ASSM采用3级位图，第一个extent至少有3个元数据块，L1 – L2 – header(包含L3)
段头 & L3
Extent control: 存储HHWM信息
Header control: 记录三级位图的基本信息，其中L2 hint for insert为搜索可用空间的起始位置
Extent table/Auxillary extent map: 维护extent map信息
buffer tsn: 115 rdba: 0x11227ca3 (68/2260131)
scn: 0x0860.07f11dac seq: 0x01 flg: 0x04 tail: 0x1dac2301
frmt: 0x02 chkval: 0x7157 type: 0x23=PAGETABLE SEGMENT HEADER
Hex dump of block: st=0, typ_found=1
Extent Control Header
--------------------描述HHWM---------------------------------------------
Extent Header:: spare1: 0 spare2: 0 #extents: 23 #blocks: 1024
last map 0x00000000 #maps: 0 offset: 2716
Highwater:: 0x113a3e09 ext#: 22 blk#: 128 ext size: 128 --高水位线块号/所在extent/该extent块数
#blocks in seg. hdr's freelists: 0
#blocks below: 1000
mapblk 0x00000000 offset: 22
Unlocked
-------------------描述LHWM-------------------------------------
Low HighWater Mark :
Highwater:: 0x113a3e09 ext#: 22 blk#: 128 ext size: 128
#blocks in seg. hdr's freelists: 0
#blocks below: 1024
mapblk 0x00000000 offset: 22
Level 1 BMB for High HWM block: 0x113a3d8a
Level 1 BMB for Low HWM block: 0x113a3d8a
--------------------------------------------------------
Segment Type: 1 nl2: 1 blksz: 8192 fbsz: 0
L2 Array start offset: 0x00001434
First Level 3 BMB: 0x00000000
L2 Hint for inserts: 0x11227ca2 – 搜索L2 BMB的起始位置，insert需要使用
Last Level 1 BMB: 0x113a3d8a
Last Level II BMB: 0x11227ca2
Last Level III BMB: 0x00000000
Map Header:: next 0x00000000 #extents: 23 obj#: 345420 flag: 0x20000000
Inc # 0
Extent Map--以(dba, len)形式存储extent基本信息，start DBA + length
-----------------------------------------------------------------
0x11227ca1 length: 8
0x11227ca9 length: 8
0x11227cb1 length: 8
.............
0x11400109 length: 128
0x113a3d09 length: 128
0x11400189 length: 128
0x113a3d89 length: 128
Auxillary Map：extent no + L1 BMB of first DBA + first DBA in extent(extent 0前3个块存储metadata)
--------------------------------------------------------
Extent 0 : L1 dba: 0x11227ca1 Data dba: 0x11227ca4
Extent 1 : L1 dba: 0x11227ca1 Data dba: 0x11227ca9
Extent 2 : L1 dba: 0x11227cb1 Data dba: 0x11227cb2
Extent 3 : L1 dba: 0x11227cb1 Data dba: 0x11227cb9
.............
Extent 19 : L1 dba: 0x11400109 Data dba: 0x1140010b
Extent 20 : L1 dba: 0x113a3d09 Data dba: 0x113a3d0b
Extent 21 : L1 dba: 0x11400189 Data dba: 0x1140018b
Extent 22 : L1 dba: 0x113a3d89 Data dba: 0x113a3d8b
--------------------------------------------------------
Second Level Bitmap block DBAs
--------------------------------------------------------
DBA 1: 0x11227ca2
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