[20160302]奇怪的回滚段.txt

--昨天在探究oracle的启动时，无意中发现我安装这个版本，在安装的测试样例表空间example出现回滚段。
--自己今天仔细看看：

1.环境：
SYS@book> @ &r/ver1

PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

SYS@book> column name format a22
SYS@book> select us#,name,user#,file#,BLOCK#,SCNBAS,SCNWRP,XACTSQN,UNDOSQN,INST#,STATUS$,TS#,FLAGS,SPARE1 from undo$;
US# NAME                   USER#      FILE#     BLOCK#     SCNBAS     SCNWRP    XACTSQN    UNDOSQN      INST#    STATUS$        TS#      FLAGS     SPARE1
---- ---------------------- ----- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------- ----------
   0 SYSTEM                     0          1        128          0          0          0          0          0          3          0                     0
   1 _SYSSMU1_3724004606$       1          3        128  340871758          3       2634        776          0          3          2                     2
   2 _SYSSMU2_2996391332$       1          3        144  340871760          3       2880       1144          0          3          2                     2
   3 _SYSSMU3_1723003836$       1          3        160  340871979          3       2921       1506          0          3          2                     2
   4 _SYSSMU4_1254879796$       1          3        176  340871764          3       2782       1273          0          3          2                     2
   5 _SYSSMU5_898567397$        1          3        192  340871766          3       3011       1147          0          3          2                     2
   6 _SYSSMU6_1263032392$       1          3        208  340872002          3       3268        897          0          3          2                     2
   7 _SYSSMU7_2070203016$       1          3        224  340871998          3       4937       1197          0          3          2                     2
   8 _SYSSMU8_517538920$        1          3        240  340871772          3       8287       1351          0          3          2                     2
   9 _SYSSMU9_1650507775$       1          3        256  340871992          3      11684       1097          0          3          2                     2
  10 _SYSSMU10_1197734989$      1          3        272  340872006          3      24725       4194          0          3          2                     2
  11 _SYSSMU11_1701842685$      1          3        248  337617109          3        557        362          0          2          2                     2
  12 _SYSSMU12_3785813942$      1          3        296  337514803          3       1747        624          0          2          2                     2
  13 _SYSSMU13_3860906822$      1          5        160     923661          0          2          1          0          1          5                     2
  14 _SYSSMU14_3319140121$      1          5        176     923323          0          2          1          0          1          5                     2
  15 _SYSSMU15_1436577151$      1          5        192     923332          0          2          1          0          1          5                     2
  16 _SYSSMU16_1689093467$      1          5        208     923314          0          2          1          0          1          5                     2
  17 _SYSSMU17_1049158485$      1          5        224     923296          0          2          1          0          1          5                     2
  18 _SYSSMU18_1557221903$      1          5        240     923320          0          2          1          0          1          5                     2
  19 _SYSSMU19_2284825117$      1          5        256     923294          0          2          1          0          1          5                     2
  20 _SYSSMU20_2312497597$      1          5        272     923262          0          2          1          0          1          5                     2
21 rows selected.

SYS@book> SELECT file#, CHECKPOINT_CHANGE#, CHECKPOINT_TIME,CREATION_CHANGE#  , RESETLOGS_CHANGE#,status, CHECKPOINT_COUNT,fuzzy,name,tablespace_name  FROM v$datafile_header;
FILE# CHECKPOINT_CHANGE# CHECKPOINT_TIME     CREATION_CHANGE# RESETLOGS_CHANGE# STATUS  CHECKPOINT_COUNT FUZ NAME                             TABLESPACE_NAME
----- ------------------ ------------------- ---------------- ----------------- ------- ---------------- --- -------------------------------- ----------------
    1        13225773903 2016-03-02 09:02:37                7            925702 ONLINE               744 YES /mnt/ramdisk/book/system01.dbf   SYSTEM
    2        13225773903 2016-03-02 09:02:37             1834            925702 ONLINE               744 YES /mnt/ramdisk/book/sysaux01.dbf   SYSAUX
    3        13225773903 2016-03-02 09:02:37           923328            925702 ONLINE               665 YES /mnt/ramdisk/book/undotbs01.dbf  UNDOTBS1
    4        13225773903 2016-03-02 09:02:37            16143            925702 ONLINE               744 YES /mnt/ramdisk/book/users01.dbf    USERS
    5        13225773903 2016-03-02 09:02:37           952916            925702 ONLINE               662 YES /mnt/ramdisk/book/example01.dbf  EXAMPLE
    6        13225773903 2016-03-02 09:02:37          1314508            925702 ONLINE               678 YES /mnt/ramdisk/book/sugar01.dbf    SUGAR
6 rows selected.

