Indexing

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Mysterious Forwarded Records

Indexing
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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…
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Trivial Plans, Simple Parameterization and Check Constraints

Execution Plans, Indexing
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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…
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Where Clustered Index Keys Dare

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…
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When Query Plans Lie Part 2

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,…
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Hey, That’s Not My Sort!

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…
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The Many Mysteries of Merge Joins

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,…
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Missing Index Impact and Join Type

Indexing
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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…
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Memory Grants: SQL Server’s Other Public Toilet

Sharing Is Caring When everything is going well, and queries are behaving responsibly, one need hardly think about memory grants. The problem becomes itself when queries start to over and under estimate their practical needs. Second Hand Emotion Queries ask for memory to do stuff. Memory is a shared resource. What kind of stuff? Well, usually…
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Functions Can Still Use Indexes, Kinda.

This sentence gets repeated a lot. You know the one: “Functions prevent the use of indexes.” Well, knowing you, it’s probably just your indexes. I’ve seen your indexes. Functions can use indexes, but even so, that doesn’t mean that they’re going to perform as well as queries without functions. Which Indexes? In the SUPERUSER database (yeah, I know, I’m…
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Computed Columns: Reversing Data For Easier Searching

During Training We were talking about computed columns, and one of our students mentioned that he uses computed columns that run the REVERSE() function on a column for easier back-searching. What’s back-searching? It’s a word I just made up. The easiest example to think about and demo is Social Security Numbers. One security requirement is…
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