SQL Server通过File Header Page来进行Crash Recovery
看了盖总的一篇文章
http://www.eygle.com/archives/2008/11/oracle_internals_preface.html
数据文件的第一个Block记录了重要的检查点、SCN等信息，这些信息在启动时要被读取，这里就是这样一种体现。
我们看一下SQL Server的情况，使用DBCC fileheader命令来读取file header page，编号为10是我的一个用户库SSS的数据库ID
环境：SQL Server2012 64位
SELECT DB_ID('sss')DBCC fileheader(10)
（图一）
（图二）
（图三）
（图四）
从上面的图大家应该发现一些规律
RecoveryForkLSN：Cash Recovery的时候需要调用的lsn，也是RedoStartLSN：27000000027100001
ReadOnlyLsn：只读模式数据库
ReadWriteLsn：读写模式数据库
因为file header page是每个数据库的mdf文件的第一个页面，启动的过程里面其实最重要也是最耗时就是数据库redo和undo过程
所以把Redo Start LSN放在file header page也就不无道理了，数据库一启动马上就读取LSN信息，然后到LDF文件里读取日志
数据库第0页:file header page
数据库第1页：PFS (Page Free Space) ,也叫页面自由空间
数据库第2页：GAM 全局分配映射(Global Allocation Map，GAM)页面
数据库第3页：SGAM 共享全局分配映射(Shared Global Allocation Map，SGAM)页面
第4页没有数据
第5页没有数据
数据库第6页：DCM 差异变更(Differential Changed Map，DCM)页面
数据库第7页：BCM 批量更改映射（Bulk Changed Map）页面
数据库第8页：sys.sysqnames 存在于每个数据库中。
数据库第9页：boot page 数据库根据这个页面的信息来启动的
boot page是放在第9页不是放在第0页，为什麽呢？因为数据库先要进行Cash Recovery才能启动啊
--看一下file header pageDBCC TRACEON(3604,-1)GODBCC PAGE([sss],1,0,3)GO
DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。PAGE: (1:0)BUFFER:BUF @0x00000002FDABA800bpage = 0x00000002EFF88000 bhash = 0x0000000000000000 bpageno = (1:0)bdbid = 10 breferences = 0 bcputicks = 88bsampleCount = 1 bUse1 = 36811 bstat = 0x9blog = 0x15ab215a bnext = 0x0000000000000000 PAGE HEADER:Page @0x00000002EFF88000m_pageId = (1:0) m_headerVersion = 1 m_type = 15m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x208m_objId (AllocUnitId.idObj) = 99 m_indexId (AllocUnitId.idInd) = 0 Metadata: AllocUnitId = 6488064Metadata: PartitionId = 0 Metadata: IndexId = 0 Metadata: ObjectId = 99m_prevPage = (0:0) m_nextPage = (0:0) pminlen = 0m_slotCnt = 1 m_freeCnt = 7029 m_freeData = 7551m_reservedCnt = 0 m_lsn = (878:901:1) m_xactReserved = 0m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = -582568961DB Frag ID = 1 Allocation StatusGAM (1:2) = ALLOCATED SGAM (1:3) = NOT ALLOCATED PFS (1:1) = 0x44 ALLOCATED 100_PCT_FULLDIFF (1:6) = CHANGED ML (1:7) = NOT MIN_LOGGED File Header Data:Record Type = PRIMARY_RECORD Record Attributes = NULL_BITMAP VARIABLE_COLUMNSRecord Size = 1065 Memory Dump @0x000000000D1BB9560000000000000000: 30000800 00000000 31000000 00000000 002e007f 0.......1...........0000000000000014: 007f0081 00830087 008b008f 0093009d 00a700b1 ....................0000000000000028: 00b100b5 00b900bd 00c100cb 00e700f1 00fb0005 ....................000000000000003C: 0115011f 012f0133 013d013d 01430153 01530153 ...../.3.=.=.C.S.S.S0000000000000050: 01530153 01530153 01630163 0163016d 01770193 .S.S.S.S.c.c.c.m.w..0000000000000064: 019d01ad 01c901d1 012904c5 cbddcf11 44c34889 .........)......D.H.0000000000000078: 52cc552b 3eba7601 00010080 c00500ff ffffff80 R.U+>.v.............000000000000008C: 00000000 00000000 00000000 00000000 00000000 ....................00000000000000A0: 00000000 00000000 00000000 00000000 00800100 ....................00000000000000B4: 00000000 00ffffff ff000200 001b0000 000f0100 ....................00000000000000C8: 0001001b 0000000f 01000001 00000053 d02a7787 ...............S.*w.00000000000000DC: 3ec94e97 926f64fe 3febf81b 000000c3 000000b2 >.N..od.?...........00000000000000F0: 00000000 00000000 0000006e 0300006d 0300002e ...........n...m....0000000000000104: 00284a9c 892994c1 4692f4f1 e3c51d34 90000000 .