.tip

May 13, 2026 · one of the small things

Webhooks arrive twice, so store the event id

Providers retry when your endpoint is slow, and a retry is the same event all over again. The usual result is charging a customer twice.

INSERT INTO webhook_events (id) VALUES ($1) ON CONFLICT DO NOTHING RETURNING id;
-- no row returned: already processed, respond 200 and stop

Insert the event id first, in the same transaction as the work. Answer 200 quickly and do the slow part from a queue.

securitydistributed-systems

~/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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