Heads up: Counting may be slow in PostgreSQL

The linked article points out that COUNT queries might be unexpectedly slow in PostgreSQL.

If you just need to know "are there any records" use any?. This uses SELECT 1 AS one FROM ... LIMIT 1 under the hood.
If you just need to know "are there no records" use empty? or none?. This uses SELECT 1 AS one FROM ... LIMIT 1 under the hood.

In short: Replace foo.count > 0 with foo.any? or foo.count == 0 with foo.none?

If you require quick counts and can tolerate some level of imprecision, consider exploring the fast_count Show archive.org snapshot gem.

Related

You may circumvent this by using SQL: Fast threshold counts with LIMIT