PK Still Shows Fragmentation After ALTER INDEX.. REBUILD
Sep 4, 2007
I am using sys.dm_db_index_physical_stats to identify indexes that need to be rebuilt based on a fragmentation limit. Once identified, I execute and ALTER INDEX... REBUILD on the index. If the index is clustered, only that index gets rebuilt for the table. After all the indexes are complete, I receive a report on the indexes that were rebuilt in the databases and what level of fragmentation the index was at before rebuilt. After checking these indexes, I still see that all the Primary Key indexes are still at the same fragmentation level. I run the process again and it does not change. I updated table usage and also ran update statistics after running the rebuild again, but the fragmentation does not change. Why can€™t these PK Clustered indexes be rebuilt as expected? Do I need to drop and recreate the PK before this fragmentation changes?
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Apr 23, 2007
I have been testing methods to maintain indexes in a SQL Server 2005 database which has been migrated from SQL Server 2000. The compatibility level is still set to 80. I used the query below to inspect the degree of fragmentation amongst other things.
SELECT a.index_id
, name
, database_id
, avg_fragmentation_in_percent
,index_type_desc
,fragment_count
,page_count
FROM sys.dm_db_index_physical_stats (NULL, NULL, NULL, NULL, 'DETAILED') AS a
JOIN sys.indexes AS b ON a.object_id = b.object_id AND a.index_id = b.index_id
Some of the indexes in the database had a high degree of fragmentation based on the avg_fragmentation_in_percent value. I tried drop+create, rebuild and reorganise commands on those indexes. Predictably, drop + create was the most effective, but even that did not always reduce fragmentation much. Sometimes the fragmentation was the same no matter what method I used. Other times drop+create helped, rebuild made it worse.
What is going on?
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Mar 10, 2007
I thought I would delve into index fragmentation and I found somegreat sql from many posters (thanks Erland!).My question is how bad is bad? I know this is very subjective.Some scripts I found would reindex if the LogicalFragmenation is over30%.I have some tables that are 98% (I'm guessing really bad). I know itall depends..more as a learning point: I found a table that had over 30%logicalfragmentation, I dropped the indexes, created then ran thescript that used type code segment:'DBCC SHOWCONTIG(' + @TableName + ') WITH TABLERESULTS, ALL_INDEXES,NO_INFOMSGS')In one case, the indexes for the table dropped below 30%, in anothercase the index was still fragmented ever after I dropped and re-created index.SQL Server 2005 x64 SP2This is the script I am running (I found this in another thread thatErland posted):SET NOCOUNT ONUSE ds_v6_sourceDECLARE @TableName VARCHAR(100)-- Create a table to hold the results of DBCC SHOWCONTIGIF OBJECT_ID('Tempdb.dbo.#Contig') IS NOT NULLDROP TABLE #ContigCREATE TABLE #Contig ([ObjectName] VARCHAR(100), [ObjectId] INT,[IndexName]VARCHAR(200),[IndexId] INT, [Level] INT, [Pages] INT , [Rows] INT ,[MinimumRecordSize] INT,[MaximumRecordSize] INT , [AverageRecordSize] INT,[ForwardedRecords] INT ,[Extents] INT, [ExtentSwitches] INT, [AverageFreeBytes]NUMERIC(6,2),[AveragePageDensity] NUMERIC(6,2), [ScanDensity]NUMERIC(6,2) ,[BestCount] INT ,[ActualCount] INT , [LogicalFragmentation] NUMERIC(6,2) ,[ExtentFragmentation] NUMERIC(6,2) )DECLARE curTables CURSOR STATIC LOCALFORSELECT Table_NameFROM Information_Schema.TablesWHERE Table_Type = 'BASE TABLE'OPEN curTablesFETCH NEXT FROM curTables INTO @TableNameSET @TableName = RTRIM(@TableName)WHILE @@FETCH_STATUS = 0BEGININSERT INTO #Contig EXEC('DBCC SHOWCONTIG(' + @TableName + ') WITHTABLERESULTS, ALL_INDEXES, NO_INFOMSGS')FETCH NEXT FROM curTables INTO @TableNameENDCLOSE curTablesDEALLOCATE curTables
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May 1, 2008
If the index to be rebuilt is a clustered index, will all non-clustered indexes be rebuilt also by rebuilding only the clustered index.
