[转]SQL SERVER整理索引碎片测试

2022-08-14 08:34:03

SQL SERVER整理索引碎片测试

SQL SERVER整理索引的方法也就这么几种，而且老是自作聪明的加入智能判断很不爽，还是比DBMS_ADVISOR差远了：

1SQL SERVER 2000/2005

查询

2000
use DB_Name
declare @table_id int
set @table_id=object_id('Table_Name')
dbcc showcontig(@table_id)

2005
SELECT index_id,index_type_desc,avg_fragmentation_in_percent,page_count
FROM sys.dm_db_index_physical_stats(db_id(), OBJECT_ID('Table_Name'), NULL, NULL , 'LIMITED');

整理

2000
DBCC INDEXDEFRAG (DB_Name, 'dbo.Table_Name', Index_Name)
DBCC DBREINDEX ('DB_Name.dbo.Table_Name','',100)

2005
ALTER INDEX Index_Name ON dbo.Table_Name REBUILD

以下是一个网上找的不错的例子，链接是：
http://www.cnblogs.com/perfectdesign/archive/2008/02/20/sqlserverreindexrebuild.html
新建一个表：

create table t3

(

i int primary key,

xx varchar(200) not null

)

加入数据：

declare @x int

set @x = 0

while @x <1000

begin

insert into t3 values (@x,'qweasdqweasdqweasdqweqweasdqwe')

set @x = @x+1

end

执行动态管理视图：

SELECT index_id,index_type_desc,avg_fragmentation_in_percent,page_count
FROM sys.dm_db_index_physical_stats
(db_id(), OBJECT_ID('t3'), NULL, NULL , 'LIMITED');

可以看到：

index_id为0表示这个是堆，平均的碎片有33%

现在执行几个可以减少碎片的方法都不管用，不能减少碎片。
包括：

DBCC INDEXDEFRAG (test, 'dbo.t3', PK__t3__0EA330E9)

alter index PK__t3__0EA330E9 on t3

rebuild

dbcc dbreindex ('t3')

这几个方法还有删除重建索引，都不能减少碎片数量。

后来我觉得是因为数据太少了，导致页也很少，数据库可能存在某种智能，判断是否值得去做重建索引的工作，所以加大的数据量：

declare @x int

set @x = 1000

while @x <10000

begin

insert into t3 values (@x,'qweasdqweasdqweasdqweqweasdqwe')

set @x = @x+1

end

再执行语句：

SELECT index_id,index_type_desc,avg_fragmentation_in_percent,page_count
FROM sys.dm_db_index_physical_stats
(db_id(), OBJECT_ID('t3'), NULL, NULL , 'LIMITED');

alter index t3index on t3 rebuild

显示出来了！

结论：
SQL Server在执行相关的操作的时候都会智能去判断是否值得去做，比如在页面数太小的情况下可以不去重建索引，rebuild reindex 。类似的，在SQL Server 2005 里面也多了许多智能的判断来保证一个完整庞大而又不失智能的设计，
比如：
生成查询计划的阀值
缓存机制，缓存的筛选，LRU算法
预读机制
checkpoint减少回滚距离
智能join判断
重编译

了解SQL Server这种类似的软件产品能够为我们在设计产品的时候提供更多的思路想法，即使你了解上面的东西对你的SQL开发也不会有太多帮助。

另外附上几种方式的区别：
reindex是比较好的选择，速度快，但是他不能在线操作
INDEXDEFRAG 比较慢，但是可以在线操作
rebuild建议在碎片较少时采用。

附上微软的重建索引脚本，从里面也可以看出微软根据碎片大小推荐的方式，不过这个要随每个不同的数据库而定。

-- ensure a USE <databasename> statement has been executed first.

SET NOCOUNT ON;

DECLARE @objectid int;

DECLARE @indexid int;

DECLARE @partitioncount bigint;

DECLARE @schemaname sysname;

DECLARE @objectname sysname;

DECLARE @indexname sysname;

DECLARE @partitionnum bigint;

DECLARE @partitions bigint;

DECLARE @frag float;

DECLARE @command varchar(8000);

-- ensure the temporary table does not exist

IF EXISTS (SELECT name FROM sys.objects WHERE name = 'work_to_do')

DROP TABLE work_to_do;

-- conditionally select from the function, converting object and index IDs to names.

SELECT

object_id AS objectid,

index_id AS indexid,

partition_number AS partitionnum,

avg_fragmentation_in_percent AS frag

INTO work_to_do

FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL , NULL, 'LIMITED')

WHERE avg_fragmentation_in_percent > 10.0 AND index_id > 0;

-- Declare the cursor for the list of partitions to be processed.

DECLARE partitions CURSOR FOR SELECT * FROM work_to_do;

-- Open the cursor.

OPEN partitions;

-- Loop through the partitions.

