公众号：杨建荣的学习笔记 · 作者：笔记52天 · 发布：2014-04-24 09:55:46 · 原文链接

在数据库中，有时候需要删除用户，大多数时候都需要使用cascade选项，有些时候却不需要，想知道在这个简单的命令之后数据库倒底在干什么，
这时候给一些指定的操作加上trace就跟把那层纱窗揭开一样，可以很清楚看到数据库倒底在干些什么。
10046,sql_trace等都是一些不错的选择。
首先来复现一下这个问题。‘
创建一个新用户，然后马上删除。
SQL> create user jeanron identified by jeanron;
User created.

SQL> drop user jeanron;
User dropped.

###########################
可以看到删除是不需要cascade选项的。如果想加cascade选项，会不会有问题呢。
SQL> create user jeanron identified by jeanron;
User created.

SQL> drop user jeanron cascade;
User dropped.

###########################
可以看到是没有问题的，下面来复现ORA-01922这个错误。
SQL> create user jeanron identified by jeanron;
User created.

SQL> grant connect,resource to jeanron;
Grant succeeded.

SQL> conn jeanron/jeanron
Connected.
SQL> create table tt as select *from cat;
Table created.
SQL> conn / as sysdba
Connected.
SQL> drop user jeanron;
drop user jeanron
*
ERROR at line 1:
ORA-01922: CASCADE must be specified to drop ‘JEANRON’

############################
给这条命令做一个sql_trace，或者10046事件
如果在做sql_trace，10046事件的时候出现下面的情况。
SQL> alter session set sql_trace=true;
ERROR:
ORA-01031: insufficient privileges

SQL> alter session set events ‘10046 trace name context forever,level 12’;
ERROR:
ORA-01031: insufficient privileges

只需要赋予alter session的权限就可以了。
SQL> grant alter session to jeanron;
Grant succeeded.

SQL> alter session set events ‘10046 trace name context forever,level 12’;
Session altered.

SQL> drop user jeanron;
drop user jeanron
*
ERROR at line 1:
ORA-01922: CASCADE must be specified to drop ‘JEANRON’

SQL> alter session set events ‘10046 trace name context off’;
Session altered.
在trace目录下找到最新的trace日志，使用tkprof来格式化一下。
[ora11g@rac1 trace]$ tkprof TEST01_ora_5888.trc
output = b.log
TKPROF: Release 11.2.0.3.0 – Development on Wed Apr 23 07:42:26 2014
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.

可以看到格式化之后的日志文件内容就比较清晰了。可以在开头就看到如下的一段，命令开始了。
SQL ID: 6vu28ambaxjjh Plan Hash: 0
drop user jeanron

call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
——- —— ——– ———- ———- ———- ———- ———-
total 2 0.00 0.00 0 0 0 0

Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS

Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
—————————————- Waited ———- ————
SQL*Net break/reset to client 2 0.00 0.00
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 13.27 13.27
********************************************************************************

…..
如下的部分就是一些相应的递归sql。
select user#,password,datats#,tempts#,type#,defrole,resource$, ptime,
decode(defschclass,NULL,’DEFAULT_CONSUMER_GROUP’,defschclass),spare1,spare4,
ext_username,spare2
from
user$ where name=:1

call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 2 0 1
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.00 0.00 0 2 0 1

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: SYS (recursive depth: 1)
Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max) Row Source Operation
———- ———- ———- —————————————————
1 1 1 TABLE ACCESS BY INDEX ROWID USER$ (cr=2 pr=0 pw=0 time=152 us cost=1 size=101 card=1)
1 1 1 INDEX UNIQUE SCAN I_USER1 (cr=1 pr=0 pw=0 time=98 us cost=0 size=0 card=1)(object id 46)

********************************************************************************

可以看到在最后面有这样一条sql的信息。
SQL ID: 8mj6vafkkhyr4 Plan Hash: 310931108

select null
from
obj$ where owner#=:1 and type#!=10 union all select null from link$ where
owner#=:1 union all select null from streams$_capture_process where
capture_userid=:1 union all select null from streams$_apply_process where
apply_userid=:1 union all select null from wri$_sqlset_definitions s,user$
u where s.owner = u.name and u.user#=:1 union all select null from
wri$_adv_tasks where owner#=:1

call count cpu elapsed disk query current rows
——- —— ——– ———- ———- ———- ———- ———-
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 0.00 0.00 0 41 0 1
——- —— ——– ———- ———- ———- ———- ———-
total 3 0.00 0.00 0 41 0 1