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Nov 16, 2007
Does "Alter Index All Rebuild" rebuild just the tree level of the index? Or does it also rebuild the leaf level like reorganize?
Thanks and God Bless,
Thomas
ThomBeaux
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Aug 30, 2007
I have read through BOL but am still confused by the above sql. I think it rebuilds all indexes on a table. Am I correct? (If so, if would seem to be a good thing to run it nightly on all tables in all databases. Or maybe that is too extreme)
Barkingdog
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Jul 9, 2007
I do a lot of index maintenance and started testing rebuilding my indexes with the ONLINE option, but noticed an increase in record size by 14 bytes. The issue I have is that for each index you build the ONLINE option, you add 14 bytes for row. After the index rebuild is done, normal transaction updates drop the additional 14 bytes.
The act of adding and dropping 14 bytes would cause fragmentation and uncompressed data. Is this correct or do I have something wrong?
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May 20, 2015
I'm working on re-indexing a table using some commands from ALTER INDEX REBUILD from Microsoft. The indexes will be tested for threshold fragmentation. my plan is once the reindex is executed, a transaction backup will occur while controlling the size of the log file. Â The query impose time limitations or stop reindexing after the specified amount of time has elapsed.
my question,
1. How can I integrate a query which checks if transaction log is getting full and which runs a Tlog backup if over 70%
2. How do I impose time limitation?
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Oct 28, 2015
My SSIS package is running very slow taking so much time to execute, One task is taking 2hr for inserting 100k records, i have disabled unused index still it is taking time.I am rebuilding/Refreshing indexes and stats once in month if i try to execute on daily basis will it improve my SSIS Package performance?Â
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Jun 22, 2008
What functions of tools do you use for managing index fragmentation?
DBCC?
I am working through MS Press SQL 2005 book and it mentions the
sys.dm_db_index_physical_stats function? It then give an example of code which is very involved.
Does anybody use this function?
Thanks
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May 10, 2007
before rebuild index
---------------------
tablenameIndexname
avg_fragmentation_in_percent
Payoff_QuotePK_Payoff_QuoteDetail
83.3333333333333
ALTER INDEX ALL ON Payoff_Quote REBUILD
after issue the above statement result remain same.
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Jun 24, 2007
Hi
When I run sys.dm_db_index_physical_stats on AdventureWorks.Production.Product, I get an average fragmentaion of 46%, 0%, 25% & 50% on the Indexes.
I run ALTER INDEX ALL ON AdventureWorks.Production.Product
REBUILD WITH (FILLFACTOR = 80, SORT_IN_TEMPDB = ON,
STATISTICS_NORECOMPUTE = ON)
and the index fragmentation does not change...
Why is that?? I have tried refreshing the table and the statistics but why does it look like rebuilding the indexes has done nothing?
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Sep 25, 2007
I have a nice script that will look at the index fragmentation by using the DMV (sys.dm_db_index_physical_stats) and if its above a specificed threshhold, it will rebuild or reorg the index.
What I have noticed is that even after reorging and/or rebuilding the index, the fragmentation percent in the DMV does not change for some indexes. Other indexes are updated just fine.
Is this a result of updating statistics? Why would the fragmentation change for some indexes and not others? Why does it seem no matter how much rebuilding or reorging is done, the fragmentation percent for some indexes does not change?
- Eric
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May 11, 2015
We have nightly job running to reorg all in one of our prod database. But the index on one of the table fragmenting quickly by the morning showing 90% fragmentation.
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Feb 9, 2008
Hi,
It is natural that index gets fragment overtime. But I would like to know how you do the reindexing or defragment when your database table is big and you cannot afford the time to rebuild them. Thanks.
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Nov 8, 2007
I have several databases in which our indexes have not been rebuilt/reorganized. I have worked primarily on SQL 2005 but with 2000 I am not familiar with Logical vs Extent fragmentation. And on the 2000 server there is high Logical Fragmentation (1000+%). With me rebuilding the indexes on the 2000 server databases, will this reduce performance or halt functionality of the servers while this process is running???
