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ASM Virtually addressed metadata-Active Change Directory

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dbsupport
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Active Change Directory简称ACD，是ASM的3号文件，我们都知道redo日志记录了数据文件数据块的每一次原子性变化，而ACD它描述了ASM元数据块每一次原子性变化，可以认为ACD是ASM实例的redo。redo根据database实例分为多个thread，同样ACD根据ASM实例也分为多个thread，每个thread为ACD分配了42个M，假如磁盘组AU为1M，那么thread 1使用0-41号extent，thread 2使用42-83号extent，以此类推

SQL> select PXN_KFFXP,XNUM_KFFXP,DISK_KFFXP,AU_KFFXP from x$kffxp where GROUP_KFFXP=2 and NUMBER_KFFXP=3 and XNUM_KFFXP<>2147483648;
 PXN_KFFXP XNUM_KFFXP DISK_KFFXP   AU_KFFXP
---------- ---------- ---------- ----------
         0          0          2          3        --thread 1 ACD的第一个逻辑extent
...
        41         41          0         16
        42         42          2       2469        --thread 2 ACD的第一个逻辑extent
...
        83         83          0       2483

84 rows selected.

PXN_KFFXP为物理extent号，XNUM_KFFXP为逻辑extent号

  • 对于external冗余磁盘组，XNUM_KFFXP=PXN_KFFXP
  • 对于normal冗余磁盘组，XNUM_KFFXP=trunc(PXN_KFFXP/2）
  • 对于high冗余磁盘组，XNUM_KFFXP=trunc(PXN_KFFXP/3）

需要注意的是对于元数据asm文件，normal磁盘组也有3份镜像，所以XNUM_KFFXP=trunc(PXN_KFFXP/3)，对于每一个thread的ACD的第一个AU的0号块，存放的是ACD checkpoint block，它记录着ASM磁盘组元数据的检查点信息，当磁盘组意外dismount，重新mount时，需要从ACD checkpoint的位置开始recover，这点与db实例的实例恢复类似。

NOTE: attached to recovery domain 2
Fri Sep 25 00:31:57 2020
NOTE: crash recovery of group SOLDATA will recover thread=1 ckpt=28.3507 domain=2 inc#=2 instnum=2
NOTE: crash recovery of group SOLDATA will recover thread=2 ckpt=39.8576 domain=2 inc#=4 instnum=1
NOTE: crash recovery of group SOLDATA will recover thread=3 ckpt=21.9043 domain=2 inc#=6 instnum=4
NOTE: crash recovery of group SOLDATA will recover thread=4 ckpt=22.6878 domain=2 inc#=12 instnum=3

每个thread的ACD checkpoint block之后的块都是Active change block，是真正存放ASM元数据块改动记录的地方，下面我们来看看ACD checkpoint block和Active change block存放的内容。

ACD checkpoint block：

[grid@rac1 ~]$ kfed read /dev/asmdisk-data6 aun=3
kfbh.endian:                          1 ; 0x000: 0x01
kfbh.hard:                          130 ; 0x001: 0x82
kfbh.type:                            7 ; 0x002: KFBTYP_ACDC
kfbh.datfmt:                          1 ; 0x003: 0x01
kfbh.block.blk:                       0 ; 0x004: blk=0
kfbh.block.obj:                       3 ; 0x008: file=3
kfbh.check:                  1111749672 ; 0x00c: 0x4243f428
kfbh.fcn.base:                        0 ; 0x010: 0x00000000
kfbh.fcn.wrap:                        0 ; 0x014: 0x00000000
kfbh.spare1:                          0 ; 0x018: 0x00000000
kfbh.spare2:                          0 ; 0x01c: 0x00000000
kfracdc.eyec[0]:                     65 ; 0x000: 0x41
kfracdc.eyec[1]:                     67 ; 0x001: 0x43
kfracdc.eyec[2]:                     68 ; 0x002: 0x44
kfracdc.eyec[3]:                     67 ; 0x003: 0x43
kfracdc.thread:                       1 ; 0x004: 0x00000001  --thread 1
kfracdc.lastAba.seq:         4294967295 ; 0x008: 0xffffffff
kfracdc.lastAba.blk:         4294967295 ; 0x00c: 0xffffffff
kfracdc.blk0:                         1 ; 0x010: 0x00000001
kfracdc.blks:                     10751 ; 0x014: 0x000029ff
kfracdc.ckpt.seq:                     5 ; 0x018: 0x00000005
kfracdc.ckpt.blk:                   659 ; 0x01c: 0x00000293
kfracdc.fcn.base:                  7936 ; 0x020: 0x00001f00
kfracdc.fcn.wrap:                     0 ; 0x024: 0x00000000
kfracdc.bufBlks:                    256 ; 0x028: 0x00000100
kfracdc.strt112.seq:                  2 ; 0x02c: 0x00000002
kfracdc.strt112.blk:                  0 ; 0x030: 0x00000000