(J..)..F......4....0000000000000118: 00000000 00000014 51b676d9 b1a34abc c0185ae9 ........Q.v...J...Z.000000000000012C: 6fccb108 0000001b 0000000f 01000001 00730073 o................s.s0000000000000140: 0073006a 49d8681b 194f469a 40c068d8 57651953 .s.jI.h..OF.@.h.We.S0000000000000154: d02a7787 3ec94e97 926f64fe 3febf800 00000000 .*w.>.N..od.?.......0000000000000168: 00000000 00000000 00000000 00000000 00000000 ....................000000000000017C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000190: 0000001b 000000c3 000000b2 006a49d8 681b194f .............jI.h..O00000000000001A4: 469a40c0 68d85765 19000000 00000000 00000000 F.@.h.We............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: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000244: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000258: 00000000 00000000 00000000 00000000 00000000 ....................000000000000026C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000280: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000294: 00000000 00000000 00000000 00000000 00000000 ....................00000000000002A8: 00000000 00000000 00000000 00000000 00000000 ....................00000000000002BC: 00000000 00000000 00000000 00000000 00000000 ....................00000000000002D0: 00000000 00000000 00000000 00000000 00000000 ....................00000000000002E4: 00000000 00000000 00000000 00000000 00000000 ....................00000000000002F8: 00000000 00000000 00000000 00000000 00000000 ....................000000000000030C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000320: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000334: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000348: 00000000 00000000 00000000 00000000 00000000 ....................000000000000035C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000370: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000384: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000398: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003AC: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003C0: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003D4: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003E8: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003FC: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000410: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000424: 00000000 00 ..... BindingID = cfddcbc5-4411-48c3-8952-cc552b3eba76 FileIdProp = 1FileGroupId = 1 Size = 49280 MaxSize = 65535Growth = 128 Perf = 0 BackupLsn = (0:0:0)FirstUpdateLsn = (0:0:0) OldestRestoredLsn = (0:0:0) FirstNonloggedUpdateLsn = [NULL]MinSize = 384 Status = 0 UserShrinkSize = 65535SectorSize = 512 MaxLsn = (27:271:1) FirstLsn = (27:195:178)CreateLsn = (0:0:0) DifferentialBaseLsn = (878:877:46) DifferentialBaseGuid = 899c4a28-9429-46c1-92f4-f1e3c51d3490 FileOfflineLsn = (0:0:0)FileIdGuid = 76b65114-b1d9-4aa3-bcc0-185ae96fccb1 RestoreStatus = 8RestoreRedoStartLsn = (27:271:1) RestoreSourceGuid = 68d8496a-191b-464f-9a40-c068d8576519HardenedSkipLsn = [NULL] ReplTxfTruncationLsn = [NULL] TxfBackupLsn = [NULL]FstrContainerSize = [NULL] MaxLsnBranchId = 772ad053-3e87-4ec9-9792-6f64fe3febf8SecondaryRedoStartLsn = [NULL] SecondaryDifferentialBaseLsn = [NULL]ReadOnlyLsn = (0:0:0) ReadWriteLsn = (0:0:0) RestoreDifferentialBaseLsn = (27:195:178) RestoreDifferentialBaseGuid = 68d8496a-191b-464f-9a40-c068d8576519 RestorePathOriginhex (dec) = 0x00000000:00000000:0000 (0:0:0) m_guid = 00000000-0000-0000-0000-000000000000 DatabaseEncryptionFileState.m_maxScannedPage = 0 DatabaseEncryptionFileState.m_keyId = 0FCBFileDEKm_dbeStatusBits = 0 m_dtCreated = 1900-01-01 00:00:00.000m_dtLastRegenerated = 1900-01-01 00:00:00.000 m_dtLastModified = 1900-01-01 00:00:00.000 m_dtLastSet = 1900-01-01 00:00:00.000m_dtOpened = 1900-01-01 00:00:00.000m_algId = 0 m_algId = 0m_dwBitLen = 0 m_cbThumbprint = 0 m_rgbThumbprint = 0xDBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。
--看一下boot page的内容DBCC TRACEON(3604,-1)GODBCC PAGE([sss],1,9,3)GO
Page @0x00000002EA7DE000m_pageId = (1:9) m_headerVersion = 1 m_type = 13m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x200m_objId (AllocUnitId.idObj) = 99 m_indexId (AllocUnitId.idInd) = 0 Metadata: AllocUnitId = 6488064Metadata: PartitionId = 0 Metadata: IndexId = 0 Metadata: ObjectId = 99m_prevPage = (0:0) m_nextPage = (0:0) pminlen = 0m_slotCnt = 1 m_freeCnt = 6590 m_freeData = 1600m_reservedCnt = 0 m_lsn = (878:1345:2) m_xactReserved = 0m_xdesId = (0:0) m_ghostRecCnt = 0 m_tornBits = 2000067799DB Frag ID = 1 Allocation StatusGAM (1:2) = ALLOCATED SGAM (1:3) = NOT ALLOCATED PFS (1:1) = 0x64 MIXED_EXT ALLOCATED 100_PCT_FULL DIFF (1:6) = CHANGEDML (1:7) = NOT MIN_LOGGED Slot 0, Offset 0x60, Length 1504, DumpStyle BYTERecord Type = PRIMARY_RECORD Record Attributes = Record Size = 1504Memory Dump @0x000000000D1BA0600000000000000000: 0000e005 c2026302 00000000 00000000 00000000 ......c.............0000000000000014: 00000000 00000000 00000000 00000000 08008100 ....................0000000000000028: ae80847c bba19900 0ca30000 73007300 73002020 ...|........s.s.s. 000000000000003C: 20202020 20202020 20202020 20202020 20202020 0000000000000050: 20202020 20202020 20202020 20202020 20202020 0000000000000064: 20202020 20202020 20202020 20202020 20202020 0000000000000078: 20202020 20202020 20202020 20202020 20202020 000000000000008C: 20202020 20202020 20202020 20202020 20202020 00000000000000A0: 20202020 20202020 20202020 20202020 20202020 00000000000000B4: 20202020 20202020 20202020 20202020 20202020 00000000000000C8: 20202020 20202020 20202020 20202020 20202020 00000000000000DC: 20202020 20202020 20202020 20202020 20202020 00000000000000F0: 20202020 20202020 20202020 20202020 20202020 0000000000000104: 20202020 20202020 20202020 20202020 20202020 0000000000000118: 20202020 20202020 20202020 20202020 20202020 000000000000012C: 20202020 20202020 06000000 0a006e00 70170000 ......n.p...0000000000000140: 00000000 00000000 00000000 00000000 6e030000 ................n...0000000000000154: 6d030000 2e004000 6e030000 3a050000 0c000200 m.....@.n...:.......0000000000000168: 00000000 00000000 00000000 6e030000 3a050000 ............n...:...000000000000017C: 0c000000 c2271400 00000000 24d00000 00000000 .....'......$.......0000000000000190: 00000041 00000000 53d02a77 873ec94e 97926f64 ...A....S.*w.>.N..od00000000000001A4: fe3febf8 00e67dbf 00000000 00000000 00000000 .?....}.............00000000000001B8: 00000000 1b000000 0f010000 01000000 d305e86e ...................n00000000000001CC: 6e28d54a 892e8070 c5aec1fa 1b000000 0f010000 n(.J...p............00000000000001E0: 01000000 53d02a77 873ec94e 97926f64 fe3febf8 ....S.*w.