High Extent Scan Fragmentation
Oct 25, 2002
Can anyone let me now why the extent scan fragmentation is very high.
I do have a clustered index on this table .
The fill factor is 0 and this table has high inserts as it is used to maintain history.
Rebuilding the Indexes did not help.
DBCC SHOWCONTIG scanning 'ACCOUNTS' table...
Table: 'ACCOUNTS'(1061578820); index ID: 1, database ID: 5
TABLE level scan performed.
- Pages Scanned................................: 728157
- Extents Scanned..............................: 91759
- Extent Switches..............................: 93305
- Avg. Pages per Extent........................: 7.9
- Scan Density .......: 97.55% [91020:93306]
- Logical Scan Fragmentation ..................: 0.33%
- Extent Scan Fragmentation ...................: 99.99%
- Avg. Bytes Free per Page.....................: 76.6
- Avg. Page Density (full).....................: 99.05%
DBCC execution completed. If DBCC printed error messages, contact your system administrator
Thanks in advance,
Shades[B]Extent Scan Fragmentation
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Dec 28, 2007
On some tables when I run DBCC ShowContig followed by DBReindex followed by ShowContig I notice Extent Scan Fragmentation actually increases. Why does this happen? Below are the SHOWCONTIG results after running DBReindex three times.
After First DBReindex
- Pages Scanned................................: 986
- Extents Scanned..............................: 124
- Extent Switches..............................: 123
- Avg. Pages per Extent........................: 8.0
- Scan Density [Best Count:Actual Count].......: 100.00% [124:124]
- Logical Scan Fragmentation ..................: 0.00%
- Extent Scan Fragmentation ...................: 47.58%
- Avg. Bytes Free per Page.....................: 91.0
- Avg. Page Density (full).....................: 98.88%
After Second DBReindex
- Pages Scanned................................: 986
- Extents Scanned..............................: 124
- Extent Switches..............................: 123
- Avg. Pages per Extent........................: 8.0
- Scan Density [Best Count:Actual Count].......: 100.00% [124:124]
- Logical Scan Fragmentation ..................: 0.00%
- Extent Scan Fragmentation ...................: 20.16%
- Avg. Bytes Free per Page.....................: 91.0
- Avg. Page Density (full).....................: 98.88%
After Third DBReindex
- Pages Scanned................................: 986
- Extents Scanned..............................: 124
- Extent Switches..............................: 123
- Avg. Pages per Extent........................: 8.0
- Scan Density [Best Count:Actual Count].......: 100.00% [124:124]
- Logical Scan Fragmentation ..................: 0.00%
- Extent Scan Fragmentation ...................: 67.74%
- Avg. Bytes Free per Page.....................: 91.0
- Avg. Page Density (full).....................: 98.88%
Thanks, Dave
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Jul 18, 2007
Hello. When reviewing the DBCC SHOWCONTIG immediately after reindexing all indexes on a database, I see the ExtentFragmentation has values like 50 to 70%... These are SQL 2005 tables with clustered PK's, no large varchars/blobs, and at least 100 pages in the index... The numbers related to PAGE fragmentation are ok after reindexing, but not the EXTENT fragmentation numbers.
I noticed the drive is in need of being defragged at the disk level. Is that a reason why reindexing doesn't fix the Extent frag numbers?? ANy other ideas on this? I can try defragging the DISK over the weekend, bringing the database offline then, but any other thougths on why the Extents show these high %'s? Is there any command to reset them and maybe that isn't happening? Like must I do update usage to get valid Extent frag #'s??
If there were MANY autogrows on the files, is that a different level of fragmentation? and how could all those small pieces of files be pulled back together? Thanks, Bruce
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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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Aug 16, 2007
I have a table with 50% Logical Scan Fragmentation. [ according to Dbcc Showcontig (myTable) ]
Why after running DBCC INDEXDEFRAG (myDB,myTable) does it still sit at 50%.
Why isn't it lower?
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Jan 29, 2006
How can I improve performance of my search if I am looking in a table with more than ten million rows with a "like query"?
Does putting an index mean only telling the computer to start in a particular order?
if I index all the coloums does my search get faster ?
how can I decide on an indexing strategy?
