Bug Hunt
Logged In Users Saw Somebody Else's Search Results
A support ticket said search was returning the wrong products. It was returning the right products for somebody else.
Docker
Why Your Docker Build Reinstalls Every Dependency Every Time
One changed byte early in a Dockerfile throws away everything after it. Here is how the cache key is computed and how to order instructions so it survives.
PostgreSQL
Autovacuum Is Running and Your Table Is Still Bloating
Dead tuples that never get reclaimed, a table twice the size of its data, and queries getting slower every week. Here is what blocks vacuum and how to see it.
DevOps
Consumer Lag Is Not a Throughput Problem Until You Prove It Is
Lag climbing on one partition while the rest keep up tells you something specific. Here is how to read the numbers before you add consumers that cannot help.
JavaScript
The Dashboard That Got Slower the Longer You Left It Open
A single page app that was fine for an hour and unusable by the afternoon. Three wrong hypotheses, then a heap snapshot showed forty thousand detached DOM…
MicroVMs
Your Database Got Slower and Nothing in Your Code Changed
Query times doubling at unpredictable hours with no deploy and no traffic spike. When the cause is not in your process, it is usually not on your machine…
Shopify
How Many Shopify Apps Is Too Many? I Measured It
Everyone says apps slow your store down. Almost nobody says by how much. Here are measurements from real stores and a method for auditing your own.
Python
Debugging asyncio Deadlocks and the Blocking Call Checklist
Your async service handles ten requests a second and pegs one core. Somewhere a synchronous call is blocking the event loop.
Shopify
The Liquid Loop That Adds Three Seconds to Your Shopify Page
Liquid has no query log, so N+1 problems are invisible until the page is slow. Here is how to find them with Server-Timing and how to restructure the loops.
Databases
Your Cache Serves Stale Data and the Bug Is Invalidation
Reading from cache is easy. Knowing when to remove something is where the bugs live, and most of them are races.
Shopify
Shopify Theme Scores 40 on Lighthouse: The Fix Order
Most Shopify performance advice is a list of tips in no particular order. Here is how to measure first, find the actual cause, and fix things in the order…
JavaScript
Debugging Slow TypeScript Builds With generateTrace
Your editor takes four seconds to show a type error and tsc takes two minutes. There is a profiler for this and almost nobody uses it.