SQLServer2012 表IAM存储结构探究
Author:zfive5(zidong)
Email: zfive5@163.com
引子
国庆节期间，一直在翻阅《程序猿的自我修养—链接、装载与库》。这本给我的感觉是越看越乱，但总的来说还不错。一句话--优秀程序猿就应该知道每个字节的意义。
看此书前的两本《深入解析SQLServer2008》和《Microsoft SQL Server 2005技术内幕：存储引擎》对IAM解读都是点到为止，让我满脑袋是一堆问号，内心特别想通过IAM找到数据库里的数据。这样才干让我为性能优化打开思路。
尽管两本书有些内容重叠，但它们绝对值得收藏和慢慢研读。
正文
分析样例与数据
通过以下SQL语句建分析的样例库和数据
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CREATE TABLE[dbo].[Table6]( [a] [int] IDENTITY(1,1)NOTNULL, [b] [char](8000)NULL, [c] [int] NULL ) ON[PRIMARY]
DECLARE @V1 INT SET @V1=1 WHILE @V1<1000000 BEGIN insert intoTable6(B,C)values(REPLICATE('c',8000),1) SET @V1=@V1+1 END
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SQL查询后数据例如以下图：
两个命令
两个命令各自是DBCC IND和 DBCC PAGE
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DBCC IND 命令用于查询一个存储对象的内部存储结构信息，该命令有4个參数, 前3个參数必须指定。语法例如以下： DBCC IND ( { 'dbname' | dbid }, { 'objname' | objid },{ nonclustered indid | 1 | 0 | -1 | -2 } [, partition_number] ) 第一个參数是数据库名或数据库ID。 第二个參数是数据库中的对象名或对象ID，对象能够是表或者索引视图。 第三个參数是一个非聚集索引ID或者 1, 0, 1, or 2. 值的含义： 0: 仅仅显示对象的in-row data页和 in-row IAM 页。 1: 显示对象的所有页, 包括IAM 页, in-row数据页, LOB 数据页row-overflow 数据页 . 假设请求的对象含有聚集所以则索引页也包括。 -1: 显示所有IAM页,数据页, 索引页 也包含 LOB 和row-overflow 数据页。 -2: 显示所有IAM页。 Nonclustered index ID:显示索引的所有 IAM页, data页和索引页。包括LOB和 row-overflow数据页。 为了兼容sql server 2000,第四个參数是可选的,该參数用于指定一个分区号.假设不给定值或者给定0, 则显示所有分区数据。.
DBCC Page ({dbid|dbname},filenum,pagenum[,printopt]) 须要开启3604跟踪标志. |
接下来通过运行
dbcc ind('A','Table6',-1)，
能够看到例如以下图数据：
1：35646 Table6第1个IAM page
通过运行：
dbcc traceon(3604)
dbcc page('A',1,35646,1)
能够得到全部的：
1：35646 Table6第1个IAM page
1：35662 Table6第2个IAM page
1：35663 Table6第3个IAM page
1：1533712 Table6第4个IAM page
每个IAM page 都能够通过
dbcc traceon(3604)
dbcc page('A',1,35646,1)
dbcc page('A',1,35662,1)
dbcc page('A',1,35663,1)
dbcc page('A',1,1533712,1)
看到内部的数据，当中1,35646 数据例如以下：
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DBCC 运行完成。假设 DBCC 输出了错误信息，请与系统管理员联系。
PAGE: (1:35646)
BUFFER:
BUF @0x000000047240BF40
bpage = 0x0000000286FAE000 bhash = 0x0000000000000000 bpageno = (1:35646) bdbid = 7 breferences = 0 bcputicks = 0 bsampleCount = 0 bUse1 = 58643 bstat = 0x9 blog = 0x5adb215a bnext = 0x0000000000000000
PAGE HEADER:
Page @0x0000000286FAE000
m_pageId = (1:35646) m_headerVersion = 1 m_type = 10 m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x200 m_objId (AllocUnitId.idObj) = 98 m_indexId (AllocUnitId.idInd) = 256 Metadata: AllocUnitId = 72057594044350464 Metadata: PartitionId = 72057594040025088 Metadata: IndexId = 0 Metadata: ObjectId = 1541580530 m_prevPage = (0:0) m_nextPage = (1:35662) pminlen = 90 m_slotCnt = 2 m_freeCnt = 6 m_freeData = 8182 m_reservedCnt = 0 m_lsn = (1236:22589:9) m_xactReserved = 0 m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = 2069893598 DB Frag ID = 1
Allocation Status
GAM (1:2) = ALLOCATED SGAM (1:3) = NOT ALLOCATED PFS (1:32352) = 0x70 IAM_PG MIXED_EXT ALLOCATED 0_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 = Record Size = 94
Memory Dump @0x00000000139FA060
0000000000000000: 00005e00 00000000 00000000 00000000 00000000 ..^................. 0000000000000014: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000028: 00000000 01003d8b 00000100 3f8b00000100488b ......=.....? .....H. 000000000000003C: 00000100 498b000001004a8b 00000100 4b8b0000 ....I.....J.....K... 0000000000000050: 01004c8b 00000100 4d8b0000 0100 ..L.....M.....