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Apr 23, 2007
Hi,
Is there a way to configure mirroring to go from High Availability to High Protection without having to reconfigure Database Mirroring? Using the interface in Management Studio, I can change the configuration option to High Performance, but not High Protection despite both of them being Synchronous.
If not, what are the recommended steps to configure the mirror once it already has been configured? Is just like initially setting up the mirror or would there be any shortcuts I could take? If I stop the mirroring and remove the witness, will the High Protection option be available?
Thanks,
J.
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Mar 6, 2008
Hi There
I realise this is a stupid quesiton but i cannot really find any confirmation of this in BOL.
If you are running High Safety with automatic failover, when failover occurs does this automatically change to High Performance mode. SInce for failover to occur something has happen with the primary , it will be impossible to commit transactions on the new primary and mirror asyncronously since 1 of them is no longer available.
So am i correct in assuming that automatic failover also automatically changes the mode to High Performacne for that session?
Thanx
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May 6, 2004
I've faced with this problem in my DB:
There are some tables that suffer inserts and deletes daily. These tables have 3 nonclustered indexes including the pk.
I perceived that the space used for these tables are growing day after day even ocurring daily deletes.
These inserts and deletes follow the keys of the pk in ascent order.
I ran DBCC SHOWCONTIG on the tables and got results like this:
- Avg. Bytes Free per Page.....................: 7996.3
When I transform the pk to clustered this problem doesn't happen.
You realized the consequence of this: the users complains because the DB is without space, but it's not true!
Anybody could help me to understand why the extents are not being deallocated?
Thank's for help!
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Jul 16, 2007
Hi, all,
Again I am confused about the extent of being convinced by the mining models. We can validate the models with accuracy chart, but then to what extent can we trust that? (you never get 100% correct miming models) If we dont trust the results of the models, then the patterns the models discover are meaningless.
Just need some advices from you experts here to help me convince people on what I got from my mining models.
I am looking forward to hearing from you shortly and thank you very much.
With best regards,
Yours sincerely,
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Oct 4, 2007
Hey,
what is the difference between Table Scan und Index Scan?
I find no difitions in the internet
Finchen
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Sep 21, 2007
Hi,
I want to know wht is a
TABLE SCAN
INDEX SCAN
INDEX SEEKand When they are used, Wht is the difference between all these.????
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Sep 20, 2006
Hi,
This is on Sybase but I'm guessing that the same situation would happen on SQL Server. (Please confirm if you know).
I'm looking at these new databases and I'm seeing code similar to this all over the place:
if not exists (select 1 from dbo.t1 where f1 = @p1)
begin
select @errno = @errno | 1
end
There's a unique clustered in dex on t1.f1.
The execution plan shows this for this statement:
FROM TABLE
dbo.t1
EXISTS TABLE : nested iteration.
Table Scan.
Forward scan.
Positioning at start of table.
It's not using my index!!!!!
It seems to be the case with EXISTS statements. Can anybody confirm?
I also hinted to use the index but it still didn't use it.
If the existence check really doesn't use the index, what's a good code alternative to this check?
I did this and it's working great but I wonder if there's a better alternative. I don't really like doing the SET ROWCOUNT 1 and then SET ROWCOUNT 0 thing. SELECT TOP 1 won't work on Sybase, :-(.
SET ROWCOUNT 1
SELECT @cnt = (SELECT 1 FROM dbo.t1 (index ix01)
WHERE f1 = @p1
)
SET ROWCOUNT 0
Appreciate your help.
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Oct 8, 2007
I write a work about database, and I want to write the diffrence between Table scan and Index scan. When is the index scan effectient? Use the database a Table scan when there is an index on the table or always a index scan when the index is nonselective? Can be a Table Scan effecient than a index scan?
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May 13, 2008
i want to do fragmentation using SQL 2005 Express. Can their be any helping material for making fragmentation. Any Example
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Mar 29, 2001
What DBCC or otherwise one would be able to find table fragmentation in SQL 7 and how to take some proactive actions ?
Thanks very much for your time.
-Tim
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Jun 1, 2004
Would someone please let me know which is the better way to reduce fragmentation on Windows:NT drive?
dbcc indexdefrag
or
dbcc reindex
or
dropping and recreating indexes through SQL?