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Jun 2, 2014
We have few tables where we do truncate load or only do insert activities , why do the cluster index get fragmented very often to > 80%?
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Nov 20, 2007
I need to manage the problem of negative performance implications when I fragment a 1TB+ DB. I want to perform Index Reorganization if fragmentation is no higher than 30%, and Index Rebuild if the fragmentation exceeds 30%.
Firstly can anyone recommend a script which uses sys.dm_db_index_physical_stats system to ascertain the
fragmentation level. Secondly, is there a technique I can employ to prevent the ONLINE operation completely killing performance on 27/4 production system?
ALTER INDEX REORGANIZE/REBUILD WITH (ONLINE=ON)
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Mar 18, 2008
Hi,
I just want to know whether any advantage or disadvantage
in doing Reorganize Index And Rebuild Index ....
Plz do comment on this ASAP !!!!
Thanks in advance
Regards
Arv
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Mar 18, 2008
Hi,
I just want to know whether any advantage or disadvantage
in doing Reorganize Index And Rebuild Index ....
Plz do comment on this ASAP !!!!
Thanks in advance
Regards
Arv
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Jan 23, 2015
I have a table that has a clustered index that is only the identity column on the table. The table is somewhere around 200K rows and has 3800 pages in the index. We run our index maintenance every other day on this database using Ola's scripts and this index is rebuilt because it is 40-60% fragmented after 2 days. Overall, this isn't really too much of a problem since the index rebuild doesn't take too long, but I am puzzled as to how this index is getting fragmented since the only column in it is the identity.
CREATE TABLE [dbo].[Example](
[ExampleID] [int] IDENTITY(1,1) NOT NULL,
[ExampleCode] [varchar](10) NOT NULL,
[ForeignID] [int] NOT NULL,
[AnotherID] [int] NOT NULL,
[code]...
) ON [PRIMARY]There is nothing strange like updates to the identity happening and while some records are deleted, there has only been about 20,000 in the life of the table (months). Not enough to account for the level of fragmentation that we're seeing on the index.About the only thing I can think of that would cause fragmentation on this index in this scenario are:
1. Page splits caused by starting with a small value in one of the VARCHARs and later inserting a larger value
2. Page splits caused by the NULLABLE column, ExampleDate, starting with NULLs and later updating them to a date.
For #1, I had development check the update scenarios for the varchar columns, especially the varchar(1000) one, and they didn't see it as a common thing where the values would go from small (or empty) to large.
For #2, I checked and found that the only value for that column in the table is NULL so while it always starts as NULL, it never gets updated to anything else.
I've tried looking at sys.dm_db_index_operational_stats and the leaf_update_count is around 300,000, but unless those updates are causing page splits, I don't see how they would contribute to fragmentation.
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Sep 17, 2007
I have a non-clustered index on a table. If I rebuild or reorganize it in SQL 2005, the total fragmentation percent reported by properties/fragmentation on the index stays at 33%.
Why doesn't the fragmentation go to 0% ?
If I totally drop/create the index, starts even higher, but beorg or rebuild simply goes to 33%. This even if using with use temp db for sort option.
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Dec 11, 2007
I have been reworking my index maintenance jobs from my old SQL 2000 table and view references to the DMV's and System Tables in SQL 2005, and I noted that some of my indexes end up being more fragmented after a reorganization and or rebuild. That doesn't make much sense to me at all. The code I am executing is:
Code Block
print ' '
print '************* Beginning Index Updates for '+db_name()+' *************'
print ' '
DECLARE @tablename varchar(250),
@indexname varchar(250),
@fragpcnt decimal(18,1),
@indexid int,
@dbID int
-- Determine DB ID
SELECT @dbID = DB_ID()
DECLARE tnames_cursor CURSOR FOR
SELECT b.name, c.name, a.avg_fragmentation_in_percent, a.index_id
FROM sys.dm_db_index_physical_stats (@dbID, NULL, NULL, NULL, NULL) a
JOIN sys.indexes b ON a.object_id = b.object_id
AND a.index_id = b.index_id
JOIN Sys.objects c ON b.object_id = c.object_id
WHERE a.index_id > 0
ORDER by a.page_count DESC
OPEN tnames_cursor
FETCH NEXT FROM tnames_cursor INTO @indexname, @tablename, @fragpcnt, @indexid
WHILE (@@fetch_status = 0)
BEGIN
-- Declare and determine the tablename ID
declare @tablenameID int
select @tablenameID = object_id(@tablename)
IF @fragpcnt > 30
BEGIN
EXEC('ALTER INDEX ['+@indexname+'] ON ['+@tablename+'] REBUILD')
PRINT '***************************************************'
PRINT 'Index '+@indexname+' was rebuilt.'
