[20181123]模擬ora-01555.txt

--//ora-01555一般情況是回滾找不到前映像(已經被覆蓋),報這個錯誤。透過bbed修改塊模擬看看。

$ oerr ora 1555

01555, 00000, "snapshot too old: rollback segment number %s with name \"%s\" too small"

// *Cause: rollback records needed by a reader for consistent read are

// overwritten by other writers

// *Action: If in Automatic Undo Management mode, increase undo_retention

// setting. Otherwise, use larger rollback segments

1.環境：

SCOTT@book> @ 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

SCOTT@book> select current_scn from v$database;

CURRENT_SCN

------------

13276934327

SCOTT@book> @ tx 13276934327 32

select 13276934327,trunc(13276934327/power(2,32)) scn_wrap,mod(13276934327,power(2,32)) scn_base from dual

13276934327 SCN_WRAP SCN_BASE SCN_WRAP16 SCN_BASE16

------------ ------------ ------------ ---------- ----------

13276934327 3 392032439 3 175df0b7

--//SCN_WRAP=3.

SCOTT@book> create table t as select rownum id ,'test' name from dual connect by level<=2;

Table created.

SCOTT@book> select rowid,t.* from t;

ROWID ID NAME

------------------ ------------ -----

AAAWEGAAEAAAAIjAAA 1 test

AAAWEGAAEAAAAIjAAB 2 test

SCOTT@book> @ rowid AAAWEGAAEAAAAIjAAA

OBJECT FILE BLOCK ROW ROWID_DBA DBA TEXT

------------ ------------ ------------ ------------ -------------------- -------------------- ----------------------------------------

90374 4 547 0 0x1000223 4,547 alter system dump datafile 4 block 547 ;

SCOTT@book> delete from t where id=1;

1 row deleted.

SCOTT@book> commit ;

Commit complete.

SCOTT@book> alter system checkpoint ;

System altered.

SCOTT@book> alter system flush buffer_cache;

System altered.

2.bbed修改塊產生ora-01555錯誤。

BBED> set dba 4,547

DBA 0x01000223 (16777763 4,547)

BBED> x /rnc *kdbr[0]

rowdata[11] @8177

-----------

flag@8177: 0x3c (KDRHFL, KDRHFF, KDRHFD, KDRHFH)

lock@8178: 0x02

cols@8179: 0

--//使用事務槽2.從0開始編號.

BBED> x /rnc *kdbr[1]

rowdata[0] @8166

----------

flag@8166: 0x2c (KDRHFL, KDRHFF, KDRHFH)

lock@8167: 0x00

cols@8168: 2

col 0[2] @8169: 2

col 1[4] @8172: test

BBED> p ktbbh.ktbbhitl[1]

struct ktbbhitl[1], 24 bytes @68

struct ktbitxid, 8 bytes @68

ub2 kxidusn @68 0x000a

ub2 kxidslt @70 0x0011

ub4 kxidsqn @72 0x00004bea

struct ktbituba, 8 bytes @76

ub4 kubadba @76 0x00c0104d

ub2 kubaseq @80 0x0eb5

ub1 kubarec @82 0x24

ub2 ktbitflg @84 0x2001 (KTBFUPB)

union _ktbitun, 2 bytes @86

sb2 _ktbitfsc @86 9

ub2 _ktbitwrp @86 0x0009

ub4 ktbitbas @88 0x175df15e

--//ktbbh.ktbbhitl[1]._ktbitun._ktbitfsc表示dml操作回事的空間(不包括flag,lock),1+1+2+1+4 = 9.

--//當itl槽重用時,這數值加入kdbh.kdbhavsp.

--//修改ktbbh.ktbbhitl[1].ktbitbas=0x275df15e

BBED> assign ktbbh.ktbbhitl[1].ktbitbas=0x275df15e

Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y

ub4 ktbitbas @88 0x275df15e

BBED> sum apply ;

Check value for File 4, Block 547:

current = 0x051d, required = 0x051d

--//注:按照道理itl事務槽的提交scn號不應該大於塊號的scn號,因為它不包括wrap部分,oracle一般不會認為錯誤.

--//另外我設定_ktbitwrp=4.修改ktbitflg=0x8000,也不報錯.

--//開啟新會話可以發現可以透過回滾段查詢資料.依舊可以查詢到刪除資料.

SCOTT@book> select * from t;

ID NAME

---------- --------------------

1 test

2 test

3.遮蔽回滾段看看.

SCOTT@book> select * from v$rollname where usn=10;

USN NAME

---------- ----------------------

10 _SYSSMU10_1197734989$

SYS@book> create pfile='/tmp/@.ora' from spfile;

File created.

--//修改/tmp/book.ora加入如下:

*._corrupted_rollback_segments='_SYSSMU10_1197734989$'

SYS@book> shutdown immediate ;

Database closed.

Database dismounted.

ORACLE instance shut down.

SYS@book> startup pfile='/tmp/book.ora';

ORACLE instance started.

Total System Global Area 643084288 bytes

Fixed Size 2255872 bytes

Variable Size 205521920 bytes

Database Buffers 427819008 bytes

Redo Buffers 7487488 bytes

Database mounted.

