<a href="http://g.adspeed.net/ad.php?do=clk&zid=15220&wd=468&ht=60&pair=as" target="_blank"><img style="border:0px;" src="http://g.adspeed.net/ad.php?do=img&zid=15220&wd=468&ht=60&pair=as" alt="i" width="468" height="60"/></a>
Log in
::
Register
::
Not logged in
Home
Tags
Articles
Editorials
Stairways
Forums
Scripts
Videos
Blogs
QotD
Books
Ask SSC
SQL Jobs
Training
Authors
About us
Contact us
Newsletters
Write for us
<a href="http://g.adspeed.net/ad.php?do=clk&zid=15491&wd=120&ht=300&pair=as" target="_top"><img style="border:0px;" src="http://g.adspeed.net/ad.php?do=img&zid=15491&wd=120&ht=300&pair=as" alt="i" width="120" height="300"/></a>
Recent Posts
Recent Posts
Popular Topics
Popular Topics
Home
Search
Members
Calendar
Who's On
Home
»
SQL Server 2008
»
SQL Server 2008 - General
»
slow dm_db_index_physical_stats query
slow dm_db_index_physical_stats query
Rate Topic
Display Mode
Topic Options
Author
Message
Steve Malley
Steve Malley
Posted Tuesday, October 16, 2012 11:34 AM
SSC Rookie
Group: General Forum Members
Last Login: Friday, March 08, 2013 8:10 AM
Points: 30,
Visits: 135
I have a query I use to report on index fragmentation.
SELECT TOP 25
db.name AS 'DatabaseName'
, SCHEMA_NAME(obj.schema_id) AS 'SchemaName'
, OBJECT_NAME(ps.OBJECT_ID) AS 'TableName'
, db_id() AS 'DatabaseID'
, ps.OBJECT_ID AS 'ObjectID'
, ps.index_id AS 'IndexID'
, ps.partition_number AS 'PartitionNum'
, cast(ps.avg_fragmentation_in_percent as [dec](16,2)) AS 'FragPercent'
, cast(ps.page_count*8192.0/1048576 as dec(16,2)) AS 'PagesMB'
FROM sys.databases db
INNER JOIN sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL , NULL, N'Limited') ps
ON db.database_id = ps.database_id
INNER JOIN sys.objects obj ON ps.object_id = obj.object_id
WHERE ps.avg_fragmentation_in_percent >= 10
ORDER BY
cast(ps.page_count*8192.0/1048576 as dec(16,2)) DESC
,cast(ps.avg_fragmentation_in_percent as [dec](16,2)) DESC
In some environments this runs quickly. In others it is *slow*. Does anyone know why this would be the case? Had similar experience
Post #1373432
GilaMonster
GilaMonster
Posted Tuesday, October 16, 2012 12:40 PM
SSC-Dedicated
Group: General Forum Members
Last Login: Today @ 11:58 AM
Points: 37,665,
Visits: 29,918
Size of tables, throughput of IO subsystem.
Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass
Post #1373468
Perry Whittle
Perry Whittle
Posted Tuesday, October 16, 2012 12:56 PM
SSCertifiable
Group: General Forum Members
Last Login: Today @ 9:47 AM
Points: 5,201,
Visits: 11,151
Number of indexes?
-----------------------------------------------------------------------------------------------------------
"Ya can't make an omelette without breaking just a few eggs"
Post #1373478
Steve Malley
Steve Malley
Posted Wednesday, October 17, 2012 7:20 AM
SSC Rookie
Group: General Forum Members
Last Login: Friday, March 08, 2013 8:10 AM
Points: 30,
Visits: 135
Since I am only accessing the system catalog and a DMV, I would expect that performance should be consistent and fast. I find that it is not. It may just be the volume of records, but it is a bit weird that these objects are responsive in some environments, but not responsive in others.
Post #1373778
Sean Pearce
Sean Pearce
Posted Wednesday, October 17, 2012 7:36 AM
Old Hand
Group: General Forum Members
Last Login: Today @ 9:49 AM
Points: 341,
Visits: 1,308
Steve Malley (10/17/2012)
Since I am only accessing the system catalog and a DMV, I would expect that performance should be consistent and fast. I find that it is not. It may just be the volume of records, but it is a bit weird that these objects are responsive in some environments, but not responsive in others.
http://www.sqlskills.com/blogs/paul/post/Inside-sysdm_db_index_physical_stats.aspx
The idea of the DMV is to display physical attributes of indexes (and the special case of a heap) - to do this it has to scan the pages comprising the index, calculating statistics as it goes. Many DMVs support what's called predicate pushdown, which means if you specify a WHERE clause, the DMV takes that into account as it prepares the information. This DMV doesn't. If you ask it for only the indexes in the database that have logical fragmentation > 30%, it will scan all the indexes, and then just tell you about those meeting your criteria. It has to do this because it has no way of knowing which ones meet your criteria until it analyzes them - so can't support predicate pushdown.
http://thesqlguy.blogspot.com/
Post #1373786
GilaMonster
GilaMonster
Posted Wednesday, October 17, 2012 7:57 AM
SSC-Dedicated
Group: General Forum Members
Last Login: Today @ 11:58 AM
Points: 37,665,
Visits: 29,918
Steve Malley (10/17/2012)
Since I am only accessing the system catalog and a DMV, I would expect that performance should be consistent and fast.
Except that DMV is not a view into memory (as most of them are), but a way to go and read the non-leaf levels of every table in the DB and calculate results based off that. Hence, the larger the DB and the slower the IO subsystem, the slower that query will run
Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass
Post #1373801
Steve Malley
Steve Malley
Posted Thursday, October 18, 2012 7:08 AM
SSC Rookie
Group: General Forum Members
Last Login: Friday, March 08, 2013 8:10 AM
Points: 30,
Visits: 135
Thanks. That makes sense now. I appreciate your replies.
Post #1374324
« Prev Topic
|
Next Topic »
Permissions
You
cannot
post new topics.
You
cannot
post topic replies.
You
cannot
post new polls.
You
cannot
post replies to polls.
You
cannot
edit your own topics.
You
cannot
delete your own topics.
You
cannot
edit other topics.
You
cannot
delete other topics.
You
cannot
edit your own posts.
You
cannot
edit other posts.
You
cannot
delete your own posts.
You
cannot
delete other posts.
You
cannot
post events.
You
cannot
edit your own events.
You
cannot
edit other events.
You
cannot
delete your own events.
You
cannot
delete other events.
You
cannot
send private messages.
You
cannot
send emails.
You
may
read topics.
You
cannot
rate topics.
You
cannot
vote within polls.
You
cannot
upload attachments.
You
may
download attachments.
You
cannot
post HTML code.
You
cannot
edit HTML code.
You
cannot
post IFCode.
You
cannot
post JavaScript.
You
cannot
post EmotIcons.
You
cannot
post or upload images.
Copyright © 2002-2013 Simple Talk Publishing. All Rights Reserved.
Privacy Policy.
Terms of Use.
Report Abuse.
