declare
v_sql varchar2(200);
begin
loop
v_sql :='select seq1.nextval from dual';
execute immediate v_sql;
end loop;
end; SQL> select * from (select SAMPLE_TIME,
SESSION_ID,
NAME,
P1,
P2,
P3
from v$active_session_history ash, v$event_name enm
where ash.event# = enm.event#)
where rownum<10; 2 3 4 5 6 7 8 9 SAMPLE_TIME SESSION_ID NAME P1 P2 P3
--------------------------------------------------------------------------- ---------- ------------------------------ ---------- ---------- ----------
15-APR-14 07.24.15.366 PM 22 cursor: pin S 3155007310 75235328 196608
15-APR-14 07.24.13.356 PM 17 cursor: pin S 3155007310 2 196608
15-APR-14 07.24.09.356 PM 22 cursor: pin S 3155007310 75235329 589824
15-APR-14 07.24.07.346 PM 17 cursor: pin S 3155007310 75235328 196608
15-APR-14 07.24.04.346 PM 17 cursor: pin S 3155007310 2 589824
15-APR-14 07.24.03.336 PM 22 cursor: pin S 3155007310 75235328 196608
15-APR-14 07.24.01.336 PM 22 cursor: pin S 3155007310 75235328 196608
15-APR-14 07.24.00.336 PM 22 cursor: pin S 3155007310 1 589824
15-APR-14 07.23.56.326 PM 17 cursor: pin S 3155007310 75235330 589824 9 rows selected. P1 Hash value of cursor
P2 Mutex value (top 2 bytes contains SID holding mutex in exclusive mode, and bottom two bytes usually hold the value 0)
P3 Mutex where (an internal code locator) OR’d with Mutex Sleeps SELECT a.*, s.sql_text
FROM v$sql s,
(SELECT sid,
event,
wait_class,
p1 cursor_hash_value,
p2raw Mutex_value,
TO_NUMBER (SUBSTR (p2raw, 1, 8), 'xxxxxxxx') hold_mutex_x_sid
FROM v$session_wait
WHERE event LIKE 'cursor%') a
WHERE s.HASH_VALUE = a.p1 SQL> SELECT a.*, s.sql_text
FROM v$sql s,
(SELECT sid,
event,
wait_class,
p1 cursor_hash_value,
p2raw Mutex_value,
TO_NUMBER (SUBSTR (p2raw, 1, 8), 'xxxxxxxx') hold_mutex_x_sid
FROM v$session_wait
WHERE event LIKE 'cursor%') a
WHERE s.HASH_VALUE = 3155007310; 2 3 4 5 6 7 8 9 10 11 SID EVENT WAIT_CLASS CURSOR_HASH_VALUE MUTEX_VALUE HOLD_MUTEX_X_SID SQL_TEXT
---------- ------------------------------ ---------------------------------------------------------------- ----------------- ---------------- -------------- -- --------------------
1148 cursor: pin S Concurrency 3155007310 0000000000000002 0 select seq1.nextval from dual
当看到系统有很多session等待cursor: pin S事件的时候，要么是CPU不够快，要么是某个SQL的并行执行次数太多了而导致在child cursor上的mutex操作争用。如果是Capacity的问题，则可以升级硬件。如果是因为SQL的并行太多，则要么想办法降低该SQL执行次数，要么将该SQL复制成N个其它的SQL
cursor: pin S A session waits on this event when it wants to update a shared mutex pin and another session is currently in the process of updating a shared mutex pin for the same cursor object. This wait event should rarely be seen because a shared mutex pin update is very fast.(Wait Time: Microseconds)
Parameter Description P1 Hash value of cursor
P2 Mutex value (top 2 bytes contains SID holding mutex in exclusive mode, and bottom two bytes usually hold the value 0)
P3 Mutex where (an internal code locator) OR’d with Mutex Sleep