[grid@rac1 ~]$ kfed read /dev/asmdisk-data6 aun=2469 blkn=0
kfbh.endian:                          1 ; 0x000: 0x01
kfbh.hard:                          130 ; 0x001: 0x82
kfbh.type:                            7 ; 0x002: KFBTYP_ACDC
kfbh.datfmt:                          1 ; 0x003: 0x01
kfbh.block.blk:                   10752 ; 0x004: blk=10752
kfbh.block.obj:                       3 ; 0x008: file=3
kfbh.check:                  1111747004 ; 0x00c: 0x4243e9bc
kfbh.fcn.base:                     7882 ; 0x010: 0x00001eca
kfbh.fcn.wrap:                        0 ; 0x014: 0x00000000
kfbh.spare1:                          0 ; 0x018: 0x00000000
kfbh.spare2:                          0 ; 0x01c: 0x00000000
kfracdc.eyec[0]:                     65 ; 0x000: 0x41
kfracdc.eyec[1]:                     67 ; 0x001: 0x43
kfracdc.eyec[2]:                     68 ; 0x002: 0x44
kfracdc.eyec[3]:                     67 ; 0x003: 0x43
kfracdc.thread:                       2 ; 0x004: 0x00000002     --thread 2
kfracdc.lastAba.seq:         4294967295 ; 0x008: 0xffffffff
kfracdc.lastAba.blk:         4294967295 ; 0x00c: 0xffffffff
kfracdc.blk0:                     10753 ; 0x010: 0x00002a01
kfracdc.blks:                     10751 ; 0x014: 0x000029ff
kfracdc.ckpt.seq:                     2 ; 0x018: 0x00000002
kfracdc.ckpt.blk:                     2 ; 0x01c: 0x00000002
kfracdc.fcn.base:                  7883 ; 0x020: 0x00001ecb
kfracdc.fcn.wrap:                     0 ; 0x024: 0x00000000
kfracdc.bufBlks:                    256 ; 0x028: 0x00000100
kfracdc.strt112.seq:                  2 ; 0x02c: 0x00000002
kfracdc.strt112.blk:                  0 ; 0x030: 0x00000000
  • KFBTYP_ACDC:ACD checkpoint
  • kfracdc.thread:ASM thread号
  • kfracdc.blk0：该thread的第一个Active change block块号
  • kfracdc.blks：该thread有多少个Active change block块，ASM元数据块大小为4k，10751个Active change block，再加上1个ACDC block，正好是42M即42个AU
  • kfracdc.ckpt.seq/blk:checkpoint ABA(ACD block address)，类似于db实例的checkpoint rba
  • kfracdc.fcn.base/wrap:checkpoint FCN，类似于db实例的checkpoint scn

