full_table_scan_matchers

Detect full table scans in your unit tests! As opposed to just doing basic regexes on the db/schema.rb like rails-best-practices does, this actually checks queries made against the database, to ensure and assert that there are indexes for it to use.

Requirements/Support

• Ruby 2.0+
• ActiveRecord 4+
• ActiveSupport 4+
• mysql2 adapter

Installation

Add to your Gemfile, in the test group:

group :test do
  gem 'full_table_scan_matchers'
end

Usage

# No full table scans at all please:
expect { user.posts }.not_to full_table_scan

# Or on just a specific thing:
expect {
  user.posts.joins(:comments).first.comments
}.not_to full_table_scan.on :posts

How's it work?

• It logs all SQL queries made inside the expect block
  • ..optionally filtering them to table(s) you care about
• Afterwards, it runs all those through EXPLAIN
• Instead of checking type for ALL, it checks the keys instead
  • Because in test mode, mysql may ignore the index and scan the whole table because it's so small
  • But your production database is much, much larger - we just want to make sure that indexes are available

Configuration

You can optionally configure a few things:

FullTableScanMatchers.configure do |config|
  # Tables to ignore - defaults to none
  # Default: none
  config.ignores = []

  # Database adapter to use - only one for now
  # Default (and only): mysql
  config.adapter = FullTableScanMatchers::DBAdapters::MySql

  # Includes a backtrace in the fail output if this is set to true
  # Default: false
  config.log_backtrace = false

  # Add a proc to strip things from the logged backtraces
  # Default: None
  config.backtrace_filter = Proc.new { |backtrace| backtrace }

  # Run EXPLAIN on each SELECT statement immediately after it is executed
  # Default: false
  config.eager = false

  # Ignore full table scan on materialized subquery tables
  # Default: false
  config.ignore_materialized = false
end

Postgres?

Currently, this just support mySql. However, I tried to keep the part that's most-tied to that database (parsing the EXPLAIN output) silo'd in an adapter - I'd happily merge any clean PRs that add Postgres (or others)!

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests.

Credits

• Primary author: @JustinAiken
• A lot of inspiration comes from the excellent db-query-matchers by @brigade

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/JustinAiken/full_table_scan_matchers.

License

The gem is available as open source under the terms of the MIT License.