1.9 KiB
QueryRecorder
QueryRecorder is a tool for detecting the N+1 queries problem from tests.
Implemented in spec/support/query_recorder.rb via 9c623e3e
As a rule, merge requests should not increase query counts. If you find yourself adding something like .includes(:author, :assignee) to avoid having N+1 queries, consider using QueryRecorder to enforce this with a test. Without this, a new feature which causes an additional model to be accessed will silently reintroduce the problem.
How it works
This style of test works by counting the number of SQL queries executed by ActiveRecord. First a control count is taken, then you add new records to the database and rerun the count. If the number of queries has significantly increased then an N+1 queries problem exists.
it "avoids N+1 database queries" do
control_count = ActiveRecord::QueryRecorder.new { visit_some_page }.count
create_list(:issue, 5)
expect { visit_some_page }.not_to exceed_query_limit(control_count)
end
As an example you might create 5 issues in between counts, which would cause the query count to increase by 5 if an N+1 problem exists.
Note: In some cases the query count might change slightly between runs for unrelated reasons. In this case you might need to test
exceed_query_limit(control_count + acceptable_change), but this should be avoided if possible.
See also
- Bullet For finding
N+1query problems - Performance guidelines
- Merge request performance guidelines