How to
Deploy at Low Priority
Deploy SQL Server schema changes without a maintenance window using a WAIT_AT_LOW_PRIORITY-inspired loop that checks for SCH-S locks and bails out with GOTO.
Notes from a TSQL trench
Database stuff,
with a side of memes.
Long-form notes on TSQL performance, Extended Events, Query Store and the tooling around them. Written from the trenches, not the slide deck.
Featured
Opinion
Why is fn_xe_file_target_read_file the worst SQL function?
Why SQL Server's fn_xe_file_target_read_file is so frustrating: an nvarchar(max) return type, broken timestamp filtering, and no efficient way to find rollover files.
Tools
SSMS: Layout, Options and Hotkeys
How I configure SQL Server Management Studio: window layout, the Options settings that matter, essential hotkeys, and small productivity wins for DBAs.
Deep Dive
Async stats update causing blocking
How lock partitioning causes async stats updates to block during online index rebuilds with WAIT_AT_LOW_PRIORITY - full repro and the SQL Server 2022 fix.
How to
Default event_file path for Extended Events
SQL Server stores event_file data in the error log folder when no full path is given. Steps to find the current location and change it, on Windows and in Docker.
Investigation
Unexpected Blocking during the Indexed View Creation
Creating the clustered index on an Indexed View blocked unrelated queries even under RCSI. The cause was Enterprise view matching, fixable with EXPAND VIEWS.
Investigation
What is causing my constraint to be untrusted?
A CHECK or FOREIGN KEY constraint keeps reverting to untrusted overnight. Here is how to catch the BULK INSERT or bcp process doing it, with Extended Events.
Deep Dive
How Scalar Functions Prevent Parallelism
Scalar UDFs silently force your query to run serially, killing parallelism. Even a reference through a view, computed column, or check constraint does it.
How to
SQL Server Module Signing for Secure Cross-Database Access
How to set up module signing with certificates in SQL Server for cross-database access - without ownership chaining. Complete walkthrough with diagram and follow-along example.
Opinion
Why my way of writing SQL is superior
Are semicolons required in SQL Server statements? Plus leading commas, single-letter aliases, and the other TSQL formatting choices I refuse to budge on.
How to
Query Hash and Query Plan Hash Mapping
DMVs and Query Store store the query hash as binary(8), but Extended Events shows a number, and the two refuse to match. Here's how to map between them.
Deep Dive
KEEP PLAN Demystified
The KEEP PLAN hint is supposed to relax recompilation thresholds, but the docs are vague. I test it against permanent and temp table statistics thresholds.
Investigation
How to audit data modifications with surgical precision
Combine an AFTER UPDATE trigger with Extended Events to surgically audit only the data changes you care about, cutting through thousands of modifications.
Investigation
IS Lock in RCSI Enabled Database
An IS lock appeared in a deadlock report on a database running RCSI - which shouldn't take shared locks. The culprit turned out to be an Indexed View.
Deep Dive
Query Store default settings
Query Store defaults aren't exactly what the docs say. This post finds the real values using Extended Events and explains what Auto capture mode actually means.
How to
Investigating Errors With Extended Events
Track down SQL Server errors using Extended Events. Capture the full calling stack, parse it with TSQL, and pinpoint exactly where failures happen.
Latest posts
Finding and Triaging Scalar UDFs Across Your Environment
You've learned why Scalar UDFs are slow and how to remove them. The last question: where do you even start? Here's how I triage them across a whole environment.
Everything by voidtools: Instant File Search on Windows
Another productivity tool in my toolbox that I use daily. This time it's about file search. Everything will help you find... well, everything.
Unexpected Blocking during the Indexed View Creation
Here are the chronicles of my struggles to add a large Clustered index to a View without causing an outage.
Greenshot: Region Capture, Annotation and Obfuscation
Print Screen and Paint never cut it for me. Greenshot did: precise region capture, a real annotation editor, obfuscation, and one-key sharing. Here's the tour.
Fixing Scalar UDFs: SCHEMABINDING, Inlining and ITVF Rewrites
Nuke them from orbit, or inline them. The practical ways to neutralize Scalar UDF performance pain, from a free SCHEMABINDING win to a full ITVF rewrite.
What's in a name? (T-SQL Tuesday #152)
My T-SQL Tuesday rant: an app that connects as '.Net SqlClient Data Provider' turns debugging into a manhunt. Please, name your apps.
Measuring the Scalar UDF Performance Cost
A Scalar function that does literally nothing still runs over 20 times slower. Here is the proof, measured four different ways.