PRINT 'Original framentation Percent: ' + convert(varchar, @fragpcnt) + '%'
SELECT @fragpcnt = avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (@dbID, @tablenameID, @indexid, NULL, NULL) a
JOIN sys.indexes b ON a.object_id = b.object_id
AND a.index_id = b.index_id
JOIN Sys.objects c ON b.object_id = c.object_id
PRINT 'Post Rebuild fragmentation Percent: ' + convert(varchar, @fragpcnt) + '%'
PRINT ''
END
ELSE IF @fragpcnt BETWEEN 5 AND 30
BEGIN
EXEC('ALTER INDEX ['+@indexname+'] ON ['+@tablename+'] REORGANIZE')
PRINT '***************************************************'
PRINT 'Index '+@indexname+' was Reorganized.'
PRINT 'Original framentation Percent: ' + convert(varchar, @fragpcnt) + '%'
SELECT @fragpcnt = avg_fragmentation_in_percent
FROM sys.dm_db_index_physical_stats (@dbID, @tablenameID, @indexid, NULL, NULL) a
JOIN sys.indexes b ON a.object_id = b.object_id
AND a.index_id = b.index_id
JOIN Sys.objects c ON b.object_id = c.object_id
PRINT 'Post Reorganization fragmentation Percent: ' + convert(varchar, @fragpcnt) + '%'
PRINT ''
END
ELSE
BEGIN
PRINT '***************************************************'
PRINT 'Index '+@indexname+' was left alone.'
PRINT 'Original framentation Percent: ' + convert(varchar, @fragpcnt) + '%'
PRINT ''
END
FETCH NEXT FROM tnames_cursor INTO @indexname, @tablename, @fragpcnt, @indexid
END
print ' '
print '************* NO MORE TABLES TO INDEX *************'
PRINT 'All indexes for the '+db_name()+' database have been updated.'
print ' '
DEALLOCATE tnames_cursor
Below are some snipits of the output:
***************************************************
Index _dta_index_wuci_history_8_1123587141__K2_K5 was rebuilt.
Original framentation Percent: 58.3%
Post Rebuild fragmentation Percent: 58.3%
***************************************************
Index PK__batchjob__776C5C84 was left alone.
Original framentation Percent: 0.0%
***************************************************
Index PK__ContactWebDetail__116A8EFB was rebuilt.
Original framentation Percent: 44.4%
Post Rebuild fragmentation Percent: 77.8%
***************************************************
Index PK__managed_object_s__5DCAEF64 was left alone.
Original framentation Percent: 0.0%
***************************************************
Index kb_IX_kb_scope_scope_role was rebuilt.
Original framentation Percent: 75.0%
Post Rebuild fragmentation Percent: 87.5%
***************************************************
Index PK__query__09A971A2 was left alone.
Original framentation Percent: 0.0%
***************************************************
Index PK__email_message__38996AB5 was rebuilt.
Original framentation Percent: 85.7%
Post Rebuild fragmentation Percent: 0.0%
***************************************************
If the index begins with PK, then it is the primary key index which is generally the clustered index on the table, but not always. If it has an IX on it, it is generally a non-clustered index on the table, but again not always. In the case of the above, the PK is a clustered index, and the IX is a non-clustered index.
Anyone have any ideas why this is functioning in this manner?
Thanks,
Jon
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Jun 26, 2015
In my database all columns have Identity Value as a PK.
Now today I check Index Fragmentation I saw that many cluster and Non cluster Index are avg.Fragmentation is around 99 % I thought that in Identity column record is always inserted at bottom so there is no fill factor assigned to it.