>.N..od.?..00000000000001F4: 284a9c89 2994c146 92f4f1e3 c51d3490 14000000 (J..)..F......4.....0000000000000208: 01006302 00000000 00000000 00000000 22000000 ..c............."...000000000000021C: d0000000 03000400 80000000 00000000 00000000 ....................0000000000000230: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000244: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000258: 00000000 00000000 00000000 00000000 00000000 ....................000000000000026C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000280: c9020000 1e000000 e3000000 c3f9a100 bda30000 ....................0000000000000294: 00000000 00000000 00000000 00000000 553cda00 ................U<..00000000000002A8: 05a30000 b80b000b 00000000 59123e95 5d4a114b ............Y.>.]J.K00000000000002BC: b9a2abb7 5245120c 00000000 00000000 00000000 ....RE..............00000000000002D0: 00000000 00000000 00000000 00000000 96010000 ....................00000000000002E4: 00010000 00000000 00000000 00000000 02000000 ....................00000000000002F8: 00000000 00000000 00000000 00000000 00000000 ....................000000000000030C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000320: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000334: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000348: 00000000 00000000 00000000 00000000 00000000 ....................000000000000035C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000370: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000384: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000398: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003AC: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003C0: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003D4: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003E8: 00000000 00000000 00000000 00000000 00000000 ....................00000000000003FC: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000410: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000424: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000438: 00000000 00000000 00000000 00000000 00000000 ....................000000000000044C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000460: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000474: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000488: 00000000 00000000 00000000 00000000 00000000 ....................000000000000049C: 00000000 00000000 00000000 00000000 00000000 ....................00000000000004B0: 00000000 00000000 00000000 00000000 00000000 ....................00000000000004C4: 00000000 00000000 00000000 00000000 00000000 ....................00000000000004D8: 00000000 00000000 00000000 00000000 00000000 ....................00000000000004EC: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000500: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000514: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000528: 00000000 00000000 00000000 00000000 00000000 ....................000000000000053C: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000550: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000564: 00000000 00000000 00000000 00000000 00000000 ....................0000000000000578: 00000000 00000000 00000000 00000000 00000000 ....................000000000000058C: 00000000 00000000 00000000 00000000 00000000 ....................00000000000005A0: 00000000 00000000 00000000 20000000 78000000 ............ ...x...00000000000005B4: 43000000 00000000 00000000 00000000 00000000 C...................00000000000005C8: 00000000 00000000 00000000 00000000 00000000 ....................00000000000005DC: 00000000 .... DBINFO @0x000000000D1BA060dbi_version = 706 dbi_createVersion = 611 dbi_SEVersion = 0dbi_dvSplitPoint = 0:0:0 (0x00000000:00000000:0000) dbi_dbbackupLSN = 0:0:0 (0x00000000:00000000:0000) dbi_LastLogBackupTime = 1900-01-01 00:00:00.000 dbi_nextseqnum = 1900-01-01 00:00:00.000 dbi_status = 0x00810008dbi_crdate = 2014-04-13 09:19:21.370dbi_dbname = sss dbi_dbid = 10dbi_cmptlevel = 110 dbi_masterfixups = 0 dbi_maxDbTimestamp = 6000dbi_dbbackupLSN = 0:0:0 (0x00000000:00000000:0000) dbi_RebuildLogs = 0dbi_differentialBaseLSN = 878:877:46 (0x0000036e:0000036d:002e) dbi_RestoreFlags = 0x0040dbi_checkptLSN = 878:1338:12 (0x0000036e:0000053a:000c) dbi_dbccFlags = 2dbi_COWLastLSN = 0:0:0 (0x00000000:00000000:0000) dbi_DirtyPageLSN = 878:1338:12 (0x0000036e:0000053a:000c) dbi_RecoveryFlags = 0x00000000dbi_lastxact = 0x1427c2 dbi_collation = 53284 dbi_relstat = 0x41000000dbi_familyGUID = 772ad053-3e87-4ec9-9792-6f64fe3febf8 dbi_maxLogSpaceUsed = 3212699136dbi_recoveryForkNameStackentry 0hex (dec) = 0x0000001b:0000010f:0001 (27:271:1) m_guid = 6ee805d3-286e-4ad5-892e-8070c5aec1fa entry 1hex (dec) = 0x0000001b:0000010f:0001 (27:271:1) m_guid = 772ad053-3e87-4ec9-9792-6f64fe3febf8 dbi_differentialBaseGuid = 899c4a28-9429-46c1-92f4-f1e3c51d3490 dbi_firstSysIndexes = 0001:00000014dbi_oldestBackupXactLSN = 0:0:0 (0x00000000:00000000:0000) dbi_versionChangeLSN = 34:208:3 (0x00000022:000000d0:0003) dbi_mdUpgStat = 0x0004dbi_category = 0x0000000000000080 dbi_safetySequence = 0 dbi_dbMirrorId = 00000000-0000-0000-0000-000000000000 dbi_pageUndoLsn = 0:0:0 (0x00000000:00000000:0000) dbi_pageUndoState = 0dbi_disabledSequence = 0 dbi_dbmRedoLsn = 0:0:0 (0x00000000:00000000:0000)dbi_dbmOldestXactLsn = 0:0:0 (0x00000000:00000000:0000) dbi_CloneCpuCount = 0dbi_CloneMemorySize = 0 dbi_updSysCatalog = 1900-01-01 00:00:00.000dbi_LogBackupChainOrigin = 713:30:227 (0x000002c9:0000001e:00e3) dbi_dbccLastKnownGood = 2014-10-07 09:49:44.117 dbi_roleSequence = 0dbi_dbmHardenedLsn = 0:0:0 (0x00000000:00000000:0000) dbi_localState = 0dbi_safety = 0 dbi_modDate = 2014-04-06 13:14:34.310dbi_verRDB = 184552376 dbi_lazyCommitOption = 0 dbi_svcBrokerGUID = 953e1259-4a5d-4b11-b9a2-abb75245120c dbi_svcBrokerOptions = 0x00000000dbi_dbmLogZeroOutstanding = 0 dbi_dbmLastGoodRoleSequence = 0 dbi_dbmRedoQueue = 0dbi_dbmRedoQueueType = 0 dbi_rmidRegistryValueDeleted = 0 dbi_dbmConnectionTimeout = 0dbi_fragmentId = 0 dbi_AuIdNext = 1099511628182 dbi_MinSkipLsn = 0:0:0 (0x00000000:00000000:0000) dbi_commitTsOfcheckptLSN = 2dbi_dbEmptyVersionState = 0 dbi_CurrentGeneration = 0 dbi_EncryptionHistoryScan 0hex (dec) = 0x00000000:00000000:0000 (0:0:0) EncryptionScanInfo:ScanId = 0 Scan 1hex (dec) = 0x00000000:00000000:0000 (0:0:0) EncryptionScanInfo:ScanId = 0 Scan 2hex (dec) = 0x00000000:00000000:0000 (0:0:0) EncryptionScanInfo:ScanId = 0 dbi_latestVersioningUpgradeLSN = 32:120:67 (0x00000020:00000078:0043) dbi_splitAGE = 0dbi_PendingRestoreOutcomesId = 00000000-0000-0000-0000-000000000000 dbi_ContianmentState = 0
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