Deep Dive
0.1 Plus 0.2 Is Not 0.3, and Your Checkout Noticed
Currency stored as a float accumulates fractions of a cent that are invisible per transaction and visible in the reconciliation.
DevOps
Six Months of Running MicroVMs in Production
What broke, what surprised me, and what I would tell someone considering Firecracker for their own platform.
Deep Dive
Vacuum, Dead Tuples and the Wraparound Shutdown Nobody Plans For
MVCC gives every transaction an id and keeps old row versions until vacuum says they are dead to everyone. If vacuum falls behind for long enough, the id…
Deep Dive
TLS Session Resumption, and the Handshake That Never Got Faster
Resumption was enabled everywhere and the repeat handshakes were still full handshakes. Session tickets need a shared key across every backend, and behind a…
Deep Dive
Your Container Has Two CPUs and Is Using One Point Three
The container's CPU limit is two cores and its usage never exceeds one point three, yet requests slow down. CFS quota throttles in hundred millisecond…
Deep Dive
Node Event Loop Phases: Where Your setTimeout Really Runs
setTimeout zero and setImmediate are not the same thing, and which one runs first depends on where in the event loop you called them.
Deep Dive
HTTP/2 Fixed Head of Line Blocking, Then Reintroduced It
HTTP/2 multiplexed many streams over one connection to escape head of line blocking, then moved the blocking one layer down into TCP, where a single lost…
Deep Dive
Every Layer That Caches a DNS Answer Between You and the Record
A DNS answer passes through four or five caches before it reaches your code, each with its own TTL and its own opinion.
Deep Dive
How the Linux OOM Killer Chooses, and Why It Picked Your App
Under memory pressure the kernel kills one process and not another, and it is not random. The oom score is a small arithmetic formula you can read, tune and…
Deep Dive
TCP Keep Alive and HTTP Keep Alive Are Not the Same Feature
They share a name and almost nothing else. One is a kernel probe that fires after two hours of silence. The other is connection reuse you can watch in the…
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.