[20150304]唯一索引与阻塞.txt

--昨天帮别人定位一个唯一索引导致出现ora-00001的问题，实际上很简单，程序使用max(id)取得最大号，然后插入，这样的结果在业务
--高峰，出现阻塞或者ora-00001错误。我仅仅简单做一下跟踪很容易定位这个问题。

--换一个角度，使用别的方法是否可行呢，自己做一个例子来验证看看。

1.建立测试环境：

SCOTT@test> create table t as select rownum id,cast ( 'test' as varchar2(10)) name from dual connect by levelTable created.

SCOTT@test> create unique index  i_t_id on t(id);
Index created.

2.测试：
--session 1,插入不提交:
SCOTT@test> insert into t values (11,'a');
1 row created.

--session 2:
SCOTT@test> insert into t values (11,'b');

--出现阻塞情况，如果会话1提交，会报ora-00001错误。

3.分析：

$ cat viewlock.sql
column sid format 99999
column username format a10
column osuser format a10
column machine format a10
column lock_type format a12
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,
       DECODE (lk.TYPE, 'TX', 'Transaction', '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(+);

SCOTT@test> @viewlock ;

SID    SERIAL# USERNAME   OSUSER     MACHINE    LOCK_TYPE    MODE_HELD  MODE_REQUE LOCK_ID1   LOCK_ID2   OWNER  OBJECT_TYP OBJECT_NAME          BLOCK LOCKWAIT
------ ---------- ---------- ---------- ---------- ------------ ---------- ---------- ---------- ---------- ------ ---------- -------------------- ----- --------------------
   401         15 SCOTT      oracle11g  hisdg      DML(TM)      Row-X (SX) None       300095     0          SCOTT  TABLE      T                    No    00000000BDC92778
   597         65 SCOTT      oracle11g  hisdg      DML(TM)      Row-X (SX) None       300095     0          SCOTT  TABLE      T                    No
   597         65 SCOTT      oracle11g  hisdg      Transaction  Exclusive  None       1835029    71                                                Yes
   401         15 SCOTT      oracle11g  hisdg      Transaction  None       Share      1835029    71                                                No    00000000BDC92778
   401         15 SCOTT      oracle11g  hisdg      Transaction  Exclusive  None       851975     1740                                              No    00000000BDC92778

--注意看阻塞的LOCK_ID1=1835029,LOCK_ID2=71. 这个LOCK_ID1 前16位表示事务的 XIDUSN，后16位表示XIDSLOT。可以做一个简单计算。

SCOTT@test> select trunc(1835029/power(2,16)),mod(1835029,power(2,16)) from dual;
TRUNC(1835029/POWER(2,16)) MOD(1835029,POWER(2,16))
-------------------------- ------------------------
                        28                       21

SCOTT@test> host cat xid.sql
select dbms_transaction.local_transaction_id()  x from dual ;
select XIDUSN,XIDSLOT,XIDSQN,UBAFIL,UBABLK,UBAREC, UBASQN,STATUS,used_ublk,USED_UREC,xid,ADDR  from v$transaction;

SCOTT@test> @xid
X
------------------------------

XIDUSN    XIDSLOT     XIDSQN     UBAFIL     UBABLK     UBAREC     UBASQN STATUS            USED_UBLK  USED_UREC XID              ADDR
---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- ---------- ---------- ---------------- ----------------
        28         21         71          3      11125         10         83 ACTIVE                    1          2 1C00150047000000 00000000BBF2E4A0
        13          7       1740          3      13079         15        523 ACTIVE                    1          1 0D000700CC060000 00000000B81C13B0

--可以发现正好对上。

SCOTT@test> select sid,serial# from v$session where taddr='00000000BBF2E4A0';
   SID    SERIAL#
------ ----------
   597         65

--这些信息都正好对上。

4.然后做一个转储看看：

SCOTT@test> alter system dump datafile 3 block 11125;
System altered.

..
*-----------------------------
* Rec #0xa  slt: 0x15  objn: 300096(0x00049440)  objd: 300096  tblspc: 4(0x00000004)
*       Layer:  10 (Index)   opc: 22   rci 0x09
Undo type:  Regular undo   Last buffer split:  No
Temp Object:  No
Tablespace Undo:  No
rdba: 0x00000000
*-----------------------------
index undo for leaf key operations
KTB Redo
op: 0x04  ver: 0x01
compat bit: 4 (post-11) padding: 1
op: L  itl: xid:  0xffff.000.00000000 uba: 0x00000000.0000.00
                      flg: C---    lkc:  0     scn: 0x0002.cb8eb5e2
Dump kdilk : itl=2, kdxlkflg=0x1 sdc=42 indexid=0x1000722 block=0x01000723
(kdxlpu): purge leaf row
key :(3):  02 c1 0c

SCOTT@test> select name from sys.undo$ where us#=28;
NAME
---------------------
_SYSSMU28_3223209608$

SCOTT@test> ALTER SYSTEM DUMP UNDO BLOCK '_SYSSMU28_3223209608$' XID 28  21 71;
System altered.

