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Curated SQL Posts

A Visual Explanation of Row Context in DAX

Published 2024-07-30 by Kevin Feasel

Marco Russo and Alberto Ferrari get visual:

Row context is the second fundamental concept in writing DAX code. In a previous article, we introduced the first concept – the filter context – using a visual approach. In this article, we rely on graphical visualization to describe a row context.

This article provides a different perspective on a topic already discussed in other row context articles: read them to get more insights about this important concept for DAX.

Click through for a great primer on the topic.

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Linux Memory Overcommit and PostgreSQL

Published 2024-07-30 by Kevin Feasel

Laurenz Albe shares a warning:

Linux tries to conserve memory resources. When you request a chunk of memory from the kernel, Linux does not immediately reserve that memory for you. All you get is a pointer and the promise that you can use the memory at the destination. The kernel allocates the memory only when you actually use it. That way, if you request 1MB of memory, but use only half of it, the other half is never allocated and is available for other processes (or the kernel page cache).

Overbooking is a concept that airlines all over the world have been using for a long time. They sell more seats than are actually in the plane. From experience, airlines know that some passengers don’t show up for the flight, so overbooking allows them to make more profit. By default, Linux does the same: it deals out (“commits”) more memory than is actually available in the machine, in the hope that not all processes will use all the memory they allocate. This memory overcommit is great for using resources efficiently, but it has one problem: what if all the flight passengers show up, that is, what if the processes actually use more memory than is available? After all, you cannot offer a computer process a refund or a free overnight hotel room.

Read on to learn more about memory overcommit and what you can do about it.

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Security Options in Microsoft Fabric Warehouses

Published 2024-07-30 by Kevin Feasel

Koen Verbeeck locks things down:

We are implementing a data analytics solution in Microsoft Fabric. A warehouse is used for the gold layer, and we want to give users access to the data. However, by sharing the warehouse, they can read all the data in all the tables. Some data is sensitive, and only users with the correct permissions should be able to view it. Is it possible to implement more granular access control to the data?

Read on for the answer, as well as an important note on how users might be able to circumvent your permissions settings.

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Microsoft Fabric GitHub Integration Security Considerations

Published 2024-07-30 by Kevin Feasel

Kevin Chant covers a bit of security:

I know the option to work with GitHub has got a lot of people excited. Which I why wanted to share my initial thoughts about security with you all. Because a lot of things have come to mind whilst testing this.

I want to highlight immediate implications and options before you all get too involved with testing. To make sure you test working with GitHub safely.

Plus, this post is really useful for those of you looking to test this in a regulated GitHub Enterprise environment. Because it will allow you to explain things to your GitHub administrators better, and/or forward them this post. To explain what you want to achieve.

Read on for Kevin’s thoughts on the matter.

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Optimistic Locking in Postgres

Published 2024-07-30 by Kevin Feasel

Semab Tariq explains how optimistic locking works in PostgreSQL:

Concurrency control in databases ensures that multiple transactions can occur simultaneously without causing data errors. It’s essential because, without it, two people updating the same information at the same time could lead to incorrect or lost data. There are different ways to manage this, including optimistic locking and pessimistic locking. Optimistic locking assumes that conflicts are rare and only checks for them when updating data. In contrast, pessimistic locking assumes conflicts are likely and locks data early to prevent issues. Optimistic locking allows for more concurrent transactions and better performance in systems with fewer conflicts.

Read on to learn more about it, including some patterns for best use and what to avoid.

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AutoML in Python with TPOT

Published 2024-07-29 by Kevin Feasel

Abid Ali Awan gives us a primer on TPOT:

AutoML is a tool designed for both technical and non-technical experts. It simplifies the process of training machine learning models. All you have to do is provide it with the dataset, and in return, it will provide you with the best-performing model for your use case. You don’t have to code for long hours or experiment with various techniques; it will do everything on its own for you.

In this tutorial, we will learn about AutoML and TPOT, a Python AutoML tool for building machine learning pipelines. We will also learn to build a machine learning classifier, save the model, and use it for model inference.

Click through to see an example of how to use the library.

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FabricRestClient and Long-Running Operations

Published 2024-07-29 by Kevin Feasel

Sandeep Pawar has a public service announcement:

I want to thank Michael Kovalsky for pointing out that FabricRestClient in Semantic Link supports (since v 0.7.5) Long Running Operation (LRO).

LRO support allows the client to wait for the request to process without being blocked. Without LRO support, you will get a 202 response code saying the request is being processed. You need to submit another request based on the url returned to get the result. With LRO support, FabricRestClient will wait 20s and give you the result back.

Click through to see what you’d need to do to enable it, as well as the benefit you can receive.

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Rounding Options in T-SQL

Published 2024-07-29 by Kevin Feasel

Rick Dobson talks rounding:

Please compare the SQL Server round function to banker’s rounding in T-SQL for converting decimal values to integer values. I seek a framework for assessing how closely banker’s rounding results versus SQL Server Round function results match the underlying decimal values. Please provide a couple of empirical comparisons with the framework to indicate which set of rounded values are closer to the underlying decimals and by how much.

Rick talks about what banker’s rounding is and shows how its results adhere more closely to the underlying distribution. Rick does show a user-defined function that generates a rounded number, but if you’re doing this with large enough amounts of data, using CLR and the System.Math.Round() function will likely give you better performance. Incidentally, this is also why if you write T-SQL code to round decimal numbers and .NET code to round numbers, your results may be a little different: T-SQL rounds to the nearest integer, whereas .NET uses banker’s rounding by default.

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Restoring a MySQL Table from Filesystem Backup

Published 2024-07-29 by Kevin Feasel

Chad Callihan recovers from a missing database backup:

There may be no worse feeling than needing a database backup and not having one. It ranks right up there with running a DELETE statement and missing the WHERE clause. God help you if you if you suffer both of those together. If you come across that situation with a MySQL database, you might be able to recover what you need.

Read on to see how. Even so, I’d be concerned about what happens if there are foreign key constraints involved.

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