So in this case Do I need to set Fill factor for Cluster and Non Cluster Index?
If Yes Then For PK How much - 95 % or what? and same for Non cluster or It should around 85 to 90
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Dec 17, 2014
I've noticed that indexes in my AX 2012 database get very fragmented very quickly. Is this normal and that I should just defragment them regularly or is there a possible issue here that needs investigated?
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Jul 20, 2005
hello everyone,we dropped the clustered & nonclustered indeces on a table, thenrebuilt them. logical fragmentation is near zero, but extentfragmentation is about 40%. how can this be if the indeces are brandnew?
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Jun 29, 2001
Running SQL 7.0 SP3 on P3 dual 800.
I rebuild indexes every night as part of the maintenance plan. Usually it takes about 1 hr 10 minutes on a 15 G db, last night it took 9 hrs.
I have no idea why it would take so long. Nothing changed, there were no new indexes created and none deleted.
Any ideas? I have to find out why. My boss wants an answer.
Thanks in advance.
Kelsey
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Nov 1, 2006
Hi All,
Is there any way to calculate how big the transaction log will grow during the rebuilding of the indexes?
Thanks.
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Jan 11, 2006
I run dbcc dbreindex command and send the output to the text file. Is there any other way to check that indexes were in fact rebuild?
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Jan 15, 2008
Rebuild Index job for user db's is failing, one user db is a huge size 120 GB. The job scheduled to run every sunday 1 AM
I found the below error in log report
Rebuild Index Task (server name)
Rebuild index on Local server connection
Databases: All user databases
Object: Tables and views
Original amount of free space
Task start: 01/13/2008 1:26 AM.
Task end: 01/13/2008 2:38 AM.
Failed-1073548784) Executing the query "ALTER INDEX [Idx_CISCO_WLC_EVENTID] ON [dbo].[CISCO_WLC_200711262137] REBUILD WITH ( PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, SORT_IN_TEMPDB = OFF, ONLINE = OFF )
" failed with the following error: "Cannot find the object "dbo.CISCO_WLC_200711262137" because it does not exist or you do not have permissions.". Possible failure reasons: Problems with the query, "ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.
Please let me know the solution?
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Apr 26, 2015
We have a database with a table that contains around 180m records. Each day a further 70k are inserted. No records are ever deleted as this table is used for archiving only.Users are required to perform SELECTs on this table constantly but due to the high number of INSERTs the indexes become very fragmented very quickly. My aim is to avoid daily rebuilds of the indexes which is what our software house is telling us we have to do.
This is the DDL for the table:
CREATE TABLE [dbo].[Inventory](
[EAN] [bigint] NOT NULL,
[Day] [smalldatetime] NOT NULL,
[State] [int] NOT NULL,
[Quantity] [int] NULL,
[StockValue] [float] NULL,
CONSTRAINT [PK_Inventory] PRIMARY KEY CLUSTERED
[code]...
There are also three clustered Indexes on this table each referencing a single column. The problem from my side is that I cannot understand why the three columns in a primary key would also be configured as non-clustered indexes.My solution would be one of the following:
1. Accept the tables are going to be fragmented and require a daily rebuild (don't like this one!)
2. Partition the table
3. Remove the non-clustered Indexes and let the clustered index for the primary key do the work.
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Dec 19, 2000
Hi all...
I have a table with over 60 million rows (approx 20GB) which has an indexed column. I have tried using DBC DBReindex to rebuild the index, but after kicking it off on a friday, it is still running the following wednesday. Since managers and other finicky types access this database, that's not acceptable (it slows down their reporting).
Is there a way to speed up the reindexing process? Perhaps by adding space to the tempdb (it's 500MB) or putting it in RAM temporarily? I haven't seen any articles that specifically state that TEMPDB is used during an index rebuild, but it seems logical that it would be.
Any suggestions to speed up the process would be most appreciated!
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Oct 3, 2007
Hi,
After issuing an index rebuild on a primary key index (and updating statistics), the index still shows a scan density of 12.5%!
Any ideas on why the rebuild doesn't seem to do anything on the fragmentation levels?
I'm using sql 2005
Thanx
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