An Indexed View Bug with Scalar Aggregates
Details of a SQL Server bug that can render an indexed view incorrect.
Articles
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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.
Data Modifications under Read Committed Snapshot Isolation
Why and when UPDATE and DELETE statements acquire locks under RCSI.
Read Committed Snapshot Isolation
The detailed behaviour of RCSI compared with locking read committed isolation, including subtle aspects to be aware of.
The Read Committed Isolation Level
The logical and physical guarantees provided by read committed isolation.
The Repeatable Read Isolation Level
The guarantees provided by the repeatable read isolation level, including some allowed behaviours you might find surprising.
Cardinality Estimation for Disjunctive (OR) Predicates
The cardinality estimation formulas for multiple OR predicates in SQL Server 2014 and later (using the 'default' cardinality estimator).
The Serializable Isolation Level
Guarantees provided by the strongest transaction isolation level and what they mean in practice.
The ACID Properties of Statements & Transactions
Concurrency considerations and the practical meaning of each component of the ACID acronym in a SQL Server context.