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分类: Oracle

2009-06-03 10:18:29

Enqueues are sophisticated locks for managing access to shared resources
(like tables, rows, jobs, redo threads). An enqueue can be requested in
different levels/mode: null, row share, row exclusive, share, share row
exclusive or exclusive. If a session holds an enqueue in share mode, other
sessions can then also take the enqueue in share mode (for the same resource).
If a session holds an enqueue in exclusive mode, other sessions that wants to
get it - independently in which level - they have to wait.
 
等待事件:enqueue是串行访问不同资源的本地锁。这种等待事件说明等待一个正被另一个session持有的排它模式或请求模式锁。
enqueue通常描述成这种格式:TYPE-ID1-ID2
"TYPE" is a 2 character text string
"ID1" is a 4 byte hexadecimal number
"ID2" is a 4 byte hexadecimal number
Convert P1 into hexadecimal (or use P1RAW) and extract the lock type and requested mode from this by converting the
first 2 bytes of the hexadecimal number to ASCII and the second 2 bytes to a number:
SELECT chr(to_char(bitand(p1,-16777216))/16777215)||
         chr(to_char(bitand(p1, 16711680))/65535) "Lock",
         to_char( bitand(p1, 65535) )    "Mode"
    FROM v$session_wait
   WHERE event = 'enqueue';
 
SELECT DECODE(request,0,'Holder: ','Waiter: ')||sid sess,
         id1, id2, lmode, request, type
    FROM V$LOCK
   WHERE (id1, id2, type) IN
             (SELECT id1, id2, type FROM V$LOCK WHERE request>0)
   ORDER BY id1, request;

查看等待时间最长的enqueue的等待事件
SELECT  eq_type "Lock",
          total_req# "Gets",
          total_wait# "Waits",
   cum_wait_time
    FROM V$enqueue_stat
    WHERE Total_wait# > 0
    order by 4 desc;
 
 
记录一个enqueue等待事件的case,原因是由于前一次刷新被异常终止,后台线程没有被释放造成的.
锁类型:JI是物化视图刷新时产生的一个种锁.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
SQL> SELECT chr(to_char(bitand(p1,-16777216))/16777215)||
  2           chr(to_char(bitand(p1, 16711680))/65535) "Lock",
  3           to_char( bitand(p1, 65535) )    "Mode"
  4      FROM v$session_wait
  5     WHERE event = 'enqueue';
Lo Mode                                                                        
-- ----------------------------------------                                    
JI 6                                                                           
SQL> SELECT * FROM v$lock WHERE request > 0;
ADDR     KADDR           SID TY        ID1        ID2      LMODE    REQUEST    
-------- -------- ---------- -- ---------- ---------- ---------- ----------    
     CTIME      BLOCK                                                          
---------- ----------                                                          
44D05F70 44D05F80        218 JI       7895          0          0          6    
         3          0                                                          
                                                                               
SQL> SELECT DECODE(request,0,'Holder: ','Waiter: ')||sid sess,
  2           id1, id2, lmode, request, type
  3      FROM V$LOCK
  4     WHERE (id1, id2, type) IN
  5               (SELECT id1, id2, type FROM V$LOCK WHERE request>0)
  6     ORDER BY id1, request;
SESS                                                    ID1        ID2         
------------------------------------------------ ---------- ----------         
     LMODE    REQUEST TY                                                       
---------- ---------- --                                                       
Holder: 166                                            7895          0         
         6          0 JI                                                       
                                                                               
Waiter: 218                                            7895          0         
         0          6 JI                                                       
                                                                               
SQL> SELECT  eq_type "Lock",
  2            total_req# "Gets",
  3            total_wait# "Waits",
  4     cum_wait_time
  5      FROM V$enqueue_stat
  6      WHERE Total_wait# > 0
  7      order by 4 desc;
Lo       Gets      Waits CUM_WAIT_TIME                                         
-- ---------- ---------- -------------                                         
JI      53066      22865     117531891                                         
TM    8337334          8       1105389                                         
CF     927241        387         68069                                         
TX   10480779       1225         59699                                         
TC        320         64         32454                                         
CI     154944         31          6659                                         
SQ     434743        659           766                                         
US       6153          6           156                                         
HW     191455          2            16                                         
CU     136672          4             0                                         
IA          2          1             0                                         
Lo       Gets      Waits CUM_WAIT_TIME                                         
-- ---------- ---------- -------------                                         
PS         50          1             0                                         
JD     374791          2             0                                         
13 rows selected.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
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