Misses in library cache during parse: 0
Optimizer mode: CHOOSE
Parsing user id: SYS (recursive depth: 1)
Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max) Row Source Operation
———- ———- ———- —————————————————
1 1 1 UNION-ALL (cr=41 pr=0 pw=0 time=2554 us)
1 1 1 INDEX FAST FULL SCAN I_OBJ1 (cr=41 pr=0 pw=0 time=2510 us cost=12 size=10367 card=1481)(object id 36)
0 0 0 INDEX RANGE SCAN I_LINK1 (cr=0 pr=0 pw=0 time=0 us cost=0 size=13 card=1)(object id 138)
0 0 0 TABLE ACCESS FULL STREAMS$_CAPTURE_PROCESS (cr=0 pr=0 pw=0 time=0 us cost=2 size=13 card=1)
0 0 0 TABLE ACCESS FULL STREAMS$_APPLY_PROCESS (cr=0 pr=0 pw=0 time=0 us cost=2 size=13 card=1)
0 0 0 NESTED LOOPS (cr=0 pr=0 pw=0 time=0 us)
0 0 0 NESTED LOOPS (cr=0 pr=0 pw=0 time=0 us cost=0 size=34 card=1)
0 0 0 INDEX FULL SCAN WRI$_SQLSET_DEFINITIONS_IDX_01 (cr=0 pr=0 pw=0 time=0 us cost=0 size=17 card=1)(object id 6242)
0 0 0 INDEX UNIQUE SCAN I_USER1 (cr=0 pr=0 pw=0 time=0 us cost=0 size=0 card=1)(object id 46)
0 0 0 TABLE ACCESS BY INDEX ROWID USER$ (cr=0 pr=0 pw=0 time=0 us cost=0 size=17 card=1)
0 0 0 INDEX RANGE SCAN WRI$_ADV_TASKS_IDX_02 (cr=0 pr=0 pw=0 time=0 us cost=1 size=38 card=19)(object id 5811)
自己好好琢磨了下，这里面还这有些文章。它会从回收站，各数据字典基表中查询是否有相应的Object和db link,stream对象。
为了方便查看起见，我把sql整理了一下，可以用如下的方式。如果有返回结果，说明需要cascade选项。
column userid new_value userid format 999999;
select user# userid from user$ where name=’A’;
select ‘drop user need cascade option’
from
obj$ where owner#=&userid and type#!=10
union all
select ‘drop user need cascade option’ from link$ where
owner#=&userid
union all
select ‘drop user need cascade option’ from streams$_capture_process where
capture_userid=&userid
union all
select ‘drop user need cascade option’ from streams$_apply_process where
apply_userid=&userid
union all
select ‘drop user need cascade option’ from wri$_sqlset_definitions s,user$
u where s.owner = u.name and u.user#=&userid
union all
select ‘drop user need cascade option’ from
wri$_adv_tasks where owner#=&userid
/

N
–

如果返回now rows selected 就表明不需要cascade.
SQL> select ‘drop user need cascade option’
2 from
3 obj$ where owner#=&userid and type#!=10
4 union all
5 select ‘drop user need cascade option’ from link$ where
6 owner#=&userid
7 union all
8 select ‘drop user need cascade option’ from streams$_capture_process where
9 capture_userid=&userid
10 union all
11 select ‘drop user need cascade option’ from streams$_apply_process where
12 apply_userid=&userid
13 union all
14 select ‘drop user need cascade option’ from wri$_sqlset_definitions s,user$
15 u where s.owner = u.name and u.user#=&userid
16 union all
17 select ‘drop user need cascade option’ from
18 wri$_adv_tasks where owner#=&userid
19 /
old 3: obj$ where owner#=&userid and type#!=10
new 3: obj$ where owner#= 53 and type#!=10
old 6: owner#=&userid
new 6: owner#= 53
old 9: capture_userid=&userid
new 9: capture_userid= 53
old 12: apply_userid=&userid
new 12: apply_userid= 53
old 15: u where s.owner = u.name and u.user#=&userid
new 15: u where s.owner = u.name and u.user#= 53
old 18: wri$_adv_tasks where owner#=&userid
new 18: wri$_adv_tasks where owner#= 53

no rows selected