Read Gather Streams and other parallel exchanges, inspect rows per thread and spill evidence, and relate exchange waits to actual work.
Operator Costs in an Execution Plan: Read Them Without Being Fooled
Interpret operator costs as estimates, compare actual rows and runtime evidence, and find expensive work without trusting plan percentages.
How to Know If Index is Forced on Query? – Interview Question of the Week #246
Question: How to Know If Index is Forced on Query?
Answer: Let me tell you a brief story so you understand the context of the question.
NonParallelPlanReason: Why a Query Refuses to Go Parallel
Read NonParallelPlanReason in actual and cached plans, then check MAXDOP, scalar functions, table variables, and query cost.
Long-Running Query for Demonstrations You Can Control
A long-running query for demonstrations has to run long enough to watch and stop when you say. This post builds one from a counting table, shows how its run time grows with the row count and explains how to watch and stop it. It also compares it with WAITFOR DELAY.
Delete the Wrong Row: A Cheap Answer That Passes the Test
A cheap answer to the multiple table delete puzzle reads only 6 pages and passes the check. It can still delete the wrong row. This post shows the answer, asks you to find the row it removes by mistake, and fixes it with a delete that costs 5 reads.
Filtered Statistics: Fixing Estimates for Skewed Data
Use filtered statistics to describe skewed customer values, inspect histograms, and test estimates under literal and parameterized queries.