SGAM页面
PAGE: (1:3)
BUFFER:
BUF @0x0358A7F4
bpage = 0x062AE000 bhash = 0x00000000 bpageno = (1:3)
bdbid = 8 breferences = 3 bUse1 = 14428
bstat = 0xc00009 blog = 0x21212159 bnext = 0x00000000
PAGE HEADER:
Page @0x062AE000
m_pageId = (1:3) m_headerVersion = 1 m_type = 9
m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x200
m_objId (AllocUnitId.idObj)=99 m_indexId (AllocUnitId.idInd)=0 Metadata: AllocUnitId=6488064
Metadata: PartitionId = 0 Metadata: IndexId = 0 Metadata: ObjectId = 99
m_prevPage = (0:0) m_nextPage = (0:0) pminlen = 90
m_slotCnt = 2 m_freeCnt = 6 m_freeData = 8182
m_reservedCnt = 0 m_lsn = (18:435:5) m_xactReserved = 0
m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = 177043542
Allocation Status
GAM (1:2)=ALLOCATED SGAM (1:3)=NOT ALLOCATED PFS(1:1)=0x44 ALLOCATED 100_PCT_FULL
DIFF (1:6) = CHANGED ML (1:7) = NOT MIN_LOGGED
DATA:
Slot 0, Offset 0x60, Length 94, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes =
Memory Dump @0x4F32C060
00000000: 00005e00 00000000 00000000 00000000 ?..^.............
00000010: 00000000 00000000 00000000 00000000 ?................
00000020: 00000000 00000000 00000000 00000000 ?................
00000030: 00000000 00000000 00000000 00000000 ?................
00000040: 00000000 00000000 00000000 00000000 ?................
00000050: 00000000 00000000 00000000 0000??????..............
Slot 1, Offset 0xbe, Length 7992, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes =
Memory Dump @0x4F32C0BE
00000000: 0000381f 20ee2000 00000000 00000000 ?..8. . .........
00000010: 00000000 00000000 00000000 00000000 ?................
00001F30: 00000000 00000000 ???????????????????........
BUFFER:
BUF @0x0358A7F4
bpage = 0x062AE000 bhash = 0x00000000 bpageno = (1:3)
bdbid = 8 breferences = 3 bUse1 = 14428
bstat = 0xc00009 blog = 0x21212159 bnext = 0x00000000
PAGE HEADER:
Page @0x062AE000
m_pageId = (1:3) m_headerVersion = 1 m_type = 9
m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x200
m_objId (AllocUnitId.idObj)=99 m_indexId (AllocUnitId.idInd)=0 Metadata: AllocUnitId=6488064
Metadata: PartitionId = 0 Metadata: IndexId = 0 Metadata: ObjectId = 99
m_prevPage = (0:0) m_nextPage = (0:0) pminlen = 90
m_slotCnt = 2 m_freeCnt = 6 m_freeData = 8182
m_reservedCnt = 0 m_lsn = (18:435:5) m_xactReserved = 0
m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = 177043542
Allocation Status
GAM (1:2)=ALLOCATED SGAM (1:3)=NOT ALLOCATED PFS(1:1)=0x44 ALLOCATED 100_PCT_FULL
DIFF (1:6) = CHANGED ML (1:7) = NOT MIN_LOGGED
DATA:
Slot 0, Offset 0x60, Length 94, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes =
Memory Dump @0x4F32C060
00000000: 00005e00 00000000 00000000 00000000 ?..^.............
00000010: 00000000 00000000 00000000 00000000 ?................
00000020: 00000000 00000000 00000000 00000000 ?................
00000030: 00000000 00000000 00000000 00000000 ?................
00000040: 00000000 00000000 00000000 00000000 ?................
00000050: 00000000 00000000 00000000 0000??????..............
Slot 1, Offset 0xbe, Length 7992, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes =
Memory Dump @0x4F32C0BE
00000000: 0000381f 20ee2000 00000000 00000000 ?..8. . .........
00000010: 00000000 00000000 00000000 00000000 ?................
00001F30: 00000000 00000000 ???????????????????........
以下为DBCC PAGE(TESTDB,1,3,3)得到的相关信息，有兴趣的可以和20ee20做一下对比。
(1:0) - (1:32) = NOT ALLOCATED
(1:40) - = ALLOCATED
(1:48) - (1:64) = NOT ALLOCATED
(1:72) - (1:88) = ALLOCATED
(1:96) - = NOT ALLOCATED
(1:104) - (1:120) = ALLOCATED
(1:128) - (1:160) = NOT ALLOCATED
(1:168) - = ALLOCATED
(1:176) - (1:272) = NOT ALLOCATED
(1:40) - = ALLOCATED
(1:48) - (1:64) = NOT ALLOCATED
(1:72) - (1:88) = ALLOCATED
(1:96) - = NOT ALLOCATED
(1:104) - (1:120) = ALLOCATED
(1:128) - (1:160) = NOT ALLOCATED
(1:168) - = ALLOCATED
(1:176) - (1:272) = NOT ALLOCATED
最后让我们用Internals Viewer插件看一下SGAM页的全貌吧。
总结一下，关于GAM和SGAM页比较困难的地方：
1、 关于GAM和SGAM页中的BUFFER信息基本无法理解，也找不到相关材料。
2、 PAGE HEADER的部分信息和Slot 0中的一部分信息，也无法找到相关材料。
3、 SGAM页中的NOT ALLOCATED实际上是统一类型区或者已使用完的混合类型的区，而ALLOCATED实际上为含有自由页面的混合区。
4、 GAM页中0代表已分配，1代表自由区;和一般的标志位的含义刚好相反。
5、 GAM和SGAM实际上只分配了280个页面，即35个区;显示出来的数据内容虽然很多，但后面的分区信息实际上是不存在的。
6、 GAM和SGAM通过DBCC的printopt为3的属性显示出来的页面分配信息看似是断号的。
7、 GAM和SGAM的区信息的字节是通过二级制反转得到的。
GAM和SGAM页的总的大小为8192个字节;文件头为96个字节，slot 0为94个字节，slot 1的头部的系统信息为4个字节，尾部的系统信息为10个字节，所以有效存储应为7988个字节，63904个区，511230个页;事实上当数据文件超过约4G的时候，我们将能在第511232页、 第511233页分别找到其对应的GAM、SGAM页面。
