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Curated SQL Posts

Data Modification with Synapse Link for SQL Server 2022

Published 2022-08-31 by Kevin Feasel

Kevin Chant changes some data:

In this post I want to cover some things that happen internally when you do updates and deletes with Azure Synapse Link for SQL Server 2022 whilst it is running.

Because recently somebody asked if Azure Synapse Link for SQL Server 2022 captures updates and deletes after they had read a previous post. Where I covered my initial tests for Azure Synapse Link for SQL Server 2022.

Anyway, short answer is that Azure Synapse Link for SQL Server 2022 captures updates and deletes. In this post I will go into more detail about some of the things that appear to happen along the way.

Click through for Kevin’s tests and what the results look like.

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Azure Synapse Analytics August 2022 Updates

Published 2022-08-31 by Kevin Feasel

Ryan Majidimehr has a changelog for us:

Full support for MLflow

MLflow is a platform for managing the machine learning lifecycle and streamline machine learning development, including tracking experiments, packaging code into reproducible runs, and sharing and deploying models. We are very happy to announce that SynapseML models now integrates with MLflow with full support for saving, loading, deployment, and autologging!

To learn more, read MLflow in SynapseML getting started guide and SynapseML Autologging.

There are quite a few changes on this list, so they’ve definitely been busy.

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The SQL ConstantCare Population Report

Published 2022-08-31 by Kevin Feasel

Brent Ozar surveys the SQL Server landscape:

Ever wonder how fast people are adopting new versions of SQL Server, or what’s “normal” out there for SQL Server adoption rates, hardware sizes, or numbers of databases? Let’s find out in the summer 2022 version of our SQL ConstantCare® population report.

Out of the 3,151 servers sending in data recently, the most popular version of SQL Server is still 2016:

Every time I link to this, I say the same two things: one, that it’s important to keep in mind that this is necessarily a biased sample (in that it includes the subset of organizations which has people who are familiar with Brent’s work, spends enough money to get ConstantCare support, and has a need for this support); and two, that I appreciate this sample. Yes, it’s biased and not necessarily indicative of the broader market but it’s also useful information, especially seeing trends over time.

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Understanding Write-Ahead Logging

Published 2022-08-30 by Kevin Feasel

Kevin Sookocheff explains how write-ahead logging protects data in databases:

A central tenet of databases is that any committed data survives a crash or a failure. Write-ahead logging is a fundamental primitive that ensures all changes to data are first written safely to stable storage before being applied. Coupling that with some careful use of sequence numbers and we can guarantee that changes made to a database can survive system crashes.

This is a core feature in pretty much every relational database and Kevin dives into how one of the key algorithms behind it works.

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KQL BETWEEN

Published 2022-08-30 by Kevin Feasel

Robert Cain proves it’s not the end of the line in his KQL series:

It’s not uncommon to want to use a range of values when creating a Kusto query. This might be a range of numeric values, or perhaps a range of dates.

Kusto provides this ability using the between operator. In this post we’ll see how to use it when authoring your Kusto queries.

Click through to see how you can use between as well as logical alterations such as not between.

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RELATED() and RELATEDTABLE() in DAX

Published 2022-08-30 by Kevin Feasel

Alberto Ferrari and Marco Russo add some context:

RELATED is one of the most commonly used DAX functions. You use RELATED when you are scanning a table, and within that row context you want to access rows in related tables. RELATEDTABLE is the companion of RELATED, and it is used to traverse relationships in the opposite direction. When learning DAX, it is easy to get confused and use RELATED when it is not necessary, or to forget about RELATEDTABLE. In this article, we describe the most common uses of the two functions, along with common misperceptions.

Click through to learn more about these two functions.

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DAX EVALUATEANDLOG() Function Outputs

Published 2022-08-30 by Kevin Feasel

Jeffrey Wang continues a series on EVALUATEANDLOG():

Last week, we learned how to interpret the output of the EvaluateAndLog function of scalar expressions. Albeit interesting, the new function would be much less useful if it could only return scalar values. After all, Power BI users can always define a scalar expression as a measure and then study its values in various contexts. The real power of EvaluateAndLog is that it can also wrap around any table expressions, the output of which was much harder to visualize until now.

This function exposes a lot of information, as you can see in the post.

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NESTING_TRANSACTION_FULL Latches

Published 2022-08-30 by Kevin Feasel

Paul White dives into latch contention:

This design has its roots in SQL Server 7, where read-only query parallelism was introduced. SQL Server 2000 built on this with parallel index builds, which for the first time allowed multiple threads to cooperate to change a persistent database structure. Many improvements have followed since then, but the fundamental parent-child transaction design remains today.

Though lightweight, a latch can become a point of contention when requested sufficiently frequently in incompatible modes by many different threads. Some contention on shared resources is to be expected; it becomes a problem when latch waits start to affect CPU utilisation and throughput.

Read the whole thing, as Paul dives into the latch design, provides an alternative design, and tests the alternative.

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Getting Status of Power BI Enhanced Refreshes

Published 2022-08-30 by Kevin Feasel

Chris Webb wants to know the situation, STAT:

So far in this series (see part 1, part 2 and part 3) I’ve looked at how you can create a Power Automate custom connector that uses the Power BI Enhanced Refresh API to kick off a dataset refresh. That’s only half the story though: once the refresh has been started you need to know if it has finished and, if so, whether it finished successfully or not. In this post I’ll show how to do this.

Read on to see how.

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