Sunday, January 4, 2015

Script to find the Fragmentation of indexes

Below is the script to find the fragmentation of the indexes created on a database.

SELECT OBJECT_NAME(OBJECT_ID), index_id,index_type_desc,index_level,
avg_fragmentation_in_percent,avg_page_space_used_in_percent,page_count
FROM sys.dm_db_index_physical_stats (DB_ID( N'Database name') , NULL, NULL, NULL , 'SAMPLED') ORDER BY avg_fragmentation_in_percent DESC

avg_fragmentation_in_percent represents  logical fragmentation.

If this value is higher than 5% and less than 30%, then we should use 

ALTER INDEXREORGANIZE

If this value is higher than 30%, then we should use 

ALTER INDEX REBUILD WITH (ONLINE = ON)

Please note:- As per MSDN, rebuilding an index can be executed online or offline. Reorganizing an index is always executed online. To achieve availability similar to the reorganize option, you should rebuild indexes online.

Read more about Fragmentation

Read more about Indexes

Read more about Reorganize and Rebuild Indexes



3 comments:

  1. OBJECT_NAME() will be scoped to the current database, which is master in your example, despite the OBJECT_ID being from another database, so that could return nothing or name of an object from the master database if one exists with the same OBJECT_ID. Also, online index rebuilds are only available in Enterprise (or Developer) edition, so many people can't use that feature.

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  2. Thanks For Correction. I have remove the Use Master command.:-)

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  3. script that works (subst function: do yourself).

    What I do NOT understand: there are some tables I reorganize over and over again, but fragmentation stays high, up to 66 %.

    alter procedure _adm_reorg_ix
    as
    /*
    if @@error = 0
    exec _adm_reorg_ix
    */

    declare @c cursor
    set @c = cursor for
    select sql from ( -- a
    SELECT
    tab_name= o.name,
    ind_name = i.name,
    avg_fragmentation_in_percent,
    page_count,
    sql = case
    when avg_fragmentation_in_percent < 5 then
    ''
    when avg_fragmentation_in_percent < 30 and page_count > 100 then
    dbo.subst2('ALTER INDEX $1 on $2 reorganize',i.name,o.name) collate database_default
    else
    dbo.subst2('ALTER INDEX $1 on $2 rebuild WITH (ONLINE = OFF)',i.name,o.name) collate database_default
    end,
    s.index_id,
    s.index_type_desc,
    s.index_level,
    avg_page_space_used_in_percent
    FROM
    master.sys.dm_db_index_physical_stats (DB_ID(db_name()) , NULL, NULL, NULL , 'SAMPLED') s
    left join sys.indexes i on i.object_id = s.object_id and i.index_id = s.index_id
    cross apply ( values (OBJECT_NAME(s.OBJECT_ID))) o (name)
    --order by 3 desc
    ) a
    where sql <> ''

    declare @sql varchar(300)
    open @c
    while 0= 0 begin
    fetch next from @c into @sql
    if @@fetch_status <> 0 break
    print @sql
    exec (@sql)
    end
    go

    ReplyDelete