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Improving the Top Based Pre-2012 Median Solution

Avoiding large memory grants and excessive scalar computations.

Improving the Pre-2012 Row Numbering Median Solution

Analyzing the cause of lower than expected performance and applying a correction.

Locking and Performance

The type and number of locks acquired and released during query execution can have a surprisingly large impact on performance, even if no waiting or blocking occurs.

Calculating the Median with a Dynamic Cursor

A fast way to compute single and grouped medians using a dynamic T-SQL cursor.

Internals of the Seven SQL Server Sorts—Part 2

SQL Server sort internals, including in-memory sorts and two new classes specific to In-Memory OLTP.

Internals of the Seven SQL Server Sorts—Part 1

The first four of the seven SQL Server sorts described in detail.

The Read Uncommitted Isolation Level

The guarantees provided by the weakest of the standard transaction isolation levels. Includes examples of less well-known concurrency effects.

An Indexed View Bug with Scalar Aggregates

Details of a SQL Server bug that can render an indexed view incorrect.

Indexed View Maintenance in SQL Server Execution Plans

How SQL Server maintains indexed views as the underlying data changes.

Allocation Ordered Scans

How SQL Server allocation ordered scans work in detail, when they can and can't be used, and how to disable them (almost) completely.

Performance Tuning the Whole Query Plan

Thinking laterally to find a better algorithm rather than tuning individual SQL Server execution plan operators.

Avoiding Sorts with Merge Join Concatenation

How merge concatenation can be used to avoid sorting, if you know enough about the SQL Server execution engine.

Rewriting Queries to Improve Performance

Though SQL is a declarative language, expressing queries differently can dramatically change execution plans.

The 2008 R2 Bug Fix That Breaks RCSI

Details of a regression in a deadlock fix.

A Subquery Cardinality Estimation Bug

A SQL Server semi join cardinality estimation bug where predicates pushed beyond a UNION ALL are missed.

SQL Server Isolation Levels: The Series

Index to my series on concurrency, the ACID properties of statements and transactions, and isolation levels in SQL Server.

The Snapshot Isolation Level

Guarantees provided by the SQL Server snapshot isolation level and some of its surprising behaviours.

An Unexpected Side-Effect of Adding a Filtered Index

Adding a filtered index can have surprising side-effects on existing queries, even where it seems the new filtered index is completely unrelated.