.tip

Jun 23, 2026 · one of the small things

Read the code first, then the tests, as claims

Reading a test first primes you to accept the code it describes. Read the code, decide what you think it does, then open the tests and check whether they agree with you, not with the code. When the same agent wrote both, a green suite is the bare minimum and proves very little.

code-reviewtesting

Longer version: the post this came from.

~/tips/today — 2026-10-19

~cat tips/today

Never build an index on a live table without CONCURRENTLY

postgresqlmigrations

A plain CREATE INDEX takes a lock that blocks every write to the table for the whole build. On a big table that means minutes of outage that look like a hung app.

CREATE INDEX CONCURRENTLY orders_customer_idx ON orders (customer_id);

It's slower and can't run inside a transaction, so you'll have to tell your migration tool. If it fails halfway, it leaves an invalid index behind, so check pg_index.indisvalid and drop it before you retry.

↵ open y yesterday l ls /tips

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