SYS@book> show parameter undo
NAME             TYPE     VALUE
---------------- -------- ----------
undo_management  string   AUTO
undo_retention   integer  900
undo_tablespace  string   UNDOTBS1

--很明显我个人不会在file#=5的数据文件上建立回滚段。实际上在8i dba要手工建立回滚段。8i下还有一个参数rollback_segments，这个参数在11g也存在

SYS@book> show parameter rollback_segments
NAME               TYPE     VALUE
------------------ -------- ---------------
rollback_segments  string

--当使用undo_management=manual 时，可以手工指定。但是当我查询：
SYS@book> select * from dba_extents where segment_name like '_SYSSMU%' and file_id=5 ;
no rows selected

--没有结果。

SYS@book> column SEGMENT_NAME format a30
SYS@book> select * from dba_extents where file_id=5 and block_id between 160 and 272+16 order by block_id;
OWNER  SEGMENT_NAME             SEGMENT_TYPE TABLESPACE_NAME EXTENT_ID      FILE_ID     BLOCK_ID        BYTES       BLOCKS RELATIVE_FNO
------ ------------------------ ------------ --------------- --------- ------------ ------------ ------------ ------------ ------------
HR     LOC_ID_PK                INDEX        EXAMPLE                 0            5          160        65536            8            5
HR     DEPARTMENTS              TABLE        EXAMPLE                 0            5          168        65536            8            5
HR     DEPT_ID_PK               INDEX        EXAMPLE                 0            5          176        65536            8            5
HR     JOBS                     TABLE        EXAMPLE                 0            5          184        65536            8            5
HR     JOB_ID_PK                INDEX        EXAMPLE                 0            5          192        65536            8            5
HR     EMPLOYEES                TABLE        EXAMPLE                 0            5          200        65536            8            5
HR     EMP_EMAIL_UK             INDEX        EXAMPLE                 0            5          208        65536            8            5
HR     EMP_EMP_ID_PK            INDEX        EXAMPLE                 0            5          216        65536            8            5
HR     JOB_HISTORY              TABLE        EXAMPLE                 0            5          224        65536            8            5
HR     JHIST_EMP_ID_ST_DATE_PK  INDEX        EXAMPLE                 0            5          232        65536            8            5
HR     EMP_DEPARTMENT_IX        INDEX        EXAMPLE                 0            5          240        65536            8            5
HR     EMP_JOB_IX               INDEX        EXAMPLE                 0            5          248        65536            8            5
HR     EMP_MANAGER_IX           INDEX        EXAMPLE                 0            5          256        65536            8            5
HR     EMP_NAME_IX              INDEX        EXAMPLE                 0            5          264        65536            8            5
HR     DEPT_LOCATION_IX         INDEX        EXAMPLE                 0            5          272        65536            8            5
HR     JHIST_JOB_IX             INDEX        EXAMPLE                 0            5          280        65536            8            5
HR     JHIST_EMPLOYEE_IX        INDEX        EXAMPLE                 0            5          288        65536            8            5
17 rows selected.

--很明显不是这些对象。拿那些回滚段从那里产生的呢？
--我安装的oracle测试数据库基本按照如下链接http://blog.itpub.net/267265/viewspace-1845062/。我当时做了一个冷备份。

