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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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Rebuilding Indexes Can Slow Queries Down

Today, Jonathan Kehayias wrote about how fragmentation impacts execution plans. I’m really into performance tuning, so I read the post carefully, really interested to see how it impacted query runtime. You should read it too – it’s a great post with a solid demo. But oddly, he didn’t mention the query speeds. I thought that was…
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Partition Level Locking: Explanations From Outer Space

It’s not that I don’t like partitioning It’s just that most of my time talking about it is convincing people not to use it. They always wanna use it for the wrong reasons, and I can sort of understand why. Microsoft says you can partition for performance. Partitioning large tables or indexes can have the…
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Brent Ozar reading

New System Stored Procedures in SQL Server 2017

Got a few new stored procs for columnstore indexes: sp_add_columnstore_column_dictionary – input params for @table_id, @column_id sp_is_columnstore_column_dictionary_enabled – as above, plus output param for @is_enabled bit sp_remove_columnstore_column_dictionary – input params for @table_id, @column_id And a couple for snapshot views (which appear to be related to the new snapshot messages in sys.messages) sp_refresh_single_snapshot_view – input param for @view_name…
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Key Lookups and ColumnStore Indexes

Beavis v. Butthead I was a bit surprised that this was a possibility with ColumnStore indexes, since “keys” aren’t really their strong point, but since we’re now able to have both clustered ColumnStore indexes alongside row store nonclustered indexes AND nonclustered ColumnStore indexes on tables with row store clustered indexes, this kind of stuff should…
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Optional Parameters and Missing Index Requests

That’s when it all gets blown away At one point or another in everyone’s SQL-querying career, they end up writing a query that goes something like this: Transact-SQL SELECT something FROM stuff WHERE (@thing1 is NULL or whatever = @thing1) AND ... 1234 SELECT somethingFROM stuffWHERE (@thing1 is NULL or whatever = @thing1)AND ... These…
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How Much Can One Column Change A Query Plan? Part 2

What happened in Part 1? Join Elimination, naturally. Until the end. My copy of the Stack Overflow database doesn’t have a single foreign key in it, anywhere. If we go down the rabbit hole a couple steps, we end up at a very quotable place, with Rob Farley. 2. Duplicated rows Not necessarily duplicated completely,…
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ColumnStore Indexes: Rowgroup Elimination and Parameter Sniffing In Stored Procedures

Yazoo Over on his blog, fellow Query Plan aficionado Joe Obbish has a Great Post, Brent® about query patterns that qualify for Rowgroup Elimination. This is really important to performance! It allows scans to skip over stuff it doesn’t need, like skipping over the dialog in, uh… movies with really good fight scenes. Car chases?…
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How to Drop All Your Indexes – Fast

Sometimes I need to reset stuff during performance training classes. I know some of you teach classes, too, and some of you just like doing crazy stuff. So here you go, a stored procedure to lose weight fast: DropIndexes for SQL Server 2016 & Newer Transact-SQL CREATE OR ALTER PROCEDURE [dbo].[DropIndexes] @SchemaName NVARCHAR(255) = 'dbo',…
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Five Mistakes Performance Tuners Make

There’s no Top in the title And that’s because a TOP without an ORDER BY is non-deterministic, and you’ll get yelled at on the internet for doing that. This is just a short collection of things that I’ve done in the past, and still find people doing today when troubleshooting performance. Sure, this list could…
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Locking When There’s Nothing To Lock

Demo Day We use StackOverflow for demos a lot. For all the reasons Brent mentions in his Great Post, Brent©, it’s pretty awesome. Where things get tricky is with locking demos. Sometimes the modifications can take a long time. This may be by design if you need to show long-held locks by sessions that aren’t…
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