Heads up: counting may be slow in PostgreSQL

The linked article points out that COUNT queries might be unexpectetly slow in psql.

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?

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Michael Leimstädtner

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Almost 3 years ago

Julian

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Source code in this card is licensed under the MIT License.

Upgrading Cucumber and Capybara to the latest versions available for Rails 2

Specify these gem versions in your Gemfile:

gem 'cucumber', '~> 1.3.0'
gem 'cucumber-rails', '= 0.3.2' # max version for Rails 2
gem 'capybara', '< 2' # capybara 2+ requires Rails 3
gem 'mime-types', '< 2' # dependeny of capybara

...

Posted by Michael Leimstädtner to makandra dev (2021-05-31 06:18)

Heads up: counting may be slow in PostgreSQL

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