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To simulate the effects of deployments on a workload, I built a small client. It’s nothing great, and likely some of you will laugh at my C# skills, but it works well enough. It’s a simple Windows form application that writes to a text box. However, it’s valuable to determine if there are any issues when you’ve made a deployment.
This post looks at the rough design of the client. Code is available in this repo: https://github.com/way0utwest/ZeroDowntime
Using WPF
I wrote a small app a few years ago to test and present on Always Encrypted. This was a basic WPF app that added the proper values to the connection string for Always Encrypted and let you query encrypted data (or not).
Like all mediocre developers, I copied and pasted that project into a new folder and set about modifying it. In this case, I set up a loop that continues to run and execute some database code, essentially using this loop:
while (iRunQuery > 0)
{
I set this value to 0 initially, and when a button is clicked, it’s 1. This then runs a bunch of lines to decide which DB code to run. I’ve mostly made this stored procedures to make it easier to adjust demos without touching C# code.
It’s not pretty.
At the bottom, I have this (outside the loop)
Application.DoEvents();
System.Threading.Thread.Sleep(100);
This is designed to catch me clicking a “stop” button that will set the variable back to 0. I added the delay because otherwise this runs a bit fast.
I have a few option buttons that adjust what code I’m calling, so I can simulate toggling feature flags on and off. I also log results to a window so you can see them, and I catch errors and log those. Errors are also counted, so we can see the impact of “non zero-downtime” changes.
It’s not a great example of software, but it does work.
Voice of the DBA 