FETCH NEXT

FROM partitions

INTO @objectid, @indexid, @partitionnum, @frag;

WHILE @@FETCH_STATUS = 0

BEGIN;

SELECT @objectname = o.name, @schemaname = s.name

FROM sys.objects AS o

JOIN sys.schemas as s ON s.schema_id = o.schema_id

WHERE o.object_id = @objectid;

SELECT @indexname = name

FROM sys.indexes

WHERE object_id = @objectid AND index_id = @indexid;

SELECT @partitioncount = count (*)

FROM sys.partitions

WHERE object_id = @objectid AND index_id = @indexid;

-- 30 is an arbitrary decision point at which to switch between reorganizing and rebuilding

IF @frag < 30.0

BEGIN;

SELECT @command = 'ALTER INDEX ' + @indexname + ' ON ' + @schemaname + '.' + @objectname + ' REORGANIZE';

IF @partitioncount > 1

SELECT @command = @command + ' PARTITION=' + CONVERT (CHAR, @partitionnum);

EXEC (@command);

END;

IF @frag >= 30.0

BEGIN;

SELECT @command = 'ALTER INDEX ' + @indexname +' ON ' + @schemaname + '.' + @objectname + ' REBUILD';

IF @partitioncount > 1

SELECT @command = @command + ' PARTITION=' + CONVERT (CHAR, @partitionnum);

EXEC (@command);

END;

PRINT 'Executed ' + @command;

FETCH NEXT FROM partitions INTO @objectid, @indexid, @partitionnum, @frag;

END;

-- Close and deallocate the cursor.

CLOSE partitions;

DEALLOCATE partitions;

-- drop the temporary table

IF EXISTS (SELECT name FROM sys.objects WHERE name = 'work_to_do')

DROP TABLE work_to_do;

BOL的推荐：

avg_fragmentation_in_percent 值	修复语句
> 5% 且 < = 30%	ALTER INDEX REORGANIZE
> 30%	ALTER INDEX REBUILD WITH (ONLINE = ON)*

小于5没必要重建，所以上面的SQL语句还是有得商量的地方。

http://blog.csdn.net/greenery/archive/2008/08/06/2778486.aspx

/************************************** 作用:在线整理索引碎片时间:2008-5-15 说明：根据微软的示例改编适用于无法停机重建索引的情况，在线整理索引碎片，并更新表的统计信息以增强效果。另外可以自定义需要整理的索引的逻辑碎片程度，扫描密度，页数必须要在数据库访问较少的时候执行 ***************************************/ CREATE PROC [dbo].[SYS_IndexDrag] AS BEGIN

SET NOCOUNT ON
DECLARE @tablename VARCHAR (128)
DECLARE @execstr VARCHAR (255)
DECLARE @objectid INT
DECLARE @indexid INT
DECLARE @frag DECIMAL
DECLARE @maxfrag DECIMAL--逻辑碎片

DECLARE @MaxScanDensity DECIMAL--扫描密度

DECLARE @Page INT --8k页数,设定一个限度对一定大的索引进行整理

DECLARE @TmpName VARCHAR(150)

-- Decide on the maximum fragmentation to allow

SELECT @maxfrag = 30.0
SELECT @MaxScanDensity=70.0
SELECT @Page=400

-- Declare cursor

DECLARE tables CURSOR FOR
   SELECT TABLE_NAME
   FROM INFORMATION_SCHEMA.TABLES
   WHERE TABLE_TYPE = 'BASE TABLE'

-- Create the table

CREATE TABLE #fraglist (
   ObjectName CHAR (255),
   ObjectId INT,
   IndexName CHAR (255),
   IndexId INT,
   Lvl INT,
   CountPages INT,
   CountRows INT,
   MinRecSize INT,
   MaxRecSize INT,
   AvgRecSize INT,
   ForRecCount INT,
   Extents INT,
   ExtentSwitches INT,
   AvgFreeBytes INT,
   AvgPageDensity INT,
   ScanDensity DECIMAL,
   BestCount INT,
   ActualCount INT,
   LogicalFrag DECIMAL,
   ExtentFrag DECIMAL)

-- Open the cursor

OPEN tables

-- Loop through all the tables in the database

FETCH NEXT
FROM tables
INTO @tablename

WHILE @@FETCH_STATUS = 0
BEGIN
-- Do the showcontig of all indexes of the table

INSERT INTO #fraglist
   EXEC ('DBCC SHOWCONTIG (''' + @tablename + ''')
      WITH FAST, TABLERESULTS, ALL_INDEXES, NO_INFOMSGS')

   FETCH NEXT
      FROM tables
      INTO @tablename
END

-- Close and deallocate the cursor

CLOSE tables
DEALLOCATE tables

-- Declare cursor for list of indexes to be defragged

DECLARE indexes CURSOR FOR
   SELECT ObjectName, ObjectId, IndexId, LogicalFrag
   FROM #fraglist
   WHERE (LogicalFrag >= @maxfrag OR [ScanDensity]<=@MaxScanDensity) AND [CountPages]>=@page
      AND INDEXPROPERTY (ObjectId, IndexName, 'IndexDepth') > 0

-- Open the cursor

OPEN indexes

-- loop through the indexes

FETCH NEXT
FROM indexes
INTO @tablename, @objectid, @indexid, @frag

WHILE @@FETCH_STATUS = 0
BEGIN

--在线整理碎片

PRINT 'Executing DBCC INDEXDEFRAG (0, ' + RTRIM(@tablename) + ',
      ' + RTRIM(@indexid) + ') - fragmentation currently '
       + RTRIM(CONVERT(varchar(15),@frag)) + '%'
   SELECT @execstr = 'DBCC INDEXDEFRAG (0, ' + RTRIM(@objectid) + ',
       ' + RTRIM(@indexid) + ')'
   EXEC (@execstr)

   --更新统计信息

IF @TmpName<>@tablename
   BEGIN
        SET @tmpName=@tableName
        EXEC('UPDATE STATISTICS '+@TableName)
   END

   FETCH NEXT
      FROM indexes
      INTO @tablename, @objectid, @indexid, @frag
END

-- Close and deallocate the cursor

CLOSE indexes
DEALLOCATE indexes

-- Delete the temporary table

DROP TABLE #fraglist

END

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