ERROR at line 1:
ORA-00069: cannot acquire lock -- table locks disabled for T
--//删除列不行.

SCOTT@book> alter table t set unused column v1;
alter table t set unused column v1
*
ERROR at line 1:
ORA-00069: cannot acquire lock -- table locks disabled for T

3.继续:
SCOTT@book> alter table t enable table lock;
Table altered.

SCOTT@book> alter table t set unused column v1;
Table altered.

--//有时候感觉oracle设计的很奇怪,也就是增加1列不需要TM锁吗?

3.继续测试:即使有事务存在的情况下.
--//session 1:
SCOTT@book> @ spid
       SID    SERIAL# PROCESS                  SERVER    SPID       PID  P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
        30        535 42553                    DEDICATED 42554       26        245 alter system kill session '30,535' immediate;

SCOTT@book> alter table t disable table lock;
Table altered.

--//session 2:
SCOTT@book> @ spid

SID    SERIAL# PROCESS                  SERVER    SPID       PID  P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
         1      10297 43346                    DEDICATED 43347       24        237 alter system kill session '1,10297' immediate;

SCOTT@book> insert into t values (2);
1 row created.

SCOTT@book> @ viewlock ;
   SID    SERIAL# USERNAME   OSUSER     MACHINE    MODULE       LOCK_TYPE       MODE_HELD  MODE_REQUE LOCK_ID1   LOCK_ID2   OWNER  OBJECT_TYP OBJECT_NAME          BLOCK LOCKWAIT
------ ---------- ---------- ---------- ---------- ------------ --------------- ---------- ---------- ---------- ---------- ------ ---------- -------------------- ----- --------------------
     1      10297 SCOTT      oracle     gxqyydg4   SQL*Plus     TX Transaction  Exclusive  None       655375     4583723                                           No

--//session 1:    
SCOTT@book> alter table t add v1 varchar2(10);
Table altered.

SCOTT@book> alter table t add v2 varchar2(10);
Table altered.

--//确实可以.
--//session 2:    
SCOTT@book> select * from t;
        ID V1         V2
---------- ---------- ----------
         1
         2

SCOTT@book> insert into t values (3);
insert into t values (3)
            *
ERROR at line 1:
ORA-00947: not enough values
--//增加了字段.

SCOTT@book> insert into t values (3,'a','b');
1 row created.

SCOTT@book> select * from t;
        ID V1         V2
---------- ---------- ----------
         1
         2
         3 a          b

4.如果enable table lock,如果有会话事务没有提交,在别的会话增加一列一定会挂起:
--//感觉oracle的设计还真奇怪....
--//session 1:
SCOTT@book>  alter table t enable table lock;
Table altered.

--//session 2:
SCOTT@book> insert into t values (4,'a','b');
1 row created.

--//session 1:
SCOTT@book> alter table t add v3 varchar2(10);
--//挂起!!

SCOTT@book> @ viewlock
   SID    SERIAL# USERNAME   OSUSER     MACHINE    MODULE       LOCK_TYPE       MODE_HELD  MODE_REQUE LOCK_ID1   LOCK_ID2   OWNER  OBJECT_TYP OBJECT_NAME          BLOCK LOCKWAIT
------ ---------- ---------- ---------- ---------- ------------ --------------- ---------- ---------- ---------- ---------- ------ ---------- -------------------- ----- --------------------
     1      10297 SCOTT      oracle     gxqyydg4   SQL*Plus     TM DML(TM)      Row-X (SX) None       42044813   0          SCOTT  TABLE      T                    No
     1      10297 SCOTT      oracle     gxqyydg4   SQL*Plus     TX Transaction  Exclusive  None       655379     4583660                                           Yes
    30        535 SCOTT      oracle     gxqyydg4   SQL*Plus     TX Transaction  None       Share      655379     4583660                                           No    0000000085439E00
    30        535 SCOTT      oracle     gxqyydg4   SQL*Plus     TM DML(TM)      Row-X (SX) None       42044813   0          SCOTT  TABLE      T                    No    0000000085439E00
    30        535 SCOTT      oracle     gxqyydg4   SQL*Plus     TX Transaction  Exclusive  None       589849     212173                                            No    0000000085439E00

5.viewlock.sql脚本:
$ cat viewlock.sql
column sid format 99999
column username format a10
column osuser format a10
column machine format a10
column lock_type format a15
column mode_held format a10
column mode_requested format a10
column lock_id1 format a10
column lock_id2 format a10
column owner format a6
column object_type format a10
column object_name format a20
column block format a5
column lockwait format a20

SELECT se.SID, se.serial#,se.username, se.osuser, se.machine,se.module,
       DECODE (lk.TYPE, 'TX', 'TX Transaction', 'TM', 'TM DML(TM)', 'UL', 'PL/SQL User Lock', lk.TYPE) lock_type,
       DECODE (lk.lmode,
               0, 'None',
               1, 'Null',
               2, 'Row-S (SS)',
               3, 'Row-X (SX)',
               4, 'Share',
               5, 'S/Row-X (SSX)',
               6, 'Exclusive',
               TO_CHAR (lk.lmode)
              ) mode_held,
       DECODE (lk.request,
               0, 'None',
               1, 'Null',
               2, 'Row-S (SS)',
               3, 'Row-X (SX)',
               4, 'Share',
               5, 'S/Row-X (SSX)',
               6, 'Exclusive',
               TO_CHAR (lk.request)
              ) mode_requested,
       TO_CHAR (lk.id1) lock_id1, TO_CHAR (lk.id2) lock_id2, ob.owner, ob.object_type, ob.object_name,
       DECODE (lk.BLOCK, 0, 'No', 1, 'Yes', 2, 'Global') BLOCK, se.lockwait
  FROM v$lock lk, dba_objects ob, v$session se
 WHERE lk.TYPE IN ('TX','TM', 'UL') AND lk.SID = se.SID AND lk.id1 = ob.object_id(+) order by 1;