.tip

Nov 8, 2025 · one of the small things

Set lock_timeout before any ALTER TABLE

ALTER TABLE waits for a lock, and while it waits, every query behind it queues up too. One long-running report can turn a one millisecond migration into a full outage.

SET lock_timeout = '3s';
ALTER TABLE orders ADD COLUMN note text;

If the lock doesn't come within three seconds, the migration fails and you retry once the report is done. Failing fast is exactly what you want here.

postgresqlmigrations

~/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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