Missing Indexes in SQL Server 2005

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Missing Indexes in SQL Server 2005

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Ranga N

Posted Monday, September 15, 2008 9:48 PM

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Comments posted to this topic are about the item Missing Indexes in SQL Server 2005

Post #569915

Jeff Moden

Posted Monday, September 15, 2008 11:28 PM

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Great info! I gotta try it. Thanks.

--Jeff Moden

"RBAR is pronounced "ree-bar" and is a "Modenism" for "Row-By-Agonizing-Row".

First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column."

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Post #569936

marshall.jones

Posted Tuesday, September 16, 2008 12:42 AM

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this is super handy.

does anyone know if i can truncate these tables at any time safely (for example before running a test load for example).

Post #569961

GilaMonster

Posted Tuesday, September 16, 2008 3:00 AM

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The missing indexes DMVs are reset when the server starts. They can't be modified by a user.

One thing I would like to add is that the missing indexes DMVs should (like the Database Tuning Advisor) be taken as a suggestion and tested carefully before been applied. The missing indexes are less accurate than the DTA, as only single queries are considered when entries are added to that (the query optimiser adds the entries as it's optimising queries).

It doesn't take into account existing indexes, it doesn't compare with other similar suggestions already in the DMV and it doesn't considered clustered/nonclustered indexes.

They are very, very useful for index tuning, they just shouldn't be applies without consideration.

Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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Post #570022

SuperDBA-207096

Posted Tuesday, September 16, 2008 4:59 AM

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GilaMonster (9/16/2008)

They are very, very useful for index tuning, they just shouldn't be applies without consideration.

Good point! Remember every action has consequences, so be sure to test!

Post #570081

kevriley

Posted Tuesday, September 16, 2008 6:33 AM

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GilaMonster (9/16/2008)

It doesn't take into account existing indexes

Gail, can you explain what you mean ??

Kev

Post #570146

Charles Kincaid

Posted Tuesday, September 16, 2008 8:23 AM

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Good article. Great starting point. I one time saw a script that used this info to build the suggested indexes.

There is also some DMV about unused indexes. I'd love to see a set of scripts that would build the missing and deleted the unused.

ATB

Charles Kincaid

Post #570270

RBarryYoung

Posted Tuesday, September 16, 2008 8:24 AM

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Great article, I'm looking forward to using this.

-- RBarryYoung, (302)375-0451 blog: MovingSQL.com, Twitter: @RBarryYoung
Proactive Performance Solutions, Inc. "Performance is our middle name."

Post #570271

Marios Philippopoulos

Posted Tuesday, September 16, 2008 8:27 AM

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Gail already mentioned some of the caveats of the missing-index DMVs.

Here are a couple more:

(1) Because the data in the DMVs are kept in memory, they are at risk of being flushed from the cache if there is memory pressure. Therefore, the DMVs need to be polled regularly and stored in a database for later analysis. This is something Gail has mentioned before in one of the posts here.

(2) The DMVs are no substitute for a strategy of regular index defragmentation and statistics updating. The optimizer may make the wrong choices when it constructs the 'best' execution plans if indexes are defragmented and/or the stats is not up-to-date and accurate. This can cause "wrong" data to be deposited to the DMVs and therefore erroneous information.

I absolutely love the DMVs. They have opened a much-needed window into the internals of the database engine and have made DBA work all the more interesting. I use them all the time.

We just need to keep these limitations in mind as well.

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Post #570275

Marios Philippopoulos

Posted Tuesday, September 16, 2008 9:05 AM

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See this great link on the same topic:

Uncover Hidden Data to Optimize Application Performance:
http://msdn.microsoft.com/en-us/magazine/cc135978.aspx

__________________________________________________________________________________

Turbocharge Your Database Maintenance With Service Broker: Part 1
Real-Time Tracking of Tempdb Utilization Through Reporting Services
Monitoring Database Blocking Through SCOM 2007 Custom Rules and Alerts
Preparing for the Unthinkable - a Disaster/Recovery Implementation

Post #570331

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