检查数据库是否存在锁信息，在查询V$LOCK视图时发现很长时间没有响应，甚至一度认为数据库HANG住：
SQL> select * from v$lock where type != 'MR';
ADDR KADDR SID TY ID1 ID2 LMODE REQUEST CTIME BLOCK
---------------- ---------------- ---- -- -------- ---- ----- ------- ----- -----
0000000C5A6AA770 0000000C5A6AA7C8 3405 TO 5124 2 3 0 8543 0
0000000C5A6AAA10 0000000C5A6AAA68 3405 TO 5124 1 3 0 8543 0
00007FEEB24CBDE8 00007FEEB24CBE48 4255 TM 5124 0 3 0 5455 0
0000000C5A6A4860 0000000C5A6A48B8 1 AE 100 0 4 0 10323 0
00007FEEB24CBDE8 00007FEEB24CBE48 1144 TM 5124 0 3 0 107 0
0000000C5A6A9DD0 0000000C5A6A9E28 1144 TO 5124 2 3 0 107 0
0000000C44D8FF08 0000000C44D8FF80 1144 TX 12845057 2063 6 0 107 0
0000000C5A6AA4D0 0000000C5A6AA528 3405 AE 100 0 4 0 9547 0
0000000C4F97CC28 0000000C4F97CCA0 3405 TX 12517398 2118 6 0 8543 0
0000000C5A6A2278 0000000C5A6A22D0 3680 RS 25 1 2 0 10346 0
0000000C5A6A3790 0000000C5A6A37E8 3963 TS 16 1 3 0 8906 0
0000000C5A6AACC8 0000000C5A6AAD20 4255 AE 100 0 4 0 5484 0
0000000C4FDC1288 0000000C4FDC1300 4255 TX 15073308 1757 6 0 5455 0
0000000C5A6AA850 0000000C5A6AA8A8 1144 TO 5124 1 3 0 7441 0
0000000C5A6A9338 0000000C5A6A9390 1420 TO 5124 2 3 0 840 0
0000000C5A6A4940 0000000C5A6A4998 1983 KD 0 0 6 0 10324 0
0000000C5A6A4B00 0000000C5A6A4B58 1983 KT 12540 0 4 0 10324 0
0000000C5A6A2198 0000000C5A6A21F0 3680 CF 0 0 2 0 10350 0
0000000C5A6A2438 0000000C5A6A2490 3397 RT 1 0 6 0 10346 0
0000000C5A6A1E18 0000000C5A6A1E70 3680 XR 4 0 1 0 10350 0
0000000C5A6A5F38 0000000C5A6A5F90 1134 AE 100 0 4 0 109 0
0000000C5A6A4E80 0000000C5A6A4ED8 1420 AE 100 0 4 0 2824 0
0000000C4FCAB578 0000000C4FCAB5F0 1420 TX 10223617 2128 6 0 840 0
0000000C5A6A9EB0 0000000C5A6A9F08 1420 TO 5124 1 3 0 840 0
0000000C5A6AA690 0000000C5A6AA6E8 4255 TO 5124 2 3 0 5455 0
00007FEEB24CBDE8 00007FEEB24CBE48 1420 TM 5124 0 3 0 840 0
0000000C5A6A6018 0000000C5A6A6070 1990 AE 100 0 4 0 1489 0
0000000C5A6A4A20 0000000C5A6A4A78 2831 PW 1 0 3 0 10323 0
0000000C5A6A1EF8 0000000C5A6A1F50 3680 RD 1 0 1 0 10350 0
0000000C5A6AA5B0 0000000C5A6AA608 1144 AE 100 0 4 0 7459 0
00007FEEB24CBDE8 00007FEEB24CBE48 3405 TM 5124 0 3 0 8543 0
0000000C5A6A2518 0000000C5A6A2570 3963 TS 3 1 3 0 10325 0
0000000C5A6AB128 0000000C5A6AB180 4255 TO 5124 1 3 0 5455 0
33 rows selected.
Elapsed: 00:13:13.74
一个如此简单的查询执行时间居然超过了13分钟，在这个SQL运行过程中检查发现，这个会话在等待直接路径写：
SQL> select sql_text from v$sql where sql_id in （select sql_id from v$Session where sid = 1420）；
SQL_TEXT
--------------------------------------------------------------------------------------
SELECT * FROM V$LOCK WHERE TYPE != :"SYS_B_0"
SQL> select event, p1text, p1 from v$session where sid = 1420;
EVENT P1TEXT P1
---------------------------------------- --------------- ----------
direct path write temp file number 201
检查了一下执行计划：
SQL> explain plan for
2 SELECT * FROM V$LOCK WHERE TYPE != 'MR';
Explained.
SQL> select * from table（dbms_XPlan.display）；
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------
Plan hash value: 1899724433
-------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost （%CPU）| Time |
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 158 | 1 （100）| 00:00:01 |
|* 1 | HASH JOIN | | 1 | 158 | 1 （100）| 00:00:01 |
| 2 | MERGE JOIN CARTESIAN | | 5 | 400 | 0 （0）| 00:00:01 |
| 4 | BUFFER SORT | | 5 | 240 | 0 （0）| 00:00:01 |
|* 5 | FIXED TABLE FULL | X$KSQRS | 5 | 240 | 0 （0）| 00:00:0