db_block_checksum实质是通过flg_kcbh来控制block checksum

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标题：db_block_checksum实质是通过flg_kcbh来控制block checksum

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

db_block_checksum 用于DBWn和direct loader数据块写入到磁盘时，基于块内的所有字节计算得出一个校验值并将其写入块头。在该参数设置为typical和full时，当读入时候重新计算校验和写出时候的校验对比，如果不同则认为是块损坏。如果设置为FULL模式,则基于update/delete应用程序语句级别的改变发生后，校验值会被重新计算并写入。同时对于日志块，在写入之前，同样会生产校验值并写入到块头。该参数主要是防止IO硬件和IO子系统的错误。
这里提示我们是在系统参数级别使用db_block_checksum来控制block是否进行验证，那在block本身级别，是否有类似的值来控制，实现对block值的checksum？通过dump结合bbed给出相关答案
db_block_checksum为TYPICAL测试

CDB_CDB$ROOT@SYS> show parameter db_block_checksum;
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_block_checksum                    string      TYPICAL
CDB_CDB$ROOT@SYS> conn / as sysdba
已连接。
CDB_CDB$ROOT@SYS> alter session set container=pdb;
会话已更改。
CDB_CDB$ROOT@SYS> alter database open;
数据库已更改。
CDB_CDB$ROOT@SYS> alter session set current_schema=chf;
会话已更改。
CDB_CDB$ROOT@SYS> create table t_xifenfei(id number,name varchar2(100));
表已创建。
CDB_CDB$ROOT@SYS> insert into t_xifenfei values(1,'www.xifenfei.com');
已创建 1 行。
CDB_CDB$ROOT@SYS> alter system checkpoint;
系统已更改。
CDB_CDB$ROOT@SYS>  select dbms_rowid.rowid_relative_fno(rowid) file_no,
2  dbms_rowid.rowid_block_number(rowid) block_no  from t_xifenfei;
   FILE_NO   BLOCK_NO
---------- ----------
         9      19229
CDB_CDB$ROOT@SYS> SELECT NAME FROM V$DATAFILE WHERE FILE#=9;
NAME
---------------------------------------------------------------------
E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF

dump 该block

buffer tsn: 3 rdba: 0x02404b1d (9/19229)
scn: 0xb8c.3c232935 seq: 0x01 flg: 0x06 tail: 0x29350601
frmt: 0x02 chkval: 0xe08b type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
tab 0, row 0, @0x1f81
tl: 23 fb: --H-FL-- lb: 0x1  cc: 2
col  0: [ 2]  c1 02
col  1: [16]  77 77 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
end_of_block_dump
End dump data blocks tsn: 3 file#: 9 minblk 19229 maxblk 19229

这里可以看到因为db_block_checksum=TYPICAL，因此插入记录的时候，dump block发现flg: 0x06 和 chkval: 0xe08b

使用bbed查看相关记录
补充:在win系统中,bbed查看block和block num相差1

BBED> p kcbh
struct kcbh, 20 bytes                       @0
   ub1 type_kcbh                            @0        0x06
   ub1 frmt_kcbh                            @1        0xa2
   ub1 spare1_kcbh                          @2        0x00
   ub1 spare2_kcbh                          @3        0x00
   ub4 rdba_kcbh                            @4        0x02404b1d
   ub4 bas_kcbh                             @8        0x3c232935
   ub2 wrp_kcbh                             @12       0x0b8c
   ub1 seq_kcbh                             @14       0x01
   ub1 flg_kcbh                             @15       0x06 (KCBHFDLC, KCBHFCKV)
   ub2 chkval_kcbh                          @16       0xe08b
   ub2 spare3_kcbh                          @18       0x0000

通过对比bbed和dump出来数据，可以得出flg: 0x06(flg_kcbh),chkval: 0xe08b(chkval_kcbh)