Slot 1, Offset 0xbe, Length 7992, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes = Record Size = 7992
Memory Dump @0x00000000139FA0BE
0000000000000000: 0000381f 00000000 00000000 00000000 00000000 ..8................. 0000000000000014: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000028: 00000000 00000000 00000000 00000000 00000000 .................... 000000000000003C: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000050: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000064: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000078: 00000000 00000000 00000000 00000000 00000000 .................... 000000000000008C: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000000A0: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000000B4: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000000C8: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000000DC: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000000F0: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000104: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000118: 00000000 00000000 00000000 00000000 00000000 .................... 000000000000012C: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000140: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000154: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000168: 00000000 00000000 00000000 00000000 00000000 .................... 000000000000017C: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000190: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000001A4: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000001B8: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000001CC: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000001E0: 00000000 00000000 00000000 00000000 00000000 .................... 00000000000001F4: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000208: 00000000 00000000 00000000 00000000 00000000 .................... 000000000000021C: 00000000 00000000 00000000 00000000 00000000 .................... 0000000000000230: 00fcffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000244: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000258: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 000000000000026C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000280: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000294: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 00000000000002A8: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 00000000000002BC: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 00000000000002D0: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 00000000000002E4: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 00000000000002F8: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 000000000000030C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000320: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000334: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000000348: ffffffff ffffffff ffffffff ffffffff ffffffff .................... …… 0000000000001CE8: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001CFC: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D10: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D24: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D38: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D4C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D60: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D74: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D88: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001D9C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001DB0: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001DC4: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001DD8: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001DEC: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E00: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E14: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E28: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E3C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E50: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E64: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E78: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001E8C: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001EA0: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001EB4: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001EC8: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001EDC: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001EF0: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001F04: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001F18: ffffffff ffffffff ffffffff ffffffff ffffffff .................... 0000000000001F2C: ffffffff ffffffff ffffffff ............
