.tip

Jun 2, 2026 · one of the small things

An Idempotency-Key header makes a retried POST safe

A client that times out can't tell whether the order was created. With the header, it retries the same request with the same key and gets the same response back, not a second order.

POST /orders
Idempotency-Key: 4a7c…

Store the key with the response for 24 hours. A repeat with the same key gets the stored response, and the same key with a different body gets a 422.

httpapi-design

~/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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