Simple Parameterization and Trivial Plans—Part 4
How the SQL Server parser interacts with simple parameterization.
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Simple Parameterization and Trivial Plans—Part 3
The often contradictory information shown in execution plans about simple parameterization.
Simple Parameterization and Trivial Plans—Part 2
The quriky rules for data type assignment during simple parameterization.
Simple Parameterization and Trivial Plans—Part 1
Shell plans, plan stubs and how to cache only prepared plans (not ad-hoc).
Be Careful with LOBs and OPTION (RECOMPILE)
The parameter embedding optimization enabled by a RECOMPILE query hint doesn't always work to your advanatge when large objects are involved.
The Adaptive Join Threshold
How an adaptive join decides to use a batch mode hash join or row mode apply. Includes details of the threshold calculation.
Foreign Keys, Blocking, and Update Conflicts
Foreign key blocking under read committed snapshot isolation and related update conflicts under snapshot isolation.
Empty Parallel Zones in SQL Server Execution Plans
Why you can sometimes see two sequential Parallelism operators in SQL Server execution plans.
How Parallel Plans Start Up—Part 5
How additional parallel tasks cooperate to complete plan execution, including returning rows to the client.
How Parallel Plans Start Up—Part 4
Exchange synchronization, CXPACKET waits, and parallel task opening.
How Parallel Plans Start Up—Part 3
Starting the query scan, "early phases" processing, and starting the first parallel tasks.
How Parallel Plans Start Up—Part 2
Iterative execution, invisible plan performance profilers, and how the top-level query scan begins.
How Parallel Plans Start Up—Part 1
The role of the parent task (coordinator) in preparing a plan for parallel execution. Includes initializing each operator and adding hidden profilers to collect runtime performance data such as row count and elapsed time.
Incorrect Results with Parallel Eager Spools and Batch Mode
An incorrect results bug with batch mode hash joins and a parallel eager table spool used for Halloween Protection. Unfixed before SQL Server 2022.
Understanding Execution Plan Operator Timings
How SQL Server actual execution plan operator timings work, and why parallel row mode plan timings can be misleading.
SQL Server batch text hash and the sql_handle
Describes the structure of a sql_handle and explains how the SQL Server batch text hash component is calculated. Provides T-SQL functions to replicate the calculations.
Closest Match with Sort Rewinds
A SQL Server sort operator can replay its results, but only when the sort operates on at most one row. This article employs a sort to avoid a table spool in a query designed to find the closest match to a given value in a second table.
When Do SQL Server Sorts Rewind?
The rare circumstances when a SQL Server sort operator inside a nested loop can rewind (replay) cached results to avoid re-executing child plan operators.