cbc20d2b7f
This was being masked by the statement cache because only one author was used per issue in the test.. Also adds support for an Rspec matcher `exceed_all_query_limit`.
7.3 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.
Cached queries
By default, QueryRecorder will ignore cached queries in the count. However, it may be better to count
all queries to avoid introducing an N+1 query that may be masked by the statement cache. To do this,
pass the skip_cached variable to QueryRecorder and use the exceed_all_query_limit matcher:
it "avoids N+1 database queries" do control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) { visit_some_page }.count create_list(:issue, 5) expect { visit_some_page }.not_to exceed_all_query_limit(control_count) end
## Finding the source of the query
It may be useful to identify the source of the queries by looking at the call backtrace.
To enable this, run the specs with the `QUERY_RECORDER_DEBUG` environment variable set. For example:
QUERY_RECORDER_DEBUG=1 bundle exec rspec spec/requests/api/projects_spec.rb
This will log calls to QueryRecorder into the `test.log`. For example:
QueryRecorder SQL: SELECT COUNT(*) FROM "issues" WHERE "issues"."deleted_at" IS NULL AND "issues"."project_id" = $1 AND ("issues"."state" IN ('opened')) AND "issues"."confidential" = $2
--> /home/user/gitlab/gdk/gitlab/spec/support/query_recorder.rb:19:in callback' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/fanout.rb:127:in finish'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/fanout.rb:46:in block in finish' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/fanout.rb:46:in each'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/fanout.rb:46:in finish' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/instrumenter.rb:36:in finish'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications/instrumenter.rb:25:in instrument' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract_adapter.rb:478:in log'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:601:in exec_cache' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:585:in execute_and_clear'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/postgresql/database_statements.rb:160:in exec_query' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:356:in select'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:32:in select_all' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract/query_cache.rb:68:in block in select_all'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract/query_cache.rb:83:in cache_sql' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/connection_adapters/abstract/query_cache.rb:68:in select_all'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/relation/calculations.rb:270:in execute_simple_calculation' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/relation/calculations.rb:227:in perform_calculation'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/relation/calculations.rb:133:in calculate' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activerecord-4.2.8/lib/active_record/relation/calculations.rb:48:in count'
--> /home/user/gitlab/gdk/gitlab/app/services/base_count_service.rb:20:in uncached_count' --> /home/user/gitlab/gdk/gitlab/app/services/base_count_service.rb:12:in block in count'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:299:in block in fetch' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:585:in block in save_block_result_to_cache'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:547:in block in instrument' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/notifications.rb:166:in instrument'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:547:in instrument' --> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:584:in save_block_result_to_cache'
--> /home/user/.rbenv/versions/2.3.5/lib/ruby/gems/2.3.0/gems/activesupport-4.2.8/lib/active_support/cache.rb:299:in fetch' --> /home/user/gitlab/gdk/gitlab/app/services/base_count_service.rb:12:in count'
--> /home/user/gitlab/gdk/gitlab/app/models/project.rb:1296:in `open_issues_count'
## See also
- [Bullet](profiling.md#Bullet) For finding `N+1` query problems
- [Performance guidelines](performance.md)
- [Merge request performance guidelines](merge_request_performance_guidelines.md#query-counts)