SQLSERVER中的鬼影索引

SQLSERVER中的鬼影索引

看这篇文章之前可以先看一下鬼影记录

了解了解一下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，当提交事务的时候才真正删除索引记录，

或者回滚事务，鬼影索引记录才会恢复为正常索引记录，这样做的目的就是提高了性能

鬼影索引只会出现在非聚集索引页，聚集索引页是没有鬼影索引的

---

建立环境

 --ghost index record
 USE [pratice]
 GO
 --建表
 CREATE TABLE testghostindexnoncluster(id INT IDENTITY(1,1),NAME VARCHAR(20))
 GO
 --插入记录
 INSERT INTO testghostindexnoncluster(name)
 SELECT '' UNION ALL
 SELECT ''
 GO

 CREATE  INDEX IX_testghostindexnoncluster ON testghostindexnoncluster([Id] ASC)

 SELECT * FROM [dbo].[testghostindexnoncluster]
 GO

 --TRUNCATE TABLE DBCCResult
 INSERT INTO DBCCResult EXEC ('DBCC IND(pratice,testghostindexnoncluster,-1) ')

 SELECT * FROM [dbo].[DBCCResult] ORDER BY [PageType] DESC 

 DBCC TRACEON(3604,-1)
 GO
 DBCC PAGE([pratice],1,15663,1)  --索引页
 GO

正常情况下的索引页面,Record Type = INDEX_RECORD

 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: (1:15663)

 BUFFER:

 BUF @0x03E53304

 bpage = 0x1A468000                   bhash = 0x00000000                   bpageno = (1:15663)
 bdbid = 5                            breferences = 0                      bUse1 = 7847
 bstat = 0xc0000b                     blog = 0x1212121b                    bnext = 0x00000000

 PAGE HEADER:

 Page @0x1A468000

 m_pageId = (1:15663)                 m_headerVersion = 1                  m_type = 2
 m_typeFlagBits = 0x0                 m_level = 0                          m_flagBits = 0x4000
 m_objId (AllocUnitId.idObj) = 539    m_indexId (AllocUnitId.idInd) = 256
 Metadata: AllocUnitId = 72057594073251840
 Metadata: PartitionId = 72057594061062144                                 Metadata: IndexId = 2
 Metadata: ObjectId = 1463676262      m_prevPage = (0:0)                   m_nextPage = (0:0)
 pminlen = 13                         m_slotCnt = 2                        m_freeCnt = 8066
 m_freeData = 135                     m_reservedCnt = 0                    m_lsn = (3046:350:12)
 m_xactReserved = 0                   m_xdesId = (0:11665608)              m_ghostRecCnt = 0
 m_tornBits = 0                       

 Allocation Status

 GAM (1:2) = ALLOCATED                SGAM (1:3) = ALLOCATED
 PFS (1:8088) = 0x60 MIXED_EXT ALLOCATED   0_PCT_FULL                      DIFF (1:6) = CHANGED
 ML (1:7) = NOT MIN_LOGGED            

 DATA:

 Slot 0, Offset 0x7a, Length 13, DumpStyle BYTE

 Record Type = INDEX_RECORD           Record Attributes =
 Memory Dump @0x0849C07A

 00000000:   06010000 00b52000 00010000 00††††††††...... ......            

 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE

 Record Type = INDEX_RECORD           Record Attributes =
 Memory Dump @0x0849C06D

 00000000:   06020000 00b52000 00010001 00††††††††...... ......            

 OFFSET TABLE:

 Row - Offset
 1 (0x1) - 109 (0x6d)
 0 (0x0) - 122 (0x7a)                 

 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

 SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
 GO
 BEGIN TRAN
 DELETE FROM  testghostindexnoncluster WHERE [id]=1
 --ROLLBACK TRAN

再看一下索引页面

 DBCC TRACEON(3604,-1)
 GO
 DBCC PAGE([pratice],1,15663,1)  --索引页
 GO

 DATA:

 Slot 0, Offset 0x7a, Length 13, DumpStyle BYTE

 Record Type = GHOST_INDEX_RECORD     Record Attributes =
 Memory Dump @0x0849C07A

 00000000:   0a010000 00b52000 00010000 00††††††††...... ......            

 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE

 Record Type = INDEX_RECORD           Record Attributes =
 Memory Dump @0x0849C06D

 00000000:   06020000 00b52000 00010001 00††††††††...... ......            

 OFFSET TABLE:

 Row - Offset
 1 (0x1) - 109 (0x6d)
 0 (0x0) - 122 (0x7a)                 

 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

 ROLLBACK TRAN

恢复正常了，索引页面中第一行记录的Record Type = INDEX_RECORD

 DATA:

 Slot 0, Offset 0x94, Length 13, DumpStyle BYTE

 Record Type = INDEX_RECORD           Record Attributes =
 Memory Dump @0x0849C094

 00000000:   06010000 00b52000 00010000 00††††††††...... ......            

 Slot 1, Offset 0x6d, Length 13, DumpStyle BYTE

 Record Type = INDEX_RECORD           Record Attributes =
 Memory Dump @0x0849C06D

 00000000:   06020000 00b52000 00010001 00††††††††...... ......            

 OFFSET TABLE:

 Row - Offset
 1 (0x1) - 109 (0x6d)
 0 (0x0) - 148 (0x94)                 

 DBCC 执行完毕。如果 DBCC 输出了错误信息，请与系统管理员联系。

 DROP TABLE testghostindexnoncluster
 GO

如有不对的地方，欢迎大家拍砖o(∩_∩)o