mysql truncate 原理_深入解析：TRUNCATE TABLE 的内部原理解析与恢复思路

segment header dump：

Extent Control Header

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

Extent Header:: spare1: 0      spare2: 0      #extents: 28     #blocks: 1664

last map  0x00000000  #maps: 0      offset: 2716

Highwater::  0x01405b83  ext#: 27     blk#: 3      ext size: 128

#blocks in seg. hdr's freelists: 0

#blocks below: 1539

mapblk  0x00000000  offset: 27

Unlocked

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

Low HighWater Mark :

Highwater::  0x01405b83  ext#: 27     blk#: 3      ext size: 128

#blocks in seg. hdr's freelists: 0

#blocks below: 1539

mapblk  0x00000000  offset: 27

Level 1 BMB for High HWM block: 0x01405b80

Level 1 BMB for Low HWM block: 0x01405b80

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

Segment Type: 1 nl2: 1      blksz: 8192   fbsz: 0

L2 Array start offset:  0x00001434

First Level 3 BMB:  0x00000000

L2 Hint for inserts:  0x01400769

Last Level 1 BMB:  0x01405b81

Last Level II BMB:  0x01400769

Last Level III BMB:  0x00000000

Map Header:: next  0x00000000  #extents: 28   obj#: 16840  flag: 0x10000000

Inc # 0

Extent Map

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

0x01400768  length: 8

0x01402f48  length: 8

0x01402f50  length: 8

0x01402f58  length: 8

0x01402f60  length: 8

0x01402f68  length: 8

0x01402f70  length: 8

0x01402f78  length: 8

0x01402e80  length: 8

0x01402e88  length: 8

0x01402e90  length: 8

0x01402e98  length: 8

0x01402ea0  length: 8

0x01402ea8  length: 8

0x01402eb0  length: 8

0x01402eb8  length: 8

0x01403f80  length: 128

0x01404000  length: 128

0x01404080  length: 128

0x01404180  length: 128

0x01405800  length: 128

0x01405880  length: 128

0x01405900  length: 128

0x01405980  length: 128

0x01405a00  length: 128

0x01405a80  length: 128

0x01405b00  length: 128

0x01405b80  length: 128

Auxillary Map

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

Extent 0     :  L1 dba:  0x01400768 Data dba:  0x0140076b

Extent 1     :  L1 dba:  0x01400768 Data dba:  0x01402f48

Extent 2     :  L1 dba:  0x01402f50 Data dba:  0x01402f51

Extent 3     :  L1 dba:  0x01402f50 Data dba:  0x01402f58

Extent 4     :  L1 dba:  0x01402f60 Data dba:  0x01402f61

Extent 5     :  L1 dba:  0x01402f60 Data dba:  0x01402f68

Extent 6     :  L1 dba:  0x01402f70 Data dba:  0x01402f71

Extent 7     :  L1 dba:  0x01402f70 Data dba:  0x01402f78

Extent 8     :  L1 dba:  0x01402e80 Data dba:  0x01402e81

Extent 9     :  L1 dba:  0x01402e80 Data dba:  0x01402e88

Extent 10    :  L1 dba:  0x01402e90 Data dba:  0x01402e91

Extent 11    :  L1 dba:  0x01402e90 Data dba:  0x01402e98

Extent 12    :  L1 dba:  0x01402ea0 Data dba:  0x01402ea1

Extent 13    :  L1 dba:  0x01402ea0 Data dba:  0x01402ea8

Extent 14    :  L1 dba:  0x01402eb0 Data dba:  0x01402eb1

Extent 15    :  L1 dba:  0x01402eb0 Data dba:  0x01402eb8

Extent 16    :  L1 dba:  0x01403f80 Data dba:  0x01403f82

Extent 17    :  L1 dba:  0x01404000 Data dba:  0x01404002

Extent 18    :  L1 dba:  0x01404080 Data dba:  0x01404082

Extent 19    :  L1 dba:  0x01404180 Data dba:  0x01404182

Extent 20    :  L1 dba:  0x01405800 Data dba:  0x01405802

Extent 21    :  L1 dba:  0x01405880 Data dba:  0x01405882

Extent 22    :  L1 dba:  0x01405900 Data dba:  0x01405902

Extent 23    :  L1 dba:  0x01405980 Data dba:  0x01405982

Extent 24    :  L1 dba:  0x01405a00 Data dba:  0x01405a02

Extent 25    :  L1 dba:  0x01405a80 Data dba:  0x01405a82

Extent 26    :  L1 dba:  0x01405b00 Data dba:  0x01405b02

Extent 27    :  L1 dba:  0x01405b80 Data dba:  0x01405b82

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

Second Level Bitmap block DBAs

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

DBA 1:   0x01400769