A deadlock in SQL Server is two sessions each holding what the other needs. I caused one on purpose and read error 1205. Why it is not the same as blocking, who gets killed, and the boring fix that works.
Overlapping Indexes With INCLUDE Columns: Merging Them Safely
Find overlapping indexes, compare ordered keys and INCLUDE lists, merge coverage carefully, and review usage before removing either index.
Why Queries Recompile
Why queries recompile becomes clearer when you capture Extended Events causes and check schema changes, statistics, SET options, and temp tables.
Query Store Hints: Fixing a Query Without Touching Its Code
Apply query store hints to a vendor query without code changes, verify failures and plan behavior, then clear the hint after the real fix.
Reading Pending I/O Requests During a Storage Slowdown
Sample pending I/O requests during PAGEIOLATCH or WRITELOG stalls, map each request to a file, and share timed evidence.
Finding Which Database Uses the Most CPU on a Shared Instance
Find which database uses the most CPU from cached query stats and plan attributes, then use Query Store for restart-safe history.
QUERY_OPTIMIZER_HOTFIXES: Turning On Optimizer Fixes per Database
A vendor says to turn on optimizer hotfixes. Here is how I check the setting, try it on one statement, and restore it.