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Day: January 30, 2025

Kernel Methods in Python

Published 2025-01-30 by Kevin Feasel

Matthew Mayo does a bit of kernel work:

Kernel methods are a powerful class of machine learning algorithm that allow us to perform complex, non-linear transformations of data without explicitly computing the transformed feature space. These methods are particularly useful when dealing with high-dimensional data or when the relationship between features is non-linear.

Kernel methods rely on the concept of a kernel function, which computes the dot product of two vectors in a transformed feature space without explicitly performing the transformation. This is known as the kernel trick. The kernel trick allows us to work in high-dimensional spaces efficiently, making it possible to solve complex problems that would be computationally infeasible otherwise.

Read on for the pros and cons of kernel methods and a pair of techniques that use them.

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The Ephemeral Nature of Index Rebuilds on RCSI and ADR

Published 2025-01-30 by Kevin Feasel

Brent Ozar lays out an argument:

Accelerated Database Recovery (ADR) is a database-level feature that makes transaction rollbacks nearly instantaneous. Here’s how it works.

Without ADR, when you update a row, SQL Server copies the old values into the transaction log and updates the row in-place. If you roll that transaction back, SQL Server has to fetch the old values from the transaction log, then apply them to the row in-place. The more rows you’ve affected, the longer your transaction will take.

With ADR, SQL Server writes a new version of the row inside the table, leaving the old version in place as well.

Because you’re a smart cookie, you immediately recognize that storing multiple versions of a row inside the same table is going to cause a storage problem: we’re going to be boosting the size of our table, quickly. However, the problem’s even bigger than that, and it starts right from the beginning when we load the data.

This was an interesting analysis, looking at table growth with ADR + RCSI, with ADR or RCSI alone, and with neither feature. Given that I’m all-in on RCSI, this is particularly interesting to me. And if you want to dig really deeply into index maintenance, Jeff Moden has a fantastic set of presentations, which TriPASS recorded in 2021: GUIDs vs Fragmentation and LOB data. These two presentations help provide sound footing for deciding under what circumstances it makes sense to rebuild an index, and noting that (unless you’re Brent), the answer is probably “less often than you’d think.”

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Case-Sensitive Elements in SQL Server Integration Services

Published 2025-01-30 by Kevin Feasel

Andy Brownsword has a list:

Case sensitivity in data can trip us up unknowingly and Integration Services is no exception. Depending on the components we’re using we may notice different behaviour.

Without understanding the way case sensitivity is treated within SSIS packages, we may see unexpected results with string comparisons.

Let’s clear things up and dive into a few examples to see when they behave differently.

Click through for three examples. One more that I’d add is Script components, which are C# or VB. Both of the languages are case sensitive, and string comparison in .NET is case sensitive unless you set StringComparison to one of the options that ignore case.

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