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Notes on backend architecture, performance work, and the WordPress and Laravel systems I build.

Aug 16, 202616 min read
SELECT COUNT(*) is slow on 30M rows: how to make counting fast at scale
Why COUNT(*) degrades on a 30M-row table under MVCC, and the full ladder of fixes — keyset pagination, planner estimates, capped counts, covering indexes, sharded summary counters, rollup tables and OLAP replicas — with the MySQL and PostgreSQL code for each and a table for picking the right one.
Intermediate
- Databases
- Performance
- MySQL
- PostgreSQL