使用bbed修改block验证chkval_kcbh
提问：在使用bbed修改block的时候，一般都需要使用sum apply 处理下，为什么呢？

BBED> d /v
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19230   Offsets: 8165 to 8191  Dba:0x00000000
-------------------------------------------------------
 2c010202 c1021077 77772e78 6966656e l ,...?.www.xifen
 6665692e 636f6d01 063529            l fei.com..5)
 <16 bytes per line>
--没有修改任何值，sum的current和required值相同，而且和chkval_kcbh也相同
BBED> sum
Check value for File 0, Block 19230:
current = 0xe08b, required = 0xe08b
--尝试修改值
BBED> m /x 78 offset 8173
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19230            Offsets: 8173 to 8191           Dba:0x00000000
------------------------------------------------------------------------
 78772e78 6966656e 6665692e 636f6d01 063529
 <32 bytes per line>
BBED> d /v offset 8165
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19230   Offsets: 8165 to 8191  Dba:0x00000000
-------------------------------------------------------
 2c010202 c1021077 78772e78 6966656e l ,...?.wxw.xifen
 6665692e 636f6d01 063529            l fei.com..5)
 <16 bytes per line>
--发现current<>required
BBED> sum
Check value for File 0, Block 19230:
current = 0xe08b, required = 0xef8b
--apply把current修改为required值
BBED> sum apply
Check value for File 0, Block 19230:
current = 0xef8b, required = 0xef8b
--发现chkval_kcbh也修改为了required值
BBED> p kcbh.chkval_kcbh
ub2 chkval_kcbh                             @16       0xef8b

通过这里可以发现，在flg_kcbh含(KCBHFCKV)的情况下，如果block发生改变，则运行sum apply之后chkval_kcbh也发生改变

继续dump block

buffer tsn: 3 rdba: 0x02404b1d (9/19229)
scn: 0xb8c.3c232935 seq: 0x01 flg: 0x06 tail: 0x29350601
frmt: 0x02 chkval: 0xef8b type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
tab 0, row 0, @0x1f81
tl: 23 fb: --H-FL-- lb: 0x1  cc: 2
col  0: [ 2]  c1 02
col  1: [16]  77 78 77 2e 78 69 66 65 6e 66 65 69 2e 63 6f 6d
end_of_block_dump
End dump data blocks tsn: 3 file#: 9 minblk 19229 maxblk 19229

证明上述结论正确:dump.flg=bbed.flg_kcbh，dump.chkval=bbed.chkval_kcbh

db_block_checksum为FALSE测试

CDB_CDB$ROOT@SYS> alter system set db_block_checksum=false;
系统已更改。
CDB_CDB$ROOT@SYS> drop table t_xifenfei_new purge;
表已删除。
CDB_CDB$ROOT@SYS> alter session set current_schema=chf;
会话已更改。
CDB_CDB$ROOT@SYS>  create table t_xifenfei_new(id number,name varchar2(100));
表已创建。
CDB_CDB$ROOT@SYS>  insert into t_xifenfei_new values(1,'www.orasos.com');
已创建 1 行。
CDB_CDB$ROOT@SYS> commit;
提交完成。
CDB_CDB$ROOT@SYS>  select dbms_rowid.rowid_relative_fno(rowid) file_no,
 2  dbms_rowid.rowid_block_number(rowid) block_no  from t_xifenfei_new;
   FILE_NO   BLOCK_NO
---------- ----------
         9      19237
CDB_CDB$ROOT@SYS> alter system checkpoint;
系统已更改。
CDB_CDB$ROOT@SYS> alter system dump datafile 9 block 19237;
系统已更改。

dump block分析

buffer tsn: 3 rdba: 0x02404b25 (9/19237)
scn: 0xb8c.3c23c8b2 seq: 0x01 flg: 0x02 tail: 0xc8b20601
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
tab 0, row 0, @0x1f83
tl: 21 fb: --H-FL-- lb: 0x1  cc: 2
col  0: [ 2]  c1 02
col  1: [14]  77 77 77 2e 6f 72 61 73 6f 73 2e 63 6f 6d
end_of_block_dump
End dump data blocks tsn: 3 file#: 9 minblk 19237 maxblk 19237

这里可以发现当设置db_block_checksum=false之时，插入数据,显示flg: 0x02，chkval: 0x0000，由此猜测无对block写入进行部分验证(tailchk依然验证)

