Product has been added to your cart.

Indexing

  1. Home
  3. Indexing
    4. (Page 4)

[Video] Interpreting Missing Index Recommendations

Brent Ozar
Indexing, Videos
This week, we’re sharing Instant Replay videos from our training classes. Next up is Pinal Dave talking about missing index requests from the dynamic management views. It doesn’t matter whose script you use – they’re all built atop SQL Server’s missing-index DMVs, and they all have the same limitations. Treat the missing index requests the…
Read More

Management Studio Hides Missing Indexes From You.

Brent Ozar
Indexing
1 Comment
SQL Server Management Studio only shows you the first missing index recommendation in a plan. Not the best one. Not all of them. Just whichever one happens to show up first. Using the public Stack Overflow database, I’ll run a simple query: Transact-SQL SELECT c.CreationDate, c.Score, c.Text, p.Title, p.PostTypeId FROM dbo.Users me INNER JOIN dbo.Comments c…
Read More

Does It Matter Which Field Goes First in an Index?

Brent Ozar
Indexing
9 Comments
Let’s take the dbo.Users table from the Stack Overflow database, which holds exactly what you think it holds – the list of users: StackOverflow.dbo.Users Say I want to count up all of the people with 1 reputation point: Transact-SQL SELECT COUNT(*) FROM dbo.Users WHERE Reputation = 1; 1 SELECT COUNT(*) FROM dbo.Users WHERE Reputation =…
Read More

Can Non-SARGable Predicates Ever Seek?

Erik Darling
Development, Indexing
4 Comments
Cheating At Candy Crush The short answer is that yes, they can. But only with a little extra preparation. Before I show you what I mean, we should probably define what’s not SARGable in general. Wrapping columns in functions: ISNULL, COALESCE, LEFT, RIGHT, YEAR, etc. Evaluating predicates against things indexes don’t track: DATEDIFF(YEAR, a_col, b_col),…
Read More

Mysterious Forwarded Records

Erik Darling
Indexing
5 Comments
Thinking Of You When people think about Heaps and the problems they can cause, they don’t often think of temp tables and table variables as Heaps. Of course, without a clustered index, any table is a Heap. This isn’t an argument for or against indexing temp tables, but while working with a client we came…
Read More

Trivial Plans, Simple Parameterization and Check Constraints

Erik Darling
Execution Plans, Indexing
Trivial Plans Are Weird They’re the optimizer’s “Yes, Dear”.  The thing is, sometimes “Yes, Dear” can miss some important details. Cost based decisions about operators Potential index improvements Contradiction detection for check constraints Simple parameterization, according to… uh… Official Microsoft documentation? Can only occur in a Trivial Plan. Which makes sense. Simple parameterization is considered…
Read More

Where Clustered Index Keys Dare

Erik Darling
Indexing, SQL Server
5 Comments
Colonel Clustered We’ve blogged a couple times about how clustered index key columns get stored in your nonclustered indexes: here and here. But where they get stored is a matter of weird SQL trivia. You see, it depends on how you define your nonclustered index. “It Depends” We all scream for dependencies! Hooray! If you…
Read More

When Query Plans Lie Part 2

Erik Darling
Execution Plans, Indexing, SQL Server
Getting Weirder In Part 1, we looked at how query plans can tell us little lies. Now we’re going to look at how those little lies can turn into bigger lies. Adding An Index Right now, this is our query: Transact-SQL SELECT u.UpVotes, u.DownVotes FROM dbo.Users AS u WHERE u.Reputation >= 100000; 123 SELECT u.UpVotes,…
Read More

Hey, That’s Not My Sort!

Erik Darling
Execution Plans, Indexing
5 Comments
Understand Your Plan Mr. Optimizer does the rock n roll hoochie koo with Mrs. Optimizer, c. 1953. When reading query plans, you may sometimes see a sort when you didn’t explicitly ask for data to be sorted. Sometimes they show up to support order-preserving operators like stream aggregates, merge joins, or segments. Other times, they…
Read More

The Many Mysteries of Merge Joins

Erik Darling
Execution Plans, Indexing
5 Comments
Not A Single Picture Of A Zipper Image humbly borrowed from https://70srichard.wordpress.com/2014/12/17/beverly-hills-cop/ There are some interesting things about Merge Joins, and Merge Join plans that I figured I’d blog about. Merge joins have at least one interesting attribute, and may add some weird stuff to your query plans. It’s not that I think they’re bad,…
Read More

Missing Index Impact and Join Type

Erik Darling
Indexing
8 Comments
Just Another Way No matter how you delve into missing index requests — whether it’s the plan level, DMV analysis, or (forgive me for saying it), DTA, the requests will generally be the same. They’ll prioritize equality predicates, the columns may or not may be in the right order, the columns may or may not…
Read More
Menu
{"cart_token":"","hash":"","cart_data":""}