Oracle技术之flashback drop与索引
今天在跟朋友讨论了如下话题：
《有一张表上建立索引，DROP该表，又闪回删除回来，请问，这张表上的索引还能用吗？如果有变化那是什么？》
我进行了如下测试：
sys@MAA> select * from v$version;
BANNER
----------------------------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE 11.2.0.3.0 Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
-- 我的TEST2表上有两个索引
luocs@MAA> select index_name, status from user_indexes where table_name='TEST2';
INDEX_NAME STATUS
------------------------------------------------------------ ----------------
INX_TEST2_ZH VALID
INX_TEST2 VALID
luocs@MAA> set autot trace exp stat
luocs@MAA> select count(*) from test2 where id=1;
Execution Plan
----------------------------------------------------------
Plan hash value: 3565898414
----------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 5 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 5 | | |
|* 2 | INDEX RANGE SCAN| INX_TEST2_ZH | 2 | 10 | 2 (0)| 00:00:01 |
----------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ID"=1)
Statistics
----------------------------------------------------------
1 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
525 bytes sent via SQL*Net to client
523 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
-- DROP 表TEST2
luocs@MAA> drop table test2;
Table dropped.
-- 索引也被删除
luocs@MAA> select index_name, status from user_indexes where table_name='TEST2';
no rows selected
-- 这时候查看回收站，我们看到表的删除记录，却没有看到索引的
luocs@MAA> show recyclebin
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
TEST2 BIN$048hXdZTf0HgQwEAAH/4UQ==$0 TABLE 2013-01-18:19:20:06
-- 进行闪回删除
luocs@MAA> flashback table test2 to before drop;
Flashback complete.
-- 这时候又能看到索引信息，也是可用状态，却索引名称改变，依然使用回收站里的名字
luocs@MAA> select index_name, status from user_indexes where table_name='TEST2';
INDEX_NAME STATUS
------------------------------------------------------------ ----------------
BIN$048hXdZSf0HgQwEAAH/4UQ==$0 VALID
BIN$048hXdZRf0HgQwEAAH/4UQ==$0 VALID
-- 我们也看到该索引能够正常使用
luocs@MAA> set autot trace exp
luocs@MAA> select count(*) from test2 where id=1;
Execution Plan
----------------------------------------------------------
Plan hash value: 3980542661
----------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
----------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 5 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 5 | | |
|* 2 | INDEX RANGE SCAN| BIN$048hXdZSf0HgQwEAAH/4UQ==$0 | 2 | 10 | 2 (0)| 00:00:01 |
----------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("ID"=1)
-- 我们可以RENAME索引名字以恢复
luocs@MAA> alter index "BIN$048hXdZSf0HgQwEAAH/4UQ==$0" rename to inx_test2_zh;
Index altered.
luocs@MAA> alter index "BIN$048hXdZRf0HgQwEAAH/4UQ==$0" rename to inx_test2;
Index altered.
luocs@MAA> select index_name, status from user_indexes where table_name='TEST2';
INDEX_NAME STATUS
------------------------------------------------------------ ----------------
INX_TEST2_ZH VALID
INX_TEST2 VALID
因此，在表被DROP掉后，索引也被放到回收站里，再我们flashback drop之后，索引也被还原，也能正常使用，但索引名却没有还原过来。
那这里有个问题存在，既然索引页被放到回收站里，为什么执行show recyclebin的时候没有看到索引信息？
OK，我通过如下方式解释：
-- 通过10046事件分析下show recyclebin到底干了什么
luocs@MAA> alter session set events '10046 trace name context forever, level 8';
Session altered.
luocs@MAA> show recyclebin
luocs@MAA> alter session set events '10046 trace name context off';
Session altered.
luocs@MAA> select value from v$diag_info where name = 'Default Trace File';
VALUE
----------------------------------------------------------------------------------------------------
/u01/app/oracle/diag/rdbms/maa/maa/trace/maa_ora_32580.trc
-- 我在TRACE内容里找到如下语句，这里重点看WHERE子句CAN_UNDROP='YES'
SELECT ORIGINAL_NAME ORIGNAME_PLUS_SHOW_RECYC,OBJECT_NAME
OBJECTNAME_PLUS_SHOW_RECYC,TYPE OBJTYPE_PLUS_SHOW_RECYC,DROPTIME
DROPTIME_PLUS_SHOW_RECYC
FROM
USER_RECYCLEBIN WHERE CAN_UNDROP='YES' ORDER BY ORIGINAL_NAME,DROPTIME DESC,
OBJECT_NAME
-- 这里CAN_UNDROP='YES' 起到作用了
-- 我们看一下recyclebin$表创建语法与注释信息(Oracle 11g开始recyclebin$表创建语句在dsqlddl.bsq脚本里，位于$ORACLE_HOME/rdbms/admin)
create table recyclebin$
(