使用bbed修改block

BBED> set filename 'E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF'
        FILENAME        E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF
BBED> set blocksize 19238
BBED-00108: illegal BLOCKSIZE (19238) specified
BBED> set blocksize 8192
        BLOCKSIZE       8192
BBED> set block 8192
        BLOCK#          8192
BBED> set blocksize 19238
BBED-00108: illegal BLOCKSIZE (19238) specified
BBED> set block 19238
        BLOCK#          19238
BBED> p kcbh
struct kcbh, 20 bytes                       @0
   ub1 type_kcbh                            @0        0x06
   ub1 frmt_kcbh                            @1        0xa2
   ub1 spare1_kcbh                          @2        0x00
   ub1 spare2_kcbh                          @3        0x00
   ub4 rdba_kcbh                            @4        0x02404b25
   ub4 bas_kcbh                             @8        0x3c23c8b2
   ub2 wrp_kcbh                             @12       0x0b8c
   ub1 seq_kcbh                             @14       0x01
   ub1 flg_kcbh                             @15       0x02 (KCBHFDLC)
   ub2 chkval_kcbh                          @16       0x0000
   ub2 spare3_kcbh                          @18       0x0000
--这里看到flg_kcbh与chkval_kcbh和dump结果一致
BBED> sum
Check value for File 0, Block 19238:
current = 0x0000, required = 0x0000
--required为0，表示不验证
BBED> d /v offset 8174
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238   Offsets: 8174 to 8191  Dba:0x00000000
-------------------------------------------------------
 7777772e 6f726173 6f732e63 6f6d0106 l www.orasos.com..
 b2c8                                l 踩
 <16 bytes per line>
BBED> set mode edit
        MODE            Edit
BBED> m /x 78
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 8174 to 8191           Dba:0x00000000
------------------------------------------------------------------------
 7877772e 6f726173 6f732e63 6f6d0106 b2c8
 <32 bytes per line>
BBED> d /v
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238   Offsets: 8174 to 8191  Dba:0x00000000
-------------------------------------------------------
 7877772e 6f726173 6f732e63 6f6d0106 l xww.orasos.com..
 b2c8                                l 踩
 <16 bytes per line>
--修改了block，但是sum依然提示required为0
BBED> sum
Check value for File 0, Block 19238:
current = 0x0000, required = 0x0000
BBED> sum apply
Check value for File 0, Block 19238:
current = 0x0000, required = 0x0000

dump block核对

buffer tsn: 3 rdba: 0x02404b25 (9/19237)
scn: 0xb8c.3c23c8b2 seq: 0x01 flg: 0x02 tail: 0xc8b20601
frmt: 0x02 chkval: 0x0000 type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
tab 0, row 0, @0x1f83
tl: 21 fb: --H-FL-- lb: 0x1  cc: 2
col  0: [ 2]  c1 02
col  1: [14]  78 77 77 2e 6f 72 61 73 6f 73 2e 63 6f 6d
end_of_block_dump
End dump data blocks tsn: 3 file#: 9 minblk 19237 maxblk 19237

修改flg_kcbh测试

BBED> m /x 06 offset 15
Warning: contents of previous BIFILE will be lost. Proceed? (Y/N) y
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets:   15 to   30           Dba:0x00000000
------------------------------------------------------------------------
 06000000 00010000 00d86b01 00aec823
 <32 bytes per line>
BBED> sum
Check value for File 0, Block 19238:
current = 0x0000, required = 0x04b3
--修改flg_kcbh=x06后，sum中的required出现了非0值，表示已经启动了block完整性检测
BBED> m /x 79 offset 1876
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 1876 to 1891           Dba:0x00000000
------------------------------------------------------------------------
 79391b01 0000c24e 07000205 c406573f
 <32 bytes per line>
BBED> sum
Check value for File 0, Block 19238:
current = 0x0000, required = 0x049d
--修改了chkval_kcbh值
BBED> sum apply
Check value for File 0, Block 19238:
current = 0x049d, required = 0x049d

再次检查dump block

buffer tsn: 3 rdba: 0x02404b25 (9/19237)
scn: 0xb8c.3c23c8b2 seq: 0x01 flg: 0x06 tail: 0xc8b20601
frmt: 0x02 chkval: 0x049d type: 0x06=trans data
Hex dump of block: st=0, typ_found=1
tl: 21 fb: --H-FL-- lb: 0x1  cc: 2
col  0: [ 2]  c1 02
col  1: [14]  78 77 77 2e 6f 72 61 73 6f 73 2e 63 6f 6d
end_of_block_dump
End dump data blocks tsn: 3 file#: 9 minblk 19237 maxblk 19237