DBCC 运行完成。 假设 DBCC 输出了错误信息，请与系统管理员联系。
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样例分析
每个IAM有两个SLOT，第1个IAM中第1个SLOT 中有8个页指针例如以下表（其他IAM第1个SLOT对如今的我还是问号)
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指针(二进制) |
页指针（十进制） |
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01003d8b 0000 0100 3f8b0000 0100488b 0000 0100 498b0000 01004a8b 0000 0100 4b8b0000 01004c8b 0000 0100 4d8b0000 |
1 35645 1 35647 1 35656 1 35657 1 35658 1 35659 1 35660 1 35661 |
Table6的每个IAM Page第2个SLOT。去除前4个字节，接下来是每BIT都是一个代表1个Extend（8个连续的Page）是否被本数据对象使用:
1:被本对象占用，
0:没有被本对象占用
以下列出Table6 中的每个IAM 第2个SLOT 部分重要数据
第一个IAM
dbcc traceon(3604)
dbcc page('A',1,35646,1)
0000000000000000: 0000381f 00000000 0000000000000000 00000000
……
0000000000000230: 00fcffff ffffffff ffffffffffffffff ffffffff
……
0000000000001F2C: ffffffff ffffffff ffffffff
FE: 1111 1100
((231H-4)*8-2)*8=35664
如图蓝色框部分
第二个IAM
dbcc traceon(3604)
dbcc page('A',1,35662,1)
0000000000000000: 0000381f feffffff ffffffffffffffff ffffffff
……
0000000000001F2C: ffffffff ffffffff ffffffff
FE: 1111 1110
((1F2CH+12-4)*8+1)*8=511240
如图蓝色框部分
第三个IAM
dbcc traceon(3604)
dbcc page('A',1,35663,1)
0000000000000000: 0000381f feffffff ffffffffffffffff ffffffff
……
0000000000001F2C: ffffffff ffffffff ffffffff
FE: 1111 1110
((1F2CH+12-4+1FC2H+12-4)*8+1)*8=1022472
如图蓝色框部分
第四个IAM
dbcc traceon(3604)
dbcc page('A',1,1533712,1)
0000000000000000: 0000381f faffffff ffffffffffffffff ffffffff
…….
00000000000005B4: ffffffff ffffffff ffffffff ffffff0000000000
FE: 1111 1010
((1F2CH+12-4+1FC2H+12-4+1F2CH+12-4)*8+1)*8=1533704
如图第一个蓝色框部分。低位第2个"1" BIT。代表了第二个篮框
某条记
然后通过DBCCPAGE 能够得到了真正的数据记录，比如最后一条记录
dbcc traceon(3604)
dbcc page('A',1,1627839,1)
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DBCC 运行完成。假设 DBCC 输出了错误信息，请与系统管理员联系。
PAGE: (1:1627839)
BUFFER:
BUF @0x000000046F48EC40
bpage = 0x000000045C6FC000 bhash = 0x0000000000000000 bpageno = (1:1627839) bdbid = 7 breferences = 0 bcputicks = 70 bsampleCount = 1 bUse1 = 32444 bstat = 0x9 blog = 0x15ab215a bnext = 0x0000000000000000
PAGE HEADER:
Page @0x000000045C6FC000
m_pageId = (1:1627839) m_headerVersion = 1 m_type = 1 m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x8200 m_objId (AllocUnitId.idObj) = 98 m_indexId (AllocUnitId.idInd) = 256 Metadata: AllocUnitId = 72057594044350464 Metadata: PartitionId = 72057594040025088 Metadata: IndexId = 0 Metadata: ObjectId = 1541580530 m_prevPage = (0:0) m_nextPage = (0:0) pminlen = 8012 m_slotCnt = 1 m_freeCnt = 79 m_freeData = 8111 m_reservedCnt = 0 m_lsn = (2320:17330:8) m_xactReserved = 0 m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = 194973556 DB Frag ID = 1
Allocation Status
GAM (1:1533696) = ALLOCATED SGAM (1:1533697) = NOT ALLOCATED PFS (1:1625688) = 0x44 ALLOCATED 100_PCT_FULL DIFF (1:1533702) = CHANGED ML (1:1533703) = NOT MIN_LOGGED
DATA:
Slot 0, Offset 0x60, Length 8015, DumpStyle BYTE
Record Type = PRIMARY_RECORD Record Attributes = NULL_BITMAP Record Size = 8015
Memory Dump @0x000000001214A060
0000000000000000: 10004c1f 944a1800 63636363 63636363 63636363 ..L..J..cccccccccccc 0000000000000014: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000000028: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 000000000000003C: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000000050: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000000064: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc …… 0000000000001F04: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000001F18: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000001F2C: 63636363 63636363 63636363 63636363 63636363 cccccccccccccccccccc 0000000000001F40: 63636363 63636363 01000000 030000 cccccccc.......
OFFSET TABLE:
Row - Offset 0 (0x0) - 96 (0x60)
DBCC 运行完成。 假设 DBCC 输出了错误信息，请与系统管理员联系。
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结论
IAM的结构已经OK 90%，但那10%还是继续问号。期待不远的将来迎来解惑之篇