Thanks
Vinnie
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Jul 27, 2007
Sql Server 2000.
For simplicity, I am avoiding minor details.
Here is a scenario.
Create Table T (T_ID int PK, €¦..) and this table is referenced by 20 other places on T_ID.
And these 20 tables have T_ID as PK or part of PK.
We have large volume of deletes in T and in the other 20 tables based on T_ID.
Once the deletes are done, will dropping and re-creating the FK€™s that reference the T_ID
help reduce the fragmentation caused by the deletes?
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Aug 14, 2001
I am having problems w/ the indexes on a particular table. Currently the scan density if 25%. I have ran the dbcc dbreindex and the scan density does not improve. I have manually dropped and recreated all of the indexes on the table (there are only two) and still no help.
I have a clustered Primary Key index on my part_number and project_number fields and another index on the project_number field. If I drop the second index and only have my primary key index, it still doesn't help. The fill factor was originally set to 90% and I changed this to 30%, 20%, 10%, 0% and the best scan density I could acheive was 50%.
The data in this table is not updated that often, on average about 15 records a day are updated, and there are only 107 records. This is a small table, but there is a possibility for it to grow rapidly and I want to be prepared now.
Does anyone have any ideas or suggestions? I've tried everything I can think of with no luck.
TIA,
Chris
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May 26, 2000
Can anyone tell me how to get rid of the Table Scan(1 million rows)being performed on the
The last line, option (loop loin) stopped table scanning the B.ss_manifest and started using the index, I'd like both tables to use the index.
This is the argument I get from execution plan under the table scan.
Object ((D4000).(dbo).(shipstop)as (A))
update drivers set dr_miles_run = case when D1.miles > 0 then d1.miles else 0 end
from (select mf_dr_nbr, sum( case when A.ss_end_dt < '05/17/00' then
( cast((datediff(day, '05/17/00' , B.ss_end_dt ) + 1) as float) /
cast( (datediff(day, A.ss_end_dt , B.ss_end_dt ) + 1) as float) * mf_ld_miles)
else mf_ld_miles end) as miles
from manifest, shipstop A, shipstop B
where mf_manifest_nbr = A.ss_manifest_nbr
and mf_manifest_nbr = B.ss_manifest_nbr
and A.ss_stop_type in ('OR','SA')
and B.ss_stop_type in ('DT','RD')
and ((A.ss_end_dt >= '05/17/00 00:00' and A.ss_end_dt < '05/24/00 00:00')
OR ((B.ss_end_dt >= '05/17/00 00:00' and B.ss_end_dt < '05/24/00 00:00'))) and mf_status > 3 group by mf_dr_nbr ) as D1
where Drivers.dr_driver_nbr = D1.mf_dr_nbr
option (loop join)
Thanks for any ideas!
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Aug 21, 2006
Hi,
I have a simple temp table which looks like this:
CREATE TABLE #t7e07c01fa80143ff84cb14a2307809f7
(
[AUTOID_TEMP] [int] IDENTITY (1, 1) NOT NULL,
...
)
ON [PRIMARY]
ALTER TABLE #t7e07c01fa80143ff84cb14a2307809f7 ADD
CONSTRAINT [PK_t7e07c01fa80143ff84cb14a2307809f7] PRIMARY KEY NONCLUSTERED
(
[AUTOID_TEMP]
)
ON [PRIMARY]
Insert Into #t7e07c01fa80143ff84cb14a2307809f7
Selet columns... from t....
-- get total records
Declare @TotalCount as int
select @TotalCount = count(AUTOID_TEMP) from #t7e07c01fa80143ff84cb14a2307809f7
Now the above last statement does a index scan. I am new to indexing/tuning and was wondering if its normal - if so why and can I somehow enhance this?
Thanks
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Nov 1, 2007
Hey guys,
I have a procedure that runs everyday which takes the IIS log file from the previous day and imports it and calcs values. I would like to change this from taking the previous day to scanning all the file names in the folder and comparing them to a database to see if they have already been scanned before. I already have a table called DatesScanned which lists the filename and scandate.