证明修改flg_kcbh后，block的sum验证起效

完整测试

--flg_kcbh=2,chkval_kcbh为04b3，修改block观察变化
BBED> sum
Check value for File 0, Block 19238:
current = 0x04b3, required = 0x04b3
BBED> p kcbh
struct kcbh, 20 bytes                       @0
   ub1 type_kcbh                            @0        0x06
   ub1 frmt_kcbh                            @1        0xa2
   ub1 spare1_kcbh                          @2        0x00
   ub1 spare2_kcbh                          @3        0x00
   ub4 rdba_kcbh                            @4        0x02404b25
   ub4 bas_kcbh                             @8        0x3c23c8b2
   ub2 wrp_kcbh                             @12       0x0b8c
   ub1 seq_kcbh                             @14       0x01
   ub1 flg_kcbh                             @15       0x02 (KCBHFDLC)
   ub2 chkval_kcbh                          @16       0x04b3
   ub2 spare3_kcbh                          @18       0x0000
BBED> m /x 11 offset 7184
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 7184 to 7199           Dba:0x00000000
------------------------------------------------------------------------
 110000c2 39b50002 05c40721 07280000
 <32 bytes per line>
BBED> undo
BBED> modify /x 00 filename 'E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF' block 19238. offset 7184.
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 7184 to 7199           Dba:0x00000000
------------------------------------------------------------------------
 000000c2 39b50002 05c40721 07280000
 <32 bytes per line>
BBED> m /x 11 offset 8174
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 8174 to 8189           Dba:0x00000000
------------------------------------------------------------------------
 1177772e 6f726173 6f732e63 6f6d0106
 <32 bytes per line>
BBED> sum
Check value for File 0, Block 19238:
current = 0x04b3, required = 0x04b3
--证明当flg_kcbh=2修改block之后chkval_kcbh依然为04b3，证明flg_kcbh不含(KCBHFCKV),
--修改block不会导致chkval_kcbh改变，也就是说,该block为启用db_block_checksum
--flg_kcbh=6的时候验证修改block导致的chkval_kcbh变化
BBED> m /x 06 offset 15
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets:   15 to   30           Dba:0x00000000
------------------------------------------------------------------------
 06b30400 00010000 00d86b01 00aec823
 <32 bytes per line>
--刚刚修改flg_kcbh=6,马上看到required非0
BBED> sum
Check value for File 0, Block 19238:
current = 0x04b3, required = 0x04da
BBED> sum apply
Check value for File 0, Block 19238:
current = 0x04da, required = 0x04da
--尝试修改block
BBED> m /x 22 offset 8174
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 8174 to 8189           Dba:0x00000000
------------------------------------------------------------------------
 2277772e 6f726173 6f732e63 6f6d0106
 <32 bytes per line>
--required发生改变
BBED> sum
Check value for File 0, Block 19238:
current = 0x04da, required = 0x04e9
BBED> sum apply
Check value for File 0, Block 19238:
current = 0x04e9, required = 0x04e9
--修改为以前值，验证required
BBED> m /x 11 offset 8174
 File: E:\APP\XIFENFEI\ORADATA\CDB\PDB\PDB_USERS01.DBF (0)
 Block: 19238            Offsets: 8174 to 8189           Dba:0x00000000
------------------------------------------------------------------------
 1177772e 6f726173 6f732e63 6f6d0106
 <32 bytes per line>
BBED> sum
Check value for File 0, Block 19238:
current = 0x04e9, required = 0x04da
BBED> sum apply
Check value for File 0, Block 19238:
current = 0x04da, required = 0x04da
--发现当block修改回来后，required值和以前一致(也就是说chkval_kcbh值还原)
--进步一说明chkval_kcbh取决于block内部值

通过相关测试db_block_checksum是在实例级别启动block checksum，但是具体到每个block是通过flg_kcbh来控制，而具体体现是在chkval_kcbh值上

One thought on “db_block_checksum实质是通过flg_kcbh来控制block checksum”

  1. 这个在研究块结构的时候发现了，但是没有仔细想
    KCBHFNEW BIT 0x01 // new block – zeroed data area
    KCBHFDLC BIT 0x02 // Delayed Logging Change advanced SCN/seq
    KCBHFCKV BIT 0x04 // ChecK Value saved – block xor’s to zero
    KCBHFTMP BIT 0x08 // Temporary block.
    0x06=0x02+0x04 KCBHFDLC+KCBHFCKV

    回复

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