Where database blog posts get flame-broiled to perfection
Ah, another blog post fresh from the "what could possibly go wrong?" department. I read "dug deeper into all the ideas" and my pager started vibrating preemptively. As the guy who gets to shepherd these theoretical performance gains into the harsh, unforgiving light of production, allow me to offer my annotations.
So, we've "fixed" the optimizer. Again. This is fantastic news for anyone who loves high-stakes gambling. I'm sure this complex, system-wide change, which promises to automagically make everything faster, will have absolutely no unforeseen impact on that one mission-critical, horribly written query from 2014 that keeps the entire billing system afloat. I look forward to discovering its new, genius query plan—the one that eschews a perfectly good index in favor of a full table scan and a cross-join with the user-sessions table. It's not a bug, it's emergent behavior.
My favorite part is always the upgrade path. The developers will assure me it’s a "zero-downtime" change. “Just a simple flag you can enable on the fly!” they’ll chirp, blissfully unaware of what that means across a 40-node cluster with active replication. In reality, this means a 2 AM change window, a meticulously planned series of rolling restarts, and me sacrificing a rubber chicken to the connectivity gods, all while praying the new logic doesn't introduce a subtle data drift that we won't notice for three weeks.
Naturally, the monitoring for this groundbreaking feature will be... non-existent. How will we know if the new optimizer is actually optimizing? Oh, we won't. There won’t be a new metric in Prometheus, no new dashboard in Grafana. The success metric will be a lack of all-caps messages in the emergency Slack channel. I'll just be staring at the CPU_UTILIZATION graph, trying to divine the database's mood like a modern-day haruspex reading goat entrails.
The blog post mentioned "analysis." My analysis is that my mean-time-to-sleep is about to take a nosedive.
I can already see it. It’s 3:17 AM on the Saturday of Memorial Day weekend. The e-commerce site has ground to a halt. Why? Because the annual "Inactive Users With a Prime Number of Past Orders" cleanup job just kicked off, and the new optimizer has decided this is the perfect time to materialize a 500GB temporary table. PagerDuty will scream the anthem of my people, and I'll be debugging an execution plan on my phone while my grill runs out of propane. "Enhanced for MySQL" is about to be enhanced with my tears.
You know, I have a drawer full of vendor stickers for databases that promised to solve everything. TokuDB, RethinkDB, FoundationDB before Apple bought them… they all had great blog posts, too. They’re peeling now, stuck to the lid of a laptop I keep just for serial console access. This new "improvement" feels less like an engineering milestone and more like a fresh piece of vinyl for my collection of broken promises.
Anyway, time to go pre-write the incident post-mortem. It saves time later.