One NULL can empty a SQL exclusion query
A NOT IN query can lose every candidate when its exclusion set contains NULL. A small SQLite example shows why and how a correlated NOT EXISTS changes the result.
Wildness 1/5 · Tamed
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Two Python datetimes can compare equal an hour apart
During a repeated local hour, two timezone-aware Python datetimes can compare equal. Convert to UTC before comparing instants or calculating elapsed time.
Wildness 1/5 · TamedPython zip can hide a missing result
When Python pairs separately produced values, a missing result can vanish silently. Strict pairing catches unequal lengths, with an important limit around side effects.
Wildness 1/5 · TamedWhat a Chance of Rain Is Actually Saying
A chance of rain is a probability about a specific point reaching 0.01 inch during a period. It is not a duration and not an area, as the National Weather Service defines it.
Wildness 1/5 · TamedThe Table Cell That Looks Empty
An empty cell is not simply nothing. Under default tabular-data metadata it is a null value, and the reason it is empty does not survive unless you give it a column of its own.
Wildness 1/5 · TamedA Number With a Unit Is Still a Claim
Why a measurement is a number and a unit together, and how dropping a required unit turns a claim into noise, worked through a hypothetical constant-power energy calculation.
Wildness 1/5 · TamedModel a tagged stream of model events with serde internally tagged enums
Map a JSON event stream with a "type" field onto a Rust enum using #[serde(tag = "type")], handle unknown event types, and see why tuple variants fail to compile.
Wildness 1/5 · TamedKeep a changelog that humans read, grouped by type of change
Keep a CHANGELOG.md with an Unreleased section and Added, Changed, Deprecated, Removed, Fixed and Security groups, so users can see what changed and what will break.
Wildness 1/5 · TamedCatch undefined behavior in unsafe Rust with Miri
Run cargo miri test on a crate with unsafe code to catch out-of-bounds reads, use-after-free and aliasing violations that pass ordinary tests.
Wildness 1/5 · TamedArchitecture decision records: write down why, not only what
An architecture decision record is a short file in your repository that explains one design choice: its context, the decision, its status and its consequences.
Wildness 1/5 · TamedRun each Rust test in its own process with cargo-nextest
Switch a Rust test suite to cargo-nextest so each test runs in its own process, flaky tests can retry, and slow or hung tests are flagged and stopped.
Wildness 1/5 · TamedAssign an incident commander, a scribe and a communications lead
Split incident duties into named roles with explicit handover rules, so the people fixing the problem are not also writing updates and keeping the timeline.
Wildness 1/5 · TamedError types for a Rust library, and a different answer for a binary
A library's error type is public API that callers match on. A binary mostly needs a clear message with context. thiserror and anyhow fit those two jobs.
Wildness 1/5 · TamedLink every alert to its runbook with a Prometheus annotation
Add summary and runbook_url annotations to Prometheus alerting rules, render them in Alertmanager templates, and test them so the on-call link never goes missing.
Wildness 1/5 · TamedMirror production traffic to a new model version before it serves users
Use an Istio VirtualService to copy live requests to a candidate model deployment, discard its responses, and compare its errors and latency with the stable version.
Wildness 1/5 · TamedLiveness and readiness probes answer different questions
Liveness decides whether Kubernetes restarts a container. Readiness decides whether it gets traffic. Wiring one health check to both turns a slow dependency into a restart storm.
Wildness 1/5 · TamedCopying a live SQLite file is a gamble, and the backup command exists for it
A plain file copy of a SQLite database that a program is still using can be inconsistent or miss recent writes. What SQLite's own documentation says goes wrong, and three supported ways to take a safe copy.
Wildness 2/5 · Mostly tamedAdding a column in SQLite does not rewrite the table
ALTER TABLE ADD COLUMN in SQLite edits the stored schema text and leaves the rows alone, so it takes the same time on one row or ten million. The same design explains the limits on what kind of column you can add.
Wildness 2/5 · Mostly tamedCargo starts one compiler per CPU, and memory may run out first
Cargo's default job count is the number of logical CPUs. On a machine with many cores and several builds at once, memory becomes the limit long before CPU. Three ways to set the job count, and how to pick one.
Wildness 2/5 · Mostly tamedA CPU percentage needs two readings
Linux records how much CPU time a process has used, never a percentage. Every percent figure is a difference over an interval, which is why ps and top disagree and why a tool can print a confident zero.
Wildness 2/5 · Mostly tamedOne systemd setting keeps a service out of swap
MemorySwapMax=0 on a systemd unit stops that one service from being swapped out while the rest of the machine still can be. How to set it, read it back and undo it, and what it costs.
Wildness 2/5 · Mostly tamedA swapped-out process looks small in a memory list
A process list sorted by resident memory can hide the largest holder, because memory pushed to swap no longer counts as resident. Where Linux records the swapped part, and a one-line way to rank by both.
Wildness 2/5 · Mostly tamedWhy your servers disagree about the time
Two machines' logs that don't line up can mean one clock isn't synchronised, or that time zones got mixed. How to check sync on Linux, and which clock to use for timestamps and for durations.
Wildness 1/5 · TamedWhat a model ID actually pins
Some model names are fixed snapshots and some are pointers that move. How Anthropic and OpenAI name their models, how to tell which kind you are calling, and what even a pinned ID does not freeze.
Wildness 1/5 · Tamed