Database opened.

SYS@book> set numw 12

SYS@book> select current_scn from v$database ;

CURRENT_SCN

------------

13276936029

SYS@book> @ tx 13276936029 32

select 13276936029,trunc(13276936029/power(2,32)) scn_wrap,mod(13276936029,power(2,32)) scn_base from dual

13276936029 SCN_WRAP SCN_BASE SCN_WRAP16 SCN_BASE16

------------ ------------ ------------ ---------- ----------

13276936029 3 392034141 3 175df75d

SYS@book> select * from scott.t;

select * from scott.t

*

ERROR at line 1:

ORA-01555: snapshot too old: rollback segment number with name "" too small

--//因為設定了*._corrupted_rollback_segments='_SYSSMU10_1197734989$'.看不到回滾段號.

4.順便溫習提升scn:

SYS@book> shutdown immediate ;

Database closed.

Database dismounted.

ORACLE instance shut down.

SYS@book> startup mount pfile='/tmp/book.ora';

ORACLE instance started.

Total System Global Area 643084288 bytes

Fixed Size 2255872 bytes

Variable Size 205521920 bytes

Database Buffers 427819008 bytes

Redo Buffers 7487488 bytes

Database mounted.

SYS@book> oradebug setmypid

Statement processed.

SYS@book> oradebug DUMPvar SGA kcsgscn_

kcslf kcsgscn_ [06001AE70, 06001AEA0) = 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000

--//僅僅到mount狀態,scn沒有載入,看到是0.

SYS@book> oradebug poke 0x06001AE70 4 0x375df75d

BEFORE: [06001AE70, 06001AE74) = 00000000

AFTER: [06001AE70, 06001AE74) = 375DF75D

--//注意還沒有完,必須修改scn_wrap部分.

SYS@book> oradebug poke 0x06001AE74 4 0x00000003

BEFORE: [06001AE74, 06001AE78) = 00000000

AFTER: [06001AE74, 06001AE78) = 00000003

SYS@book> oradebug DUMPvar SGA kcsgscn_

kcslf kcsgscn_ [06001AE70, 06001AEA0) = 375DF75D 00000003 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000

--//注意千萬不要一次修改完成,這樣實際上錯誤的.我測試犯了嚴重錯誤!!

SYS@book> oradebug poke 0x06001AE70 8 0x375df75d00000003

BEFORE: [06001AE70, 06001AE78) = 375DF75D 00000003

AFTER: [06001AE70, 06001AE78) = 00000003 375DF75D

SYS@book> oradebug DUMPvar SGA kcsgscn_

kcslf kcsgscn_ [06001AE70, 06001AEA0) = 00000003 375DF75D 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000

--//實際上這樣scn_wrap變成了0xF75D,scn_base=0x00000003.這樣scn提升太快了,會出現如下錯誤ora-00600[2552]:

ARC1 started with pid=23, OS id=53718

Errors in file /u01/app/oracle/diag/rdbms/book/book/trace/book_lgwr_53688.trc (incident=2271885):

ORA-00600: internal error code, arguments: [2252], [5318], [4], [3787], [3340107776], [], [], [], [], [], [], []

Incident details in: /u01/app/oracle/diag/rdbms/book/book/incident/incdir_2271885/book_lgwr_53688_i2271885.trc

Use ADRCI or Support Workbench to package the incident.

See Note 411.1 at My Oracle Support for error and packaging details.

Errors in file /u01/app/oracle/diag/rdbms/book/book/trace/book_lgwr_53688.trc:

ORA-00600: internal error code, arguments: [2252], [5318], [4], [3787], [3340107776], [], [], [], [], [], [], []

LGWR (ospid: 53688): terminating the instance due to error 470

Fri Nov 23 09:33:13 2018

System state dump requested by (instance=1, osid=53688 (LGWR)), summary=[abnormal instance termination].

System State dumped to trace file /u01/app/oracle/diag/rdbms/book/book/trace/book_diag_53674_20181123093313.trc

Dumping diagnostic data in directory=[cdmp_20181123093313], requested by (instance=1, osid=53688 (LGWR)), summary=[abnormal instance termination].

Instance terminated by LGWR, pid = 53688

----------------

--//還原:

SYS@book> oradebug poke 0x06001AE70 4 0x375df75d

BEFORE: [06001AE70, 06001AE74) = 00000003

AFTER: [06001AE70, 06001AE74) = 375DF75D

SYS@book> oradebug poke 0x06001AE74 4 0x00000003

BEFORE: [06001AE74, 06001AE78) = 375DF75D

AFTER: [06001AE74, 06001AE78) = 00000003

SYS@book> oradebug DUMPvar SGA kcsgscn_

kcslf kcsgscn_ [06001AE70, 06001AEA0) = 375DF75D 00000003 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 6001AB50 00000000

--//這樣scn號提升到 0x3375DF75D=13813806941.

SYS@book> alter database open ;

Database altered.

SYS@book> select * from scott.t;

ID NAME

---------- --------------------

2 test

--//OK,現在看不到id=1的記錄.

SYS@book> select current_scn from v$database ;

CURRENT_SCN

------------

13813807246

[20181123]模擬ora-01555.txt

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