IE:
D:Logsfile1.log
D:Logsfile2.log
D:Logsfile3.log
D:Logsfile4.log
The 4 file names will be scanned and compared to DatesScanned to see which has been imported already.
Can anyone point me to a resource or information on how I would get the directory listing of a folder so I could compare it to the DatesScanned table.
Thanks a bunch!
Jeff
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Jul 23, 2005
Hi,Can someone please explain the following1. Meaning of scan count as reported when "statistics io" is turned onprior to running a query.2. In which situations could you have an identical database runningon two diferent servers , with identical database serverconfigurations, running identical queries, with identical query plan,report large discrepency in the scan count . This is one of thepossibilities we are looking at in terms of the reason why one serverruns the job in 12 hours and the other in 24 hours.Server 1--------Table 'TRANS_HISTORY'. Scan count 216, logical reads 897093, physicalreads 44, read-ahead reads 900599.SQL Server Execution Times:CPU time = 27766 ms, elapsed time = 46850 ms.UNIT_NUMBERACCOUNT_TYPETRANSACTION_TYPEServer 2--------Table 'TRANS_HISTORY'. Scan count 491, logical reads 952759, physicalreads 51, read-ahead reads 954414.SQL Server Execution Times:CPU time = 31563 ms, elapsed time = 145595 ms.UNIT_NUMBERACCOUNT_TYPETRANSACTION_TYPEI thank you in advance for your assistance.Puvendran
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Jul 9, 2007
Does SQL Server allow a table scan to be used when querying a table that has a clustered-index? If yes, could someone please show me the syntax? I have tried with (index(0)) but this appararently means a clustered index scan when there is a clustered index on the table to be queried.
Or does clustered index scan mean the same thing as a table scan when the table has a clustered index? Confused.
Thanks
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Nov 28, 2007
Friends,
I am using this query in a table with 29,000 records having non-clustered index on emp_id
select * from employee
where emp_id between 100 and 1000
and gender = 'M'
order by emp_id
execution plan shows a table scan in table employee. Any reason?
select * from employee with (index = emp_id)
where emp_id between 100 and 1000
order by emp_id
ofcourse this uses index seek
regards,
Priw
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May 21, 2007
I do not understand it but by connection to my database seems to keep crapping out. I get the below error and my app appears to be unable to access the connection. Then a couple restarts later it tells me that my login under my Windows User failed . The database is there and besides maybe a couple records longer there isnt anything corrupt about the data, and in fact, if I restart the entire PC most times it will allow me to connect again. I can even still access the data tables through the C# editor. Any idea why this error is being thrown?
Thx
Code SnippetSystem.Data.SqlClient.SqlException was unhandled
Message="A system assertion check has failed. Check the SQL Server error log for details
The log scan number (35:460:2) passed to log scan in database 'F:\PDLOGSHEET\PDLOGSHEET\BIN\DEBUG\DATABASE1.MDF' is not valid. This error may indicate data corruption or that the log file (.ldf) does not match the data file (.mdf). If this error occurred during replication, re-create the publication. Otherwise, restore from backup if the problem results in a failure during startup.
An error occurred during recovery, preventing the database 'F:\PDLOGSHEET\PDLOGSHEET\BIN\DEBUG\DATABASE1.MDF' (database ID 26) from restarting. Diagnose the recovery errors and fix them, or restore from a known good backup. If errors are not corrected or expected, contact Technical Support.
Cannot open user default database. Login failed.
Login failed for user 'GC\cbcottier'.
