Bonfire of the vanities

“UPDATE, INSERT, and DELETE are not normally processed in parallel”

Years ago, when troubleshooting performance, I stumbled across this Microsoft documentation on parallel query processing that says: Certain types of statements cannot be processed in parallel unless they contain clauses, however. For example, UPDATE, INSERT, and DELETE are not normally processed in parallel even if the related query meets the criteria. But if the UPDATE…
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[Video] Watch Brent Tune Queries

Ever wonder somebody else does it? Watch over my shoulder as I spend 9 minutes in PowerPoint explaining the big picture, and then about 40 minutes working on this stored procedure in the StackOverflow2013 database: If you enjoy that, the Watch Brent Tune Queries page has another video and other query examples. Enjoy!
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How to Think Like the Engine: When a Seek Isn’t

In our last episode, I introduced the concept of scan predicates: execution plan operations that weren’t able to seek directly to the rows they needed. Let’s take another query: Transact-SQL DropIndexes; GO CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); GO SELECT Id FROM dbo.Users WHERE LastAccessDate > '1800/01/01' AND DisplayName = N'Brent Ozar'; GO…
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How to Think Like the Engine: Index Column Order Matters a LOT.

We’ve been working with the clustered index of the Users table, which is on the Identity column – starts at 1 and goes up to a bajillion: And in a recent episode, we added a wider nonclustered index on LastAccessDate, Id, DisplayName, and Age: Transact-SQL CREATE INDEX IX_LastAccessDate_Id_DisplayName_Age ON dbo.Users(LastAccessDate, Id, DisplayName, Age); GO 123…
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How to Think Like the SQL Server Engine: What’s the Tipping Point?

In our last episode, I’d expanded our query to include DisplayName and Age – two columns that weren’t in our nonclustered index: Transact-SQL SELECT LastAccessDate, Id, DisplayName, Age FROM dbo.Users WHERE LastAccessDate > '2018-09-02 04:00' ORDER BY LastAccessDate; 1234 SELECT LastAccessDate, Id, DisplayName, Age  FROM dbo.Users  WHERE LastAccessDate > '2018-09-02 04:00'  ORDER BY LastAccessDate; So as a result,…
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