Active change block：

[grid@rac1 ~]$ kfed read /dev/asmdisk-data6 aun=3 blkn=4|more
kfbh.endian:                          1 ; 0x000: 0x01
kfbh.hard:                          130 ; 0x001: 0x82
kfbh.type:                            8 ; 0x002: KFBTYP_CHNGDIR
kfbh.datfmt:                          1 ; 0x003: 0x01
kfbh.block.blk:                       4 ; 0x004: blk=4
kfbh.block.obj:                       3 ; 0x008: file=3
kfbh.check:                  4174549927 ; 0x00c: 0xf8d293a7
kfbh.fcn.base:                       80 ; 0x010: 0x00000050
kfbh.fcn.wrap:                        0 ; 0x014: 0x00000000
kfbh.spare1:                          0 ; 0x018: 0x00000000
kfbh.spare2:                          0 ; 0x01c: 0x00000000
kfracdb.aba.seq:                      2 ; 0x000: 0x00000002
kfracdb.aba.blk:                      3 ; 0x004: 0x00000003
kfracdb.ents:                        77 ; 0x008: 0x004d
kfracdb.ub2spare:                     0 ; 0x00a: 0x0000
kfracdb.lge[0].valid:                 1 ; 0x00c: V=1 B=0 M=0
kfracdb.lge[0].chgCount:              1 ; 0x00d: 0x01
kfracdb.lge[0].len:                  52 ; 0x00e: 0x0034
kfracdb.lge[0].kfcn.base:            81 ; 0x010: 0x00000051
kfracdb.lge[0].kfcn.wrap:             0 ; 0x014: 0x00000000
kfracdb.lge[0].bcd[0].kfbl.blk:     417 ; 0x018: blk=417
kfracdb.lge[0].bcd[0].kfbl.obj:       4 ; 0x01c: file=4
kfracdb.lge[0].bcd[0].kfcn.base:     81 ; 0x020: 0x00000051
kfracdb.lge[0].bcd[0].kfcn.wrap:      0 ; 0x024: 0x00000000
kfracdb.lge[0].bcd[0].oplen:          4 ; 0x028: 0x0004
kfracdb.lge[0].bcd[0].blkIndex:     161 ; 0x02a: 0x00a1
kfracdb.lge[0].bcd[0].flags:         30 ; 0x02c: F=0 N=1 F=1 L=1 V=1 A=0 C=0
kfracdb.lge[0].bcd[0].opcode:       208 ; 0x02e: 0x00d0
kfracdb.lge[0].bcd[0].kfbtyp:         0 ; 0x030: KFBTYP_INVALID
kfracdb.lge[0].bcd[0].redund:        17 ; 0x031: SCHE=0x1 NUMB=0x1
kfracdb.lge[0].bcd[0].pad:        63903 ; 0x032: 0xf99f
kfracdb.lge[0].bcd[0].KFRCOD_NEW:    16 ; 0x034: 0x00000010
kfracdb.lge[0].bcd[0].au[0]:         17 ; 0x038: 0x00000011
kfracdb.lge[0].bcd[0].disks[0]:       2 ; 0x03c: 0x0002
kfracdb.lge[1].valid:                 1 ; 0x040: V=1 B=0 M=0
kfracdb.lge[1].chgCount:              1 ; 0x041: 0x01
kfracdb.lge[1].len:                  52 ; 0x042: 0x0034
kfracdb.lge[1].kfcn.base:            82 ; 0x044: 0x00000052
kfracdb.lge[1].kfcn.wrap:             0 ; 0x048: 0x00000000
kfracdb.lge[1].bcd[0].kfbl.blk:     418 ; 0x04c: blk=418
kfracdb.lge[1].bcd[0].kfbl.obj:       4 ; 0x050: file=4
kfracdb.lge[1].bcd[0].kfcn.base:     82 ; 0x054: 0x00000052
kfracdb.lge[1].bcd[0].kfcn.wrap:      0 ; 0x058: 0x00000000
kfracdb.lge[1].bcd[0].oplen:          4 ; 0x05c: 0x0004
kfracdb.lge[1].bcd[0].blkIndex:     162 ; 0x05e: 0x00a2
kfracdb.lge[1].bcd[0].flags:         30 ; 0x060: F=0 N=1 F=1 L=1 V=1 A=0 C=0
--More--
  • KFBTYP_CHNGDIR：Active change block
  • kfracdb.aba.seq/blk：ACD block address
  • kfracdb.ents：此Active change block有多少个lge(ACD redo log record)
  • kfracdb.lge：ACD redo log record，类似于db实例redo的重做记录
  • lge.chgCount:该lge有多少BCD(block change descriptor),BCD类似于db实例redo的重做记录的改动向量
  • lge.len:lge的size
  • lge.kfcn.base/wrap:lge的fcn,类似于db实例redo生成重做记录的SCN
  • lge.chgCount:该lge有多少BCD(block change descriptor)
  • lge.bcd：block change descriptor，类似于db实例redo的重做记录的改动向量，描述了每一次元数据块的改动

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