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ruth mhlanga
ruth mhlanga

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The Misguided Quest for Low-Latency Queries: A Cautionary Tale of Warehouse Cost Optimisation

The Problem We Were Actually Solving

Our warehouse was serving millions of game events each day, resulting in 300-second query latency. Our non-technical stakeholders, including the game developers and analysts, couldn't fathom how such a simple query could take this long. They pleaded for faster results, and we took it as a personal challenge to get those numbers down. The pressure was on, and the stakes were high. We decided to go all-in on a fully managed warehouse service, eager to cut latency by leveraging serverless architectures and automated scalability.

What We Tried First (And Why It Failed)

We embarked on a serverless warehouse odyssey, switching from our self-managed Postgres database to a fully managed one offered by a prominent cloud provider. We optimistically assumed it would magically reduce latency by 90% and eliminate the need for manual scaling. Our initial configuration leaned heavily on the defaults, hoping to 'set it and forget it.' However, in hindsight, this hasty approach failed to account for our complex data ingestion patterns and specific query semantics. Within five days, our query latency shot back up to a whopping 6 minutes, far exceeding our initial self-managed numbers. We found ourselves scrambling to debug the configuration, but the complexity of our data pipeline made it a daunting task.

The Architecture Decision

After months of trial and error, we made the bold decision to transition to a hybrid warehouse model. Instead of relying solely on serverless, we decided to reserve our fully managed warehouse for simple queries and analytics. We also implemented a custom Postgres instance for complex, low-latency operations. By creating a clear tiering strategy, we could dedicate our resources efficiently and reduce the load on our managed warehouse. Furthermore, we adopted a configuration-first approach, where our data engineer would carefully tune and validate our warehouse settings before deploying any new code. This deliberate, iterative process gradually improved our query latency, landing us at a respectable 5 seconds.

What The Numbers Said After

As we worked tirelessly to optimise our warehouse configuration, we encountered numerous plateaus and local optima. However, our decision to use a hybrid warehouse model paid off in the end. Our query latency dropped by 85%, our query cost plummeted by 75%, and we were able to meet our freshness SLA of 10 minutes by introducing a sophisticated data quality framework at the ingestion boundary. We now process 2 million game events per second, a number that continues to grow. Our data quality framework ensures that 99.95% of our data meets our integrity requirements, making it easier to rely on our warehouse for game insights and analysis.

What I Would Do Differently

If I'm being honest, I would've invested more time in understanding our data ingestion patterns and query semantics from the get-go. In hindsight, I would've resisted the temptation to rely on defaults, opting for a more nuanced configuration approach that accounted for our data ecosystem's unique characteristics. Additionally, I would have considered a more gradual rollout of our hybrid warehouse model, rather than trying to switch everything overnight. The iterative process we underwent ultimately led to a more resilient and optimised warehouse, but it would've been nice to arrive there sooner, with fewer missteps along the way.

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