[20191206]隐含参数_db_always_check_system_ts.txt

[20191206]隐含参数_db_always_check_system_ts.txt --//今年年头我做tab$删除恢复时,遇到的问题,就是遇到延迟块清除的问题.参考链接: http://blog.itpub.net/267265/viewspace-2564716/ http://blog.itpub.net/267265/viewspace-2564717/ --//当时测试如果发生延迟块清除,修复删除记录的块,再读取时如果是系统表空间时报错,一般用户的表空间是没有问题. --//一直想知道系统表空间有什么隐含参数可以绕过这个问题,毕竟修复数据库如果错误太多,无法一块一块来修复. --//昨天才知道有一个隐含参数_db_always_check_system_ts可以绕过这个错误.今天测试看看. 1.环境: 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 SYS@book> @ hide _db_always_check_system_ts NAME                       DESCRIPTION                                                   DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE ISSES ISSYS_MOD -------------------------- ------------------------------------------------------------- ------------- ------------- ------------ ----- --------- _db_always_check_system_ts Always perform block check and checksum for System tablespace TRUE          TRUE          TRUE         FALSE IMMEDIATE --//缺省_db_always_check_system_ts=true. 2.测试: SYS@book> create table t tablespace system as select rownum id,'test' name from dual connect by level<=2; Table created. SYS@book> select rowid,t.* from t; ROWID                      ID NAME ------------------ ---------- ---- AAAWEgAABAAAAl5AAA          1 test AAAWEgAABAAAAl5AAB          2 test SYS@book> @ rowid AAAWEgAABAAAAl5AAA     OBJECT       FILE      BLOCK        ROW ROWID_DBA            DBA                  TEXT ---------- ---------- ---------- ---------- -------------------- -------------------- ----------------------------------------      90400          1       2425          0   0x400979           1,2425               alter system dump datafile 1 block 2425 -//建立在system表空间. SYS@book>  delete from t where id=1; 1 row deleted. SYS@book>  alter system flush buffer_cache; System altered. SYS@book>  alter system flush buffer_cache; System altered. SYS@book> @ bh 1 2425 HLADDR              DBARFIL     DBABLK      CLASS CLASS_TYPE         STATE             TCH CR_SCN_BAS CR_SCN_WRP CR_UBA_FIL CR_UBA_BLK CR_UBA_SEQ BA               OBJECT_NAME ---------------- ---------- ---------- ---------- ------------------ ---------- ---------- ---------- ---------- ---------- ---------- ---------- ---------------- -------------------- 0000000084DEACF8          1       2425          1 data block         free                0          0          0          0          0          0 00000000772C2000 T 0000000084DEACF8          1       2425          1 data block         free                0          0          0          0          0          0 00000000772C4000 T --//确定该块不在数据库缓存. SYS@book> commit ; Commit complete. --//这个时候不会写块提交到块中,因为数据块已经不在数据缓存了. 3.使用bbed修复该记录看看: BBED> set dba   1,2425         DBA             0x00400979 (4196729 1,2425) 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> x /rnc *kdbr[0] rowdata[11]                                 @8177 ----------- flag@8177: 0x3c (KDRHFL, KDRHFF, KDRHFD, KDRHFH) lock@8178: 0x02 cols@8179:    0 --//第1条记录已经删除,flag=0x3c. BBED> assign offset 8177 =0x2c; Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y ub1 rowdata[0]                              @8177     0x2c BBED> x /rnc *kdbr[0] rowdata[11]                                 @8177 ----------- flag@8177: 0x2c (KDRHFL, KDRHFF, KDRHFH) lock@8178: 0x02 cols@8179:    2 col    0[2] @8180: 1 col    1[4] @8183: test --//ok,现在已经恢复.lock=0x02,使用itl槽1(从0开始) BBED> sum apply Check value for File 1, Block 2425: current = 0xff20, required = 0xff20 BBED> verify DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 Block Checking: DBA = 4196729, Block Type = KTB-managed data block data header