--检查数据文件system01.dbf可以发现：
001C3460  00 00 00 2C 01 11 02 C1 08 14 5F 53 59 53 53 4D ...,......_SYSSM
001C3470  55 37 5F 32 30 37 30 32 30 33 30 31 36 24 02 C1 U7_2070203016$..
001C3480  02 02 C1 04 03 C2 03 19 04 C3 64 44 0E 01 80 03 ..........dD....
001C3490  C2 07 3D 03 C2 02 0C 01 80 02 C1 03 02 C1 03 FF ..=.............
001C34A0  FF FF FF 02 C1 03 2C 01 11 02 C1 0B 15 5F 53 59 ......,......_SY
001C34B0  53 53 4D 55 31 30 5F 31 31 39 37 37 33 34 39 38 SSMU10_119773498
001C34C0  39 24 02 C1 02 02 C1 04 03 C2 03 49 04 C3 64 46 9$.........I..dF
001C34D0  06 01 80 03 C2 09 30 03 C2 02 55 01 80 02 C1 03 ......0...U.....
001C34E0  02 C1 03 FF FF FF FF 02 C1 03 2C 00 11 02 C1 15 ..........,.....
001C34F0  15 5F 53 59 53 53 4D 55 32 30 5F 32 33 31 32 34 ._SYSSMU20_23124
001C3500  39 37 35 39 37 24 02 C1 02 02 C1 06 03 C2 03 49 97597$.........I
001C3510  04 C3 5D 21 3F 01 80 02 C1 03 02 C1 02 01 80 02 ..]!?...........
001C3520  C1 02 02 C1 06 FF FF FF FF 02 C1 03 2C 00 11 02 ............,...
001C3530  C1 14 15 5F 53 59 53 53 4D 55 31 39 5F 32 32 38 ..._SYSSMU19_228
001C3540  34 38 32 35 31 31 37 24 02 C1 02 02 C1 06 03 C2 4825117$........
001C3550  03 39 04 C3 5D 21 5F 01 80 02 C1 03 02 C1 02 01 .9..]!_.........
001C3560  80 02 C1 02 02 C1 06 FF FF FF FF 02 C1 03 2C 00 ..............,.
001C3570  11 02 C1 13 15 5F 53 59 53 53 4D 55 31 38 5F 31 ....._SYSSMU18_1
001C3580  35 35 37 32 32 31 39 30 33 24 02 C1 02 02 C1 06 557221903$......
001C3590  03 C2 03 29 04 C3 5D 22 15 01 80 02 C1 03 02 C1 ...)..]"........
001C35A0  02 01 80 02 C1 02 02 C1 06 FF FF FF FF 02 C1 03 ................
001C35B0  2C 00 11 02 C1 12 15 5F 53 59 53 53 4D 55 31 37 ,......_SYSSMU17
001C35C0  5F 31 30 34 39 31 35 38 34 38 35 24 02 C1 02 02 _1049158485$....
001C35D0  C1 06 03 C2 03 19 04 C3 5D 21 61 01 80 02 C1 03 ........]!a.....
001C35E0  02 C1 02 01 80 02 C1 02 02 C1 06 FF FF FF FF 02 ................
001C35F0  C1 03 2C 00 11 02 C1 11 15 5F 53 59 53 53 4D 55 ..,......_SYSSMU
001C3600  31 36 5F 31 36 38 39 30 39 33 34 36 37 24 02 C1 16_1689093467$..
001C3610  02 02 C1 06 03 C2 03 09 04 C3 5D 22 0F 01 80 02 ..........]"....
001C3620  C1 03 02 C1 02 01 80 02 C1 02 02 C1 06 FF FF FF ................
001C3630  FF 02 C1 03 2C 00 11 02 C1 10 15 5F 53 59 53 53 ....,......_SYSS
001C3640  4D 55 31 35 5F 31 34 33 36 35 37 37 31 35 31 24 MU15_1436577151$
001C3650  02 C1 02 02 C1 06 03 C2 02 5D 04 C3 5D 22 21 01 .........]..]"!.
001C3660  80 02 C1 03 02 C1 02 01 80 02 C1 02 02 C1 06 FF ................
001C3670  FF FF FF 02 C1 03 2C 00 11 02 C1 0F 15 5F 53 59 ......,......_SY
001C3680  53 53 4D 55 31 34 5F 33 33 31 39 31 34 30 31 32 SSMU14_331914012
001C3690  31 24 02 C1 02 02 C1 06 03 C2 02 4D 04 C3 5D 22 1$.........M..]"
001C36A0  18 01 80 02 C1 03 02 C1 02 01 80 02 C1 02 02 C1 ................
001C36B0  06 FF FF FF FF 02 C1 03 2C 00 11 02 C1 0E 15 5F ........,......_
001C36C0  53 59 53 53 4D 55 31 33 5F 33 38 36 30 39 30 36 SYSSMU13_3860906

--这些回滚段_SYSSMU20_2312497597$在undo中已经存在，我那种安装相当于copy过来的，估计以前曾经有数据文件5做过undo表空间。
--不知道为什么没有清除，目前不影响测试，先暂时不管它。