SQL Server中的鬼影记录
SQL Server中的鬼影记录
看这篇文章之前可以先查看下面文章先了解鬼影记录
了解一下SQLSERVER里的鬼影记录
关于鬼影记录的翻译一
关于鬼影记录的翻译二
当删除表中的某一条记录的时候，索引页面的对应记录并不是马上删除，而是标记为鬼影，即使提交事务也不会立刻删除索引记录，
当回滚事务时候，鬼影记录也会恢复为正常索引记录，这样做的目的就是提高了性能，后面后台鬼影清理进程会慢慢把鬼影记录物理删除
鬼影记录说明了一个道理，数据库并不会真正物理删除一条记录entry，只会逻辑删除或者软删除，提高性能
建立环境
1 --ghost index record 2 USE [pratice] 3 GO 4 --建表 5 CREATE TABLE testghostindexnoncluster(id INT IDENTITY(1,1),NAME VARCHAR(20)) 6 GO 7 --插入记录 8 INSERT INTO testghostindexnoncluster(name) 9 SELECT '1' UNION ALL 10 SELECT '2' 11 GO 12 13 CREATE INDEX IX_testghostindexnoncluster ON testghostindexnoncluster([Id] ASC) 14 15 SELECT * FROM [dbo].[testghostindexnoncluster] 16 GO
1 --TRUNCATE TABLE DBCCResult 2 INSERT INTO DBCCResult EXEC ('DBCC IND(pratice,testghostindexnoncluster,-1) ') 3 4 SELECT * FROM [dbo].[DBCCResult] ORDER BY [PageType] DESC 5 6 DBCC TRACEON(3604,-1) 7 GO 8 DBCC PAGE([pratice],1,15663,1) --索引页 9 GO
正常情况下的索引页面,Record Type = INDEX_RECORD
1 DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。 2 3 PAGE: (1:15663) 4 5 6 BUFFER: 7 8 9 BUF @0x03E53304 10 11 bpage = 0x1A468000 bhash = 0x00000000 bpageno = (1:15663) 12 bdbid = 5 breferences = 0 bUse1 = 7847 13 bstat = 0xc0000b blog = 0x1212121b bnext = 0x00000000 14 15 PAGE HEADER: 16 17 18 Page @0x1A468000 19 20 m_pageId = (1:15663) m_headerVersion = 1 m_type = 2 21 m_typeFlagBits = 0x0 m_level = 0 m_flagBits = 0x4000 22 m_objId (AllocUnitId.idObj) = 539 m_indexId (AllocUnitId.idInd) = 256 23 Metadata: AllocUnitId = 72057594073251840 24 Metadata: PartitionId = 72057594061062144 Metadata: IndexId = 2 25 Metadata: ObjectId = 1463676262 m_prevPage = (0:0) m_nextPage = (0:0) 26 pminlen = 13 m_slotCnt = 2 m_freeCnt = 8066 27 m_freeData = 135 m_reservedCnt = 0 m_lsn = (3046:350:12) 28 m_xactReserved = 0 m_xdesId = (0:11665608) m_ghostRecCnt = 0 29 m_tornBits = 0 30 31 Allocation Status 32 33 GAM (1:2) = ALLOCATED SGAM (1:3) = ALLOCATED 34 PFS (1:8088) = 0x60 MIXED_EXT ALLOCATED 0_PCT_FULL DIFF (1:6) = CHANGED 35 ML (1:7) = NOT MIN_LOGGED 36 37 DATA: 38 39 40 Slot 0, Offset 0x7a, Length 13, DumpStyle BYTE 41 42 Record Type = INDEX_RECORD Record Attributes = 43 Memory Dump @0x0849C07A 44 45 00000000: 06010000 00b52000 00010000 00††††††††...... ...... 46 47 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE 48 49 Record Type = INDEX_RECORD Record Attributes = 50 Memory Dump @0x0849C06D 51 52 00000000: 06020000 00b52000 00010001 00††††††††...... ...... 53 54 OFFSET TABLE: 55 56 Row - Offset 57 1 (0x1) - 109 (0x6d) 58 0 (0x0) - 122 (0x7a) 59 60 61 DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。
我们删除id=1的记录
1 SET TRANSACTION ISOLATION LEVEL REPEATABLE READ 2 GO 3 BEGIN TRAN 4 DELETE FROM testghostindexnoncluster WHERE [id]=1 5 --ROLLBACK TRAN
再看一下索引页面
1 DBCC TRACEON(3604,-1) 2 GO 3 DBCC PAGE([pratice],1,15663,1) --索引页 4 GO
1 DATA: 2 3 4 Slot 0, Offset 0x7a, Length 13, DumpStyle BYTE 5 6 Record Type = GHOST_INDEX_RECORD Record Attributes = 7 Memory Dump @0x0849C07A 8 9 00000000: 0a010000 00b52000 00010000 00††††††††...... ...... 10 11 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE 12 13 Record Type = INDEX_RECORD Record Attributes = 14 Memory Dump @0x0849C06D 15 16 00000000: 06020000 00b52000 00010001 00††††††††...... ...... 17 18 OFFSET TABLE: 19 20 Row - Offset 21 1 (0x1) - 109 (0x6d) 22 0 (0x0) - 122 (0x7a) 23 24 25 DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。
可以看到第一行记录被标记为Record Type = GHOST_INDEX_RECORD
我们回滚事务
1 ROLLBACK TRAN
恢复正常了，索引页面中第一行记录的Record Type = INDEX_RECORD
1 DATA: 2 3 4 Slot 0, Offset 0x94, Length 13, DumpStyle BYTE 5 6 Record Type = INDEX_RECORD Record Attributes = 7 Memory Dump @0x0849C094 8 9 00000000: 06010000 00b52000 00010000 00††††††††...... ...... 10 11 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE 12 13 Record Type = INDEX_RECORD Record Attributes = 14 Memory Dump @0x0849C06D 15 16 00000000: 06020000 00b52000 00010001 00††††††††...... ...... 17 18 OFFSET TABLE: 19 20 Row - Offset 21 1 (0x1) - 109 (0x6d) 22 0 (0x0) - 148 (0x94) 23 24 25 DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。
1 DROP TABLE testghostindexnoncluster 2 GO
如有不对的地方，欢迎大家拍砖o(∩_∩)o