at 0x7f344dbba274 kdbchk: the amount of space used is not equal to block size         used=44 fsc=9 avsp=8028 dtl=8072 Block 2425 failed with check code 6110 --//注:这个报错不必理会在select读取时. BBED> p ktbbh.ktbbhitl[1] struct ktbbhitl[1], 24 bytes                @68    struct ktbitxid, 8 bytes                 @68       ub2 kxidusn                           @68       0x000a       ub2 kxidslt                           @70       0x0013       ub4 kxidsqn                           @72       0x00004d92    struct ktbituba, 8 bytes                 @76       ub4 kubadba                           @76       0x00c00288       ub2 kubaseq                           @80       0x0f0a       ub1 kubarec                           @82       0x0e    ub2 ktbitflg                             @84       0x0002 (NONE)    union _ktbitun, 2 bytes                  @86       sb2 _ktbitfsc                         @86       9       ub2 _ktbitwrp                         @86       0x0009    ub4 ktbitbas                             @88       0x00000000 --//可以发现ktbitflg=0x0002,表示没有提交.有点奇怪为什么是0x0002,应该是0x0001(因为我仅仅删除1条记录) --//注:关于这点我在以前blog提到参考链接http://blog.itpub.net/267265/viewspace-2564779/,视乎使用表空间类型是mssm就能看到 --//这样的情况. --//ktbitbas=0x00000000,也就是没有scn相关信息写入. --//如果我这时读取该块就会遇到链接测试遇到的情况:链接http://blog.itpub.net/267265/viewspace-2564717/ ORA-00607: Internal error occurred while making a change to a data block ORA-00600: internal error code, arguments: [kdBlkCheckError], [1], [2537], [6110], [], [], [], [], [], [], [], [] --//注意错误号6110,与bbed的错误号一致. --//因为延迟块清除,在读取该块时要写入itl槽scn号.设置提交标识.这样对于system表空间这样的块就会报错(bbed verify没有通过) --//现在修改参数: SYS@book> alter system set "_db_always_check_system_ts"=false scope=memory ; System altered. SYS@book> @ hide "_db_always_check_system_ts" NAME                       DESCRIPTION                                                   DEFAULT_VALUE SESSION_VALUE SYSTEM_VALUE ISSES ISSYS_MOD -------------------------- ------------------------------------------------------------- ------------- ------------- ------------ ----- --------- _db_always_check_system_ts Always perform block check and checksum for System tablespace TRUE          FALSE         FALSE        FALSE IMMEDIATE --//按照介绍该参数是立即生效ISSYS_MOD=IMMEDIATE.保险起见还是退出会话在登录看看. SYS@book> select rowid,t.* from t; ROWID               ID NAME ------------------ --- ----- AAAWEgAABAAAAl5AAA   1 test AAAWEgAABAAAAl5AAB   2 test --//OK,现在读取就没有问题.再次通过bbed观察: BBED> set dba   1,2425         DBA             0x00400979 (4196729 1,2425) BBED> p ktbbh.ktbbhitl[1] struct ktbbhitl[1], 24 bytes                @68    struct ktbitxid, 8 bytes                 @68       ub2 kxidusn                           @68       0x000a       ub2 kxidslt                           @70       0x0013       ub4 kxidsqn                           @72       0x00004d92    struct ktbituba, 8 bytes                 @76       ub4 kubadba                           @76       0x00c00288       ub2 kubaseq                           @80       0x0f0a       ub1 kubarec                           @82       0x0e    ub2 ktbitflg                             @84       0xa000 (KTBFUPB, KTBFCOM)`    union _ktbitun, 2 bytes                  @86       sb2 _ktbitfsc                         @86       3       ub2 _ktbitwrp                         @86       0x0003    ub4 ktbitbas                             @88       0x17600426 --//可以发现ktbitflg=0xa000(KTBFUPB, KTBFCOM),表示提交. --//ktbitbas=0x17600426,也就是scn相关信息已经写入. BBED> verify DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 Block Checking: DBA = 4196729, Block Type = KTB-managed data block data header at 0x1f09e74 kdbchk: the amount of space used is not equal to block size         used=44 fsc=0 avsp=8037 dtl=8072 Block 2425 failed with check code 6110 --//还是报6110错误.