.tip

May 6, 2026 · one of the small things

xargs -P is the parallel loop you already have

Processing a thousand files one at a time on an eight core machine wastes seven of the cores. xargs -P runs the command in parallel, and -n sets the batch size.

find . -name '*.png' -print0 | xargs -0 -P 8 -n 10 optimise

Use -print0 and -0, so a file name with a space in it doesn't turn into two arguments.

shell

~/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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