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Free-threaded Python in production: what actually broke

Python 3.14 made the no-GIL build officially supported, and the single-thread penalty fell from 40 percent to single digits. I moved a CPU heavy ingestion service across. The 3x speedup on the hot path was real, and so were three bugs that only exist without the lock. Tests caught none of them.

pythonconcurrencyperformance+1 more

Mar 24, 20268 min11 min

~/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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