但是该块的读取是没有问题的. SYS@book> alter system set "_db_always_check_system_ts"=true scope=memory ; System altered. SYS@book> select rowid,t.* from t; ROWID                      ID NAME ------------------ ---------- ---- AAAWEgAABAAAAl5AAA          1 test AAAWEgAABAAAAl5AAB          2 test --//读取没有问题,如果修改该记录现在就会报错(注意"_db_always_check_system_ts"=true),验证看看. SYS@book> update t set name='TEST' where id=2; update t set name='TEST' where id=2        * ERROR at line 1: ORA-00600: internal error code, arguments: [kdBlkCheckError], [1], [2425], [6110], [], [], [], [], [], [], [], [] SYS@book> alter system set "_db_always_check_system_ts"=false scope=memory ; System altered. SYS@book> update t set name='TEST' where id=2; update t set name='TEST' where id=2        * ERROR at line 1: ORA-01578: ORACLE data block corrupted (file # 1, block # 2425) ORA-01110: data file 1: '/mnt/ramdisk/book/system01.dbf' SYS@book> alter system flush buffer_cache; System altered. SYS@book> update t set name='TEST' where id=2; 1 row updated. --//ok现在没有问题. SYS@book> commit ; Commit complete. SYS@book> select rowid,t.* from t; ROWID               ID NAME ------------------ --- ----- AAAWEgAABAAAAl5AAA   1 test AAAWEgAABAAAAl5AAB   2 TEST --//实际上这个时候使用bbed verify检查还是报错. BBED> set dba   1,2425         DBA             0x00400979 (4196729 1,2425) BBED> verify DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 Block Checking: DBA = 4196729, Block Type = KTB-managed data block data header at 0x7f756ceee274 kdbchk: the amount of space used is not equal to block size         used=44 fsc=0 avsp=8037 dtl=8072 Block 2425 failed with check code 6110 4.总结: --//设置_db_always_check_system_ts=false,可以绕过一些数据库块错误,实际上遇到这样的情况,最佳的方式设置read only. --//采用exp或者expdp方式尽快取出数据重新建库. 5.补充如何修复该块: BBED> verify dba 1,2425 DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 Block Checking: DBA = 4196729, Block Type = KTB-managed data block data header at 0x15b9e74 kdbchk: the amount of space used is not equal to block size         used=44 fsc=0 avsp=8037 dtl=8072 Block 2425 failed with check code 6110 --//avsp= dtl-used-fsc = 8072-0 -44 = 8028 BBED> assign kdbh.kdbhavsp=8028 Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y sb2 kdbhavsp                                @126      8116 BBED> assign kdbh.kdbhavsp=8028 sb2 kdbhavsp                                @126      8028 BBED> sum apply Check value for File 1, Block 2425: current = 0x8014, required = 0x8014 BBED> verify dba 1,2425 DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 Block Checking: DBA = 4196729, Block Type = KTB-managed data block data header at 0x16d5e74 kdbchk: space available on commit is incorrect         tosp=8039 fsc=0 stb=0 avsp=8028 Block 2425 failed with check code 6111 --// tosp = avsp+stb+fsc= 8028+0+0 = 8028 BBED> assign kdbh.kdbhtosp=8028 sb2 kdbhtosp                                @128      8028 BBED> sum apply Check value for File 1, Block 2425: current = 0x802f, required = 0x802f BBED> verify dba 1,2425 DBVERIFY - Verification starting FILE = /mnt/ramdisk/book/system01.dbf BLOCK = 2425 --//现在设置"_db_always_check_system_ts"=true,在执行dml就不错报错了. SYS@book> alter system set "_db_always_check_system_ts"=true scope=memory ; System altered. SYS@book> update t set name='Tttt' where id=2; 1 row updated. SYS@book> commit ; Commit complete. SYS@book> select rowid,t.* from t; ROWID                      ID NAME ------------------ ---------- ---- AAAWEgAABAAAAl5AAA          1 test AAAWEgAABAAAAl5AAB          2 Tttt