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Day: July 19, 2019

Building an Image Classifier with PyTorch

Published 2019-07-19 by Kevin Feasel

Rogier van der Geer shows how you can use PyTorch to build out a Convolutional Neural Network for image classification:

The tool that we are going to use to make a classifier is called a convolutional neural network, or CNN. You can find a great explanation of what these are right here on wikipedia.

But we are not going to fully train one ourselves: that would take way more time than I would be willing to spend. Instead, we are going to do transfer learning, where we take a pre-trained CNN and replace only the last layer by a layer of our own. Then we only need to train that single layer, as all the other layers already have weights that are quite sensible. Here we exploit the fact that the images we are interested in have a lot of the same properties as those images that the original network was trained on. You can find a great explanation of transfer learning here.

Read on for a detailed example.

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xgboost and Small Numbers of Subtrees

Published 2019-07-19 by Kevin Feasel

John Mount covers an interesting issue you can run into when using xgboost:

While reading Dr. Nina Zumel’s excellent note on bias in common ensemble methods, I ran the examples to see the effects she described (and I think it is very important that she is establishing the issue, prior to discussing mitigation).
In doing that I ran into one more avoidable but strange issue in using xgboost: when run for a small number of rounds it at first appears that xgboost doesn’t get the unconditional average or grand average right (let alone the conditional averages Nina was working with)!

It’s not something you’ll hit very often, but if you’re trying xgboost against a small enough data set with few enough rounds, it is something to keep in mind.

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Using AZCopy for SQL Backups

Published 2019-07-19 by Kevin Feasel

John McCormack shows how you can use AZCopy to move SQL Server backups into Azure Storage:

AZCopy is a useful command line utility for automating the copying of files and folders to Azure Storage Account containers. Specifically, I use AZCopy for SQL Backups but you can use AZCopy for copying most types of files to and from Azure.

In this blog post example (which mirrors a real world requirement I had), the situation is that whilst I need to write my SQL backups over a network share, I also want to push them up to Azure Storage (in a different region) to allow developers quicker downloads/restores. This is why I need to use AZCopy. If I only needed my backups to be written to Azure, I could have used BACKUP TO URL instead.

Read on to see how John did it.

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Changes to Azure SQL Database SLA

Published 2019-07-19 by Kevin Feasel

Arun Sirpal notes a change to the Azure SQL Database Service Level Agreement:

I am sure many missed the updates to Azure SQL Database SLA (Service Level Agreement). It used to be 99.99% across all tiers  but split between two different high-availability architectural models. Basic, Standard and General Purpose tiers had its own model and the Premium / Business Critical tiers had a different one.

Read on to see the change.

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Disk Utilization Per Drive in SQL Server

Published 2019-07-19 by Kevin Feasel

Max Vernon has a script which shows more than what xp_fixeddrives has to offer:

However, the command output doesn’t include the total size of each drive, making it impossible to determine the percent free space. If you’re in an environment where a separate team monitors disk space, and has alerts set when free space falls below a certain percentage, you may want to ensure you don’t breach those levels. The following script provides “the big picture” for your servers, since it provides total size, free space, available space, and the percent free. It does require the use of the documented and supported sys.xp_cmdshell system extended stored procedure. The code uses the drive letters returned by sys.xp_fixeddrives inside a cursor. Inside the cursor, we call the dos command fsutil volume diskfree C: to get total capacity and free space, etc:

Click through for the script.

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