Location: logscan.cpp:1925Expression: UtilDbccIsInsideDbcc ()SPID: 51Process ID: 3640
Location: logscan.cpp:1925Expression: UtilDbccIsInsideDbcc ()SPID: 51Process ID: 3640"
Source=".Net SqlClient Data Provider"
ErrorCode=-2146232060
Class=20
LineNumber=65536
Number=3624
Procedure=""
Server="\\.\pipe\E74940B1-0BD7-42\tsql\query"
State=1
StackTrace:
at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
at System.Data.SqlClient.SqlConnection.Open()
at System.Data.Common.DbDataAdapter.FillInternal(DataSet dataset, DataTable[] datatables, Int32 startRecord, Int32 maxRecords, String srcTable, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataTable[] dataTables, Int32 startRecord, Int32 maxRecords, IDbCommand command, CommandBehavior behavior)
at System.Data.Common.DbDataAdapter.Fill(DataTable dataTable)
at PDLogSheet.Database1DataSetTableAdapters.ReportTitlesTableAdapter.Fill(ReportTitlesDataTable dataTable) in F:PDLogSheetPDLogSheetDatabase1DataSet.Designer.cs:line 4362
at PDLogSheet.frmLogSheet.frmLogSheet_Load(Object sender, EventArgs e) in F:PDLogSheetPDLogSheetfrmLogSheet.cs:line 42
at System.Windows.Forms.Form.OnLoad(EventArgs e)
at System.Windows.Forms.Form.OnCreateControl()
at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
at System.Windows.Forms.Control.CreateControl()
at System.Windows.Forms.Control.WmShowWindow(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ContainerControl.WndProc(Message& m)
at System.Windows.Forms.Form.WmShowWindow(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.SafeNativeMethods.ShowWindow(HandleRef hWnd, Int32 nCmdShow)
at System.Windows.Forms.Control.SetVisibleCore(Boolean value)
at System.Windows.Forms.Form.SetVisibleCore(Boolean value)
at System.Windows.Forms.Control.set_Visible(Boolean value)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at PDLogSheet.Program.Main() in F:PDLogSheetPDLogSheetProgram.cs:line 17
at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
at System.Runtime.Hosting.ManifestRunner.Run(Boolean checkAptModel)
at System.Runtime.Hosting.ManifestRunner.ExecuteAsAssembly()
at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext, String[] activationCustomData)
at System.Runtime.Hosting.ApplicationActivator.CreateInstance(ActivationContext activationContext)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
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Oct 29, 2007
Hi All,
When an end user view a report using report manager or a custom build web site, would query of the report scan the tables in original data base? In this case it is a OLTP data base.
Thanks
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May 8, 2001
hi all,
i have inherited a database running on sql7 sp2. a lot of the tables do not have a clustered index. some of these tables are highly fragmented. below is a sample of the dbcc showcontig output
TABLE level scan performed.
- Pages Scanned................................: 104934
- Extents Scanned..............................: 13124
- Extent Switches..............................: 13123
- Avg. Pages per Extent........................: 8.0
- Scan Density [Best Count:Actual Count].......: 99.95% [13117:13124]
- Extent Scan Fragmentation ...................: 5.84%
- Avg. Bytes Free per Page.....................: 7757.4
- Avg. Page Density (full).....................: 4.16%
this table has 5 non-null char columns whose total length is 43 chars and the table occupies about 900 mb for only about 670,000 rows!
select on the table sucks!
since there is no clustered index i have to rebuild the table to remove the fragmentation. is there a way to reorganize the table without recreating it?
thanx
:-)
hemant
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Oct 13, 2000
Hi!
I have a problem with defragmenting the tables. When i ran dbcc showcontig for the tables, it shows 94%, 50%, 33% fragmentations . I have rebuild indexes on all those tables and ran dbcc showcontig again but still it shows the same % of fragmentations. Is there any way to remove fragmentation on all the tables completely. Any help would be appreciated.
Thanks,
Saran
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Apr 14, 2004
One of my production servers has been determined to be 92% fragmented.
What's the proper procedure for defraging a database server?
I couldn't find anything very helpful in BOL, nor Knowledge Base.
Sidney Ives
Database Administrator
Sentara Healthcare
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Aug 9, 2004
What's the best way to find out if disk fragmentation on Windows 2000 Server is affecting SQL Server performance?
If disk fragmentation is shown to be a cause of performance problems, what are the recommendations for a disk fragmentation strategy? eg. use the win 2000 built in disk defrag utility or buy a 3rd party product like DiskKeeper? How much of an overhead is a product like DiskKeeper that defrags in the background?
Clive
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Oct 1, 2004
Hello,
How can I mesure the database fragmentation ? Cause DBCC SHOWCONTIG shows obects fragmentation only. I would like to see the whole database fragmentation.
Thanks for help
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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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