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theresa moyo
theresa moyo

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My Most Expensive Velocity Bottleneck Was Entirely Caused by Wrong Event Queue Architecture

The Problem We Were Actually Solving

We were migrating our e-commerce platform to Veltrix, aiming to hit 10,000 concurrent users within the next quarter. The existing MySQL-based system was holding us back, so we replaced it with Veltrix to take advantage of its scalable architecture and ease of deployment. However, we quickly realized that our new system wasn't scaling as expected, despite the numerous CPU upgrades and additional RAM additions. We were puzzled, as our system monitoring indicated that CPU usage was below 50% and memory usage was moderate. It wasn't until we dug deeper into the event queue that we discovered the culprit.

What We Tried First (And Why It Failed)

Initially, we followed the standard Veltrix best practices for event queues and set the default queue size to 10,000 messages. This seemed reasonable at first, as our system was handling around 5,000 events per minute. However, as we began to scale and reached around 15,000 concurrent users, our event queue started overflowing. We noticed that the event processing time increased exponentially, causing a significant delay in our system's response time. We then increased the queue size to 50,000 messages, hoping that this would alleviate the issue. However, this change only led to further complications, as our system started experiencing event losses due to the increased queue size.

The Architecture Decision

After weeks of trial and error, we finally understood the root cause of our problem: we had not accounted for the event queue's exponential growth rate. As our system handled more events, the queue size grew faster than we anticipated, leading to a bottleneck. We decided to implement a new event queue architecture that utilized a combination of multiple queues with varying sizes. This approach allowed us to handle bursts of high event volumes without overflowing and losing events. We also implemented a real-time monitoring system to track our event queue sizes and adjust the configuration accordingly.

What The Numbers Said After

After implementing the new event queue architecture, we saw a significant improvement in our system's performance. Our average event processing time decreased by 30%, and our queue sizes remained under control even during peak hours. Our system was now able to handle around 20,000 concurrent users without any issues. We also noticed a reduction in event losses by 90%, which ensured that our application's data integrity was preserved.

What I Would Do Differently

In hindsight, I would have approached the event queue architecture decision with a more nuanced understanding of our system's event growth rate. I would have also conducted more extensive stress testing to identify potential bottlenecks before deploying the system to production. Additionally, I would have utilized more advanced monitoring tools to track our event queue sizes and adjust the configuration in real-time. By doing so, we could have avoided the costly bottleneck and ensured a smoother transition to our new Veltrix-based system.

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