Notes
Short notes. TIL entries, one-off debugging stories, and things I want to remember next time I hit them. If you’re looking for the thinky stuff, the posts section is probably what you want.
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TIL: sqlite3 .backup is way better than .dump
The online backup API produces a consistent copy without locking writers.
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TIL: pytest's xfail strict flag fails if the test unexpectedly passes
Marking a test @pytest.mark.xfail(strict=True) fails CI if the bug got fixed and nobody un-xfailed.
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TIL: Go race detector can cause tests to pass that would fail in production
The race detector slows things down enough to hide some timing-dependent failures.
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TIL: GitHub Actions concurrency.cancel-in-progress
One line of workflow YAML stops CI from wasting minutes on outdated commits.
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TIL: DuckDB's COPY reads from S3 URLs directly
Point DuckDB at an s3:// URL and it will read Parquet files without downloading them first.
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TIL: pg_try_advisory_lock for cheap, per-key mutual exclusion
Turns out Postgres has application-level locks you can use without a lock table.
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TIL: SQLite has RETURNING now
SQLite 3.35 added RETURNING, so you can get the inserted row back in one round-trip.
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TIL: Grafana has a 'custom all value' for variables
When $var=All, Grafana was sending literally the string 'All' to my query. There's a setting for that.
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TIL: histogram_quantile needs a rate, not a raw counter
Forgetting the rate() inside histogram_quantile gives you weird-looking percentiles. Here's why.
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TIL: span events are the right place for timestamped annotations
Logs-within-a-span are a first-class OpenTelemetry concept and I had been putting them in attributes.
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TIL: OpenTelemetry has a separate 'Baggage' concept
Span attributes vs baggage — they're different and I had been confusing them.
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TIL: pg_stat_user_tables.n_mod_since_analyze is a thing
Shows exactly how many rows have changed since the last ANALYZE. Great for 'do I need to analyze?'
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TIL: just has variadic positional arguments
The +args and *args syntax in just is the thing I've been wanting.
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TIL: fzf's --preview can run arbitrary shell commands
The --preview flag is way more flexible than I realized.
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TIL: direnv layout_python just works
No more activating venvs manually. layout python in .envrc handles it.