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Back in hospital

March 15, 2026

(Warning: This blog post is non-technical but purely personal. I write openly about my current health issues. This blog might be triggering for people who struggle with, or lost dear ones to, cancer and other similar diseases.) Time for an update in my leukemia diary. I had planned to write as soon as I was admitted to the hospital. I changed that plan a bit, for reasons I’ll get into later. But I am in hospital now, for a few days already. Awkward communication The last thing I had heard from my hematologist when I wrote the previous blog was…

Return to the diary

March 5, 2026

Hugo Kornelis

(Warning: This blog post is non-technical but purely personal. I write openly about my current health issues. This blog might be triggering for people who struggle with, or lost dear ones to, cancer and other similar diseases.) In September 2022, I was diagnosed with leukemia. I was treated with chemotherapy, I received a stem cell infusion, and then, after a long recovery period, I was clean and I could return to life before I got ill. I wrote about that extensively, in what I called my leukemia diary. The only thing in my life that still reminded me of my…

Optimized Locking part 2: Lock After Qualification

February 26, 2026

Hugo Kornelis

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SQL Server 2025 introduced Optimized Locking. Not one, but two features, sharing a single marketing name. Lock After Qualification (LAQ) One of these two features is Lock After Qualification (LAQ). This feature avoids the scenario where a delete or update is blocked by a locked row that would not qualify. But, like any good thing, there is a price. This video shows the feature, explains how it works, and shows some of the potentially undesired side effects. More of me? Was this useful to you? Do you want to learn more from me? You can click here to see an…

Video training update

February 22, 2026

Hugo Kornelis

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My training videos in the SQLServerFast Execution Plan Video Training are never just a done deal. Whenever there is new information to share, either because Microsoft adds new functionality, or because I discover something I did not know before, I go back and add this new information to the appropriate videos. Any such update always comes free of charge to those who bought access to the videos. Once you have access, you can watch these videos as often as you like. And you will always see the latest and greatest version! So it makes sense to stay updated on those…

Photo of Hugo Kornelis presenting at a conference

Precon, precon, precon

February 15, 2026

Hugo Kornelis

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If you read this blog, then it is very likely that you have an interest in execution plans. And that you want to increase your understanding of execution plans. A great way to really get to the next level is to attend a precon about execution plans, to get a full day of training on this topic. Another option is to purchase access to the SQLServerFast Execution Plan Video Training, currently over 20 hours of video with very extensive and in-depth training on execution plans. The best option is of course to combined the two: attend a precon, and get…

Storage structures 3 – Memory-optimized

February 13, 2026

Hugo Kornelis

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Update February 26: The maximum of 8 memory-optimized indexes per table was dropped in SQL Server 2017. After discussing traditional on-disk rowstore storage in part 1 and columnstores in part 2, it is now time to turn our eye towards memory-optimized storage structures in SQL Server. Memory-optimized storage was introduced in SQL Server 2014, as part of a project that was codenamed “Hekaton” and later renamed to in-memory OLTP. Whereas columnstore indexes were specifically targeted towards large scale analytical work, Hekaton and memory-optimized tables are specifically geared towards high volume OLTP workloads. By fully eliminating locks and latches, and using…

Optimized Locking part 1: Transaction ID Locking

February 12, 2026

Hugo Kornelis

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SQL Server 2025 introduced Optimized Locking. Not one, but two features, sharing a single marketing name. Transaction ID (TID) Locking One of these two features is Transaction ID (TID) Locking. Slated to end the memory waste of thousands of individual row locks, and the concurrency killer of lock escalation. What it is, how does it work, what are the limitations, and do we really get a free lunch? More of me? Was this useful to you? Do you want to learn more from me? You can click here to see an overview of my scheduled conference talks. If you attend…

T-SQL Tuesday 195 – Code that aged well

February 10, 2026

Hugo Kornelis

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It’s the second Tuesday of the month again. Time for T-SQL Tuesday, edition 195. This edition is hosted by Pat Wright, who wants to know whether our code aged well. The timing of that question could not have been any better for me, because I am right now working on an assignment related to a database system that I first worked for over 10 years ago! The database system I started working for the company in summer 2013. This was on employment, with a one-year contract. They used a SQL Server database to support their subscription administration and invoicing process.…

Rowgoals, part 3: When rowgoals backfire

February 2, 2026

Hugo Kornelis

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In part 1 of this mini-series, I explained what a rowgoal is and how it works to optimize a query with a TOP or FETCH expression. Part 2 then showed a few less obvious other cases where the optimizer might introduce rowgoals. In all cases so far, those rowgoals were beneficial. They helped the optimizer come up with the best execution plan for the number of rows requested. Things can go wrong! Unfortunately, there are cases where a plan that is optimized with a rowgoal turns out to be slower than without the rowgoal. The feature that is intended to…

Storage structures 2 – Columnstore

January 30, 2026

Hugo Kornelis

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Update February 4, 2026: I have updated this post with new information, about deleted bitmaps, and about the delete buffer for nonclustered columnstore indexes. Update February 5, 2025: Another update, fairly small in this case. Ordered columnstore indexes were introduced in SQL Server 2022. In the first part of this series, I described the storage structure and access patterns for SQL Server’s traditional storage structure: on-disk rowstore indexes (heaps and B-trees). Columnstore indexes were introduced in SQL Server 2012. In that version only nonclustered columnstore indexes were supported (so they stored a copy of the data in the included columns,…

Back in hospital

Return to the diary

Optimized Locking part 2: Lock After Qualification

Video training update

Precon, precon, precon

Storage structures 3 – Memory-optimized

Optimized Locking part 1: Transaction ID Locking

T-SQL Tuesday 195 – Code that aged well

Rowgoals, part 3: When rowgoals backfire

Storage structures 2 – Columnstore

The Beatles versus the Stones – the explanation

Back with a vengeance!

Can you trust your constraints?

Correcting my mistake

Going to Dublin

The Bounding Box, corrected version

NULL – The database’s black hole

The logic of three-valued logic

A Better Developer in 6 months? Deal!

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