https://schew2381.github.io/A minimal, responsive and feature-rich Jekyll theme for technical writing. 2026-07-15T04:10:43-07:00 Seiji Chew https://schew2381.github.io/ Jekyll © 2026 Seiji Chew /assets/img/favicons/favicon.ico /assets/img/favicons/favicon-96x96.png 2026-03-04T18:00:00-08:00 2026-04-08T17:23:03-07:00 https://schew2381.github.io/posts/how-postgres-concurrent-index-creation-works/ Seiji Chew

CREATE INDEX takes a SHARE lock on the table for the entire build. That blocks all writes, which could be minutes or hours of downtime for large tables. CREATE INDEX CONCURRENTLY avoids this by splitting the work across multiple transactions with weaker locks. The internal mechanism is non-trivial. This post traces through the source code to explain exactly what happens. The core problem A n...