********************************************************************************
Undo Segment:  _SYSSMU28_3223209608$ (28)
xid: 0x001c.015.00000047
Low Blk   :   (0, 0)
High Blk  :   (2, 127)
Object Id :   ALL
Layer     :   ALL
Opcode    :   ALL
Level     :   2

********************************************************************************
UNDO BLK:  Extent: 2   Block: 117   dba (file#, block#): 3,0x00002b75
xid: 0x001c.015.00000047  seq: 0x53  cnt: 0xa   irb: 0xa   icl: 0x0   flg: 0x0000

Rec Offset      Rec Offset      Rec Offset      Rec Offset      Rec Offset
---------------------------------------------------------------------------
0x01 0x1f34     0x02 0x1e8c     0x03 0x1d90     0x04 0x1d28     0x05 0x1cd0
0x06 0x1be4     0x07 0x1b3c     0x08 0x1a5c     0x09 0x19d4     0x0a 0x1978

*-----------------------------
* Rec #0xa  slt: 0x15  objn: 300096(0x00049440)  objd: 300096  tblspc: 4(0x00000004)
*       Layer:  10 (Index)   opc: 22   rci 0x09
Undo type:  Regular undo   Last buffer split:  No
Temp Object:  No
Tablespace Undo:  No
rdba: 0x00000000
*-----------------------------
index undo for leaf key operations
KTB Redo
op: 0x04  ver: 0x01
compat bit: 4 (post-11) padding: 1
op: L  itl: xid:  0xffff.000.00000000 uba: 0x00000000.0000.00
                      flg: C---    lkc:  0     scn: 0x0002.cb8eb5e2
Dump kdilk : itl=2, kdxlkflg=0x1 sdc=42 indexid=0x1000722 block=0x01000723
(kdxlpu): purge leaf row
key :(3):  02 c1 0c

*-----------------------------
* Rec #0x9  slt: 0x15  objn: 300095(0x0004943f)  objd: 300095  tblspc: 4(0x00000004)
*       Layer:  11 (Row)   opc: 1   rci 0x00
Undo type:  Regular undo    Begin trans    Last buffer split:  No
Temp Object:  No
Tablespace Undo:  No
rdba: 0x00000000Ext idx: 0
flg2: 0
*-----------------------------
uba: 0x00c02b75.0053.08 ctl max scn: 0x0002.cb8e8911 prv tx scn: 0x0002.cb8e8914
txn start scn: scn: 0x0002.cb8eb610 logon user: 84
prev brb: 12594031 prev bcl: 0
KDO undo record:
KTB Redo
op: 0x03  ver: 0x01
compat bit: 4 (post-11) padding: 1
op: Z
KDO Op code: DRP row dependencies Disabled
  xtype: XA flags: 0x00000000  bdba: 0x0100071f  hdba: 0x0100071a
itli: 1  ispac: 0  maxfr: 4858
tabn: 0 slot: 0(0x0)

+++++++++++ Next block not in extent map - rollback segment has been shrunk.
+ WARNING + Block dba (file#, block#): 0,0x00000000
+++++++++++

*************************************
Total undo blocks scanned  = 1
Total undo records scanned = 2
Total undo blocks dumped   = 1
Total undo records dumped  = 2

##Total warnings issued = 1
*************************************

--插入索引的objd: 300096，indexid=0x1000722 block=0x01000723

SCOTT@test> select object_name from dba_objects where owner=user and data_object_id=300096;
OBJECT_NAME
--------------------
I_T_ID

SCOTT@test> set verify off
SCOTT@test> @dfb 1000723
    RFILE#     BLOCK#
---------- ----------
         4       1827

TEXT
-----------------------------------------
alter system dump datafile 4 block 1827 ;

SCOTT@test> select * from dba_extents where owner=user and segment_name='I_T_ID';
OWNER  SEGMENT_NAME   SEGMENT_TYPE  TABLESPACE_NAME    EXTENT_ID    FILE_ID   BLOCK_ID      BYTES     BLOCKS RELATIVE_FNO
------ -------------  ------------- ----------------- ---------- ---------- ---------- ---------- ---------- ------------
SCOTT  I_T_ID         INDEX         USERS                      0          4       1824      65536          8            4

SCOTT@test> select HEADER_FILE,HEADER_BLOCK,BYTES,BLOCKS,EXTENTS,INITIAL_EXTENT,NEXT_EXTENT from dba_segments where owner=user and segment_name='I_T_ID';
HEADER_FILE HEADER_BLOCK      BYTES     BLOCKS    EXTENTS INITIAL_EXTENT NEXT_EXTENT
----------- ------------ ---------- ---------- ---------- -------------- -----------
          4         1826      65536          8          1          65536     1048576

--正好是块头的下1块，1827.当然这样定位有点麻烦，了解许多知识点还是很用帮助的。