Primary Key vs. Clustered Index

In today’s blog posting I want to talk about a very important topic in SQL Server that always confuses people when they first work with SQL Server. It is about the difference between the Primary Key constraint and the Clustered Index. What is a Primary Key? Let’s talk first about ...

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Heap Tables and %%lockres%%

In today’s blog posting I want to show you a undocumented function in SQL Server, and how you can use that function to find out on which pages records are stored. %%lockres%% The undocumented function that I want to show you today is called %%lockres%% and has to do with ...

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Why the Query Hint NOLOCK is a bad idea

A few weeks ago I have presented my Performance Tuning Workshop in Utrecht/Netherlands. On the 3rd day – the most intensive one, where I cover Locking, Blocking, Deadlocking, Latching, Spinlocking – we have also talked about the NOLOCK query hint. Some people always refer to the NOLOCK query hint as ...

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Is a Index Scan always a Index Scan?

A few weeks ago, someone posted an interesting question on Twitter: Q: While watching a Summit14 recording, unanswered by speaker: Is there a way to tell how much of index is scanned with a NC scan operator? One of the answers to this question was that a Non-Clustered Index Scan ...

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