obj# number not null, /* original object number */
owner# number not null, /* owner user number */
original_name varchar2(32), /* Original Object Name */
operation number not null, /* Operation carried out */
/* 0 -> DROP */
/* 1 -> TRUNCATE (not supported) */
type# number not null, /* object type (see KQD.H) */
ts# number, /* tablespace number */
file# number, /* segment header file number */
block# number, /* segment header block number */
droptime date, /* time when object was dropped */
dropscn number, /* SCN of Tx which caused the drop */
partition_name varchar2(32), /* Name of the partition dropped */
/* NULL otherwise */
flags number, /* flags for undrop processing */
related number not null, /* obj one level up in heirarchy */
bo number not null, /* base object */
purgeobj number not null, /* obj to purge when purging this */
base_ts# number, /* Base objects Tablespace number */
base_owner# number, /* Base objects owner number */
space number, /* number of blocks used by the object */
con# number, /* con#, if index is due to constraint */
spare1 number,
spare2 number,
spare3 number
)
/
-- 其中flags的注释内容是flags for undrop processing，我们可以查这张表，然后查看表和索引对应的flags分别多少
-- 再drop 表test2，然后查看recyclebin$表
sys@MAA> select USER_ID, USERNAME from dba_users where USERNAME='LUOCS';
USER_ID USERNAME
---------- ------------------------------------------------------------
51 LUOCS
sys@MAA> select OBJ#, OWNER#, TYPE#, OPERATION, DROPTIME, DROPSCN, FLAGS from recyclebin$ where OWNER#=51;
OBJ# OWNER# TYPE# OPERATION DROPTIME DROPSCN FLAGS
---------- ---------- ---------- ---------- ----------------------- ---------- ----------
24248 51 2 0 18-JAN-2013 21:02:24 1134044 18
24352 51 2 0 18-JAN-2013 21:02:24 1134047 18
24247 51 1 0 18-JAN-2013 21:02:24 1134051 30
-- 可知表对应的flags为30，索引对应的flags为18。另外，OBJ#为DROP对象前的对象编号，这个在下面闪回删除之后再证明
OK 有点跑偏了。
-- 我们通过10046分析出show recyclebin其实是执行下面一段SQL语句：
SELECT ORIGINAL_NAME ORIGNAME_PLUS_SHOW_RECYC,OBJECT_NAME
OBJECTNAME_PLUS_SHOW_RECYC,TYPE OBJTYPE_PLUS_SHOW_RECYC,DROPTIME
DROPTIME_PLUS_SHOW_RECYC
FROM
USER_RECYCLEBIN WHERE CAN_UNDROP='YES' ORDER BY ORIGINAL_NAME,DROPTIME DESC,
OBJECT_NAME
-- 我们将CAN_UNDROP='YES'去掉，然后执行：
luocs@MAA> SELECT ORIGINAL_NAME ORIGNAME_PLUS_SHOW_RECYC,OBJECT_NAME
2 OBJECTNAME_PLUS_SHOW_RECYC,TYPE OBJTYPE_PLUS_SHOW_RECYC,DROPTIME
3 DROPTIME_PLUS_SHOW_RECYC
4 FROM
5 USER_RECYCLEBIN ORDER BY ORIGINAL_NAME,DROPTIME DESC,
6 OBJECT_NAME
7 /
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
INX_TEST2 BIN$05C5BoYUf0TgQwEAAH+5aw==$0 INDEX 2013-01-18:21:02:24
INX_TEST2_ZH BIN$05C5BoYVf0TgQwEAAH+5aw==$0 INDEX 2013-01-18:21:02:24
TEST2 BIN$05C5BoYWf0TgQwEAAH+5aw==$0 TABLE 2013-01-18:21:02:24
-- 从这里我们也获得了原对象名以及回收站里的对象名，因此RENAME的时候可以找对对象。
-- 将CAN_UNDROP 设置为 'NO'再执行：
luocs@MAA> SELECT ORIGINAL_NAME ORIGNAME_PLUS_SHOW_RECYC,OBJECT_NAME
2 OBJECTNAME_PLUS_SHOW_RECYC,TYPE OBJTYPE_PLUS_SHOW_RECYC,DROPTIME
3 DROPTIME_PLUS_SHOW_RECYC
4 FROM
5 USER_RECYCLEBIN WHERE CAN_UNDROP='NO' ORDER BY ORIGINAL_NAME,DROPTIME DESC,
6 OBJECT_NAME
7 /
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
INX_TEST2 BIN$05C5BoYUf0TgQwEAAH+5aw==$0 INDEX 2013-01-18:21:02:24
INX_TEST2_ZH BIN$05C5BoYVf0TgQwEAAH+5aw==$0 INDEX 2013-01-18:21:02:24
-- 进行flashback drop
luocs@MAA> flashback table test2 to before drop;
Flashback complete.
-- 再查询已经看不到内容了
luocs@MAA> SELECT ORIGINAL_NAME ORIGNAME_PLUS_SHOW_RECYC,OBJECT_NAME
2 OBJECTNAME_PLUS_SHOW_RECYC,TYPE OBJTYPE_PLUS_SHOW_RECYC,DROPTIME
3 DROPTIME_PLUS_SHOW_RECYC
4 FROM
5 USER_RECYCLEBIN ORDER BY ORIGINAL_NAME,DROPTIME DESC,
6 OBJECT_NAME
7 /
no rows selected
-- 根据上面获得的对象编号来查看对象名字
sys@MAA> col OBJECT_NAME for a30
sys@MAA> col OWNER for a30
sys@MAA> select OBJECT_NAME, OWNER from dba_objects where OBJECT_ID IN ('24248','24352','24247');
OBJECT_NAME OWNER
------------------------------ ------------------------------
BIN$048hXdZVf0HgQwEAAH/4UQ==$1 LUOCS
BIN$048hXdZUf0HgQwEAAH/4UQ==$1 LUOCS
TEST2 LUOCS
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