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Cardinality Estimation Bug with Lookups Estimated row counts on Key or RID Lookups where a filtering predicate is app...

Why Doesn’t Partition Elimination Work? Given a partitioned table and a simple SELECT query that compares the partitio...

Compute Scalars, Expressions and Execution Plan Performance The humble Compute Scalar is one of the least well-underst...

Deletes that Split Pages and Forwarded Ghosts Can DELETE operations cause pages to split? Yes. It sounds counter-int...

Temporary Table Caching Explained SQL Server (since 2005) caches temporary tables and table variables referenced in ...

Temporary Table Caching in Stored Procedures Introduction Ask anyone what the primary advantage of temporary tables ...

Parallel Execution Plans Suck Summary : A deep dive into SQL Server parallelism, and a potential performance problem wi...

Query Optimizer Deep Dive - Part 4 This is the final part in a series of posts based on the content of the Query Optim...

Query Optimizer Deep Dive – Part 3 This is the third in a series of posts based on the content of the Query Optimizer ...

Query Optimizer Deep Dive – Part 2 This is the second in a series of posts based on the content of the Query Optimizer...

Query Optimizer Deep Dive - Part 1 This is the first in a series of posts based on the content of the Query Optimizer ...

Fun with Scalar and Vector Aggregates There are interesting things to be learned from even the simplest queries. For e...

Dynamic Seeks and Hidden Implicit Conversions A LIKE predicate with only a trailing wildcard can usually use an index...

Forcing a Parallel Query Execution Plan This article is for SQL Server developers who have experienced the special kind...

SQL Server Optimizer Bug with JOIN and GROUP BY I came across a SQL Server optimizer bug recently that made me wonder h...

Is Distinct Aggregation Still Considered Harmful? Back in 2008, Marc Friedman of the SQL Server Query Processor Team wr...

Finding the Statistics Used to Compile an Execution Plan In this post, I show you how to determine the statistics objec...

Can a SELECT query cause page splits? The SQL Server documentation has this to say about page splits : When a new row...

SQL Server, Seeks, and Binary Search The following table summarizes the results from my last two articles, Enforcing Un...

Avoiding Uniqueness for Performance In my last post, Enforcing Uniqueness for Performance , I showed how using a unique...

Enforcing Uniqueness for Performance A little while back, I posted a short series on seeks and scans: When is a Seek ...

Join Performance, Implicit Conversions, and Residuals Introduction You probably already know that it’...

Bitmap Magic (or… how SQL Server uses bitmap filters) Question Can a parallel query use less CPU than the same serial...

Undocumented Query Plans: The ANY Aggregate As usual, here’s a sample table: CREATE TABLE #Example ( pk numeri...

Undocumented Query Plans: Equality Comparisons The diagram below shows two data sets, with differences highlighted: T...