LOB logical reads without LOB columns
LOB logical reads can be reported on a table with no LOB columns. This is caused by row overflow data (SLOBs).
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Seeking Without Indexes
Singleton seeks, range scan seeks, multiple seeks in one, and a seek on a heap with no indexes
Is it a Seek or a Scan?
Singleton seeks and seeks with range scans. Multiple seeking operations in a single SQL Server execution plan operator.
When is a Seek not a Seek?
SQL Server can perform multiple index seeking operations in a single Index Seek operator.
Beware Sneaky Reads with Unique Indexes
A side effect of the Split, Sort, and Collapse operators used to avoid false transient unique key violations.
Heaps of Trouble?
How a nested loops join with Eager Index Spools can be faster than a hash join.
Myth: SQL Server Caches a Serial Plan with Every Parallel Plan
SQL Server does not cache a separate serial version of a parallel plan.
The Case of the Missing Shared Locks
SQL Server contains an optimization that means row locks under read committed isolation can sometimes be safely skipped.
Sequence Tables
How to properly implement a custom Sequence Table facility, safe under high concurrency, and able to pre-allocate a range of values.
A Tale of Two Index Hints
A detailed look at the differences between the INDEX(0) and INDEX(1) SQL Server table hints.
Inside the Optimizer: Plan Costing
How the SQL Server query optimizer calculates plan operator costs. Adjusting the cost model with DBCC SETCPUWEIGHT and DBCC SETIOWEIGHT.
Sorting, Row Goals, and the TOP (100) Problem
The Top N Sort operator uses different implementations depending on the number of rows requested. For up to 100 rows it uses replacement selection and will never spill to tempdb.
Row Goals and Grouping
Why SQL Server will choose a Hash Match Flow Distinct operator when a row goal is present. Other options for grouping, and when they are chosen.
Inside the Optimizer: Row Goals In Depth
SQL Server does not always optimize to return the full result set. Various query features can introduce a "row goal", which aims to produce the first few rows quickly.
Viewing Another Session’s Temporary Table
Reading the contents of a local temporary table created in a different SQL Server session.
The Impact of Non‑Updating Updates
SQL Server optimizations for UPDATE statements that do not change data values. Covers logging, dirty pages, and avoiding the update completely.
Iterators, Query Plans, and Why They Run Backwards
How SQL Server row mode execution plans execute in detail.
Another Interesting MERGE Bug
A SQL Server bug with MERGE statements on table variables with an OUTPUT clause.