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Diffstat (limited to 'doc/development/query_recorder.md')
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1 files changed, 18 insertions, 1 deletions
diff --git a/doc/development/query_recorder.md b/doc/development/query_recorder.md index 17f2fecc1bc..371d6e0e49e 100644 --- a/doc/development/query_recorder.md +++ b/doc/development/query_recorder.md @@ -1,5 +1,5 @@ --- -stage: Enablement +stage: Data Stores group: Database info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments --- @@ -24,10 +24,27 @@ it "avoids N+1 database queries" do end ``` +You can if you wish, have both the expectation and the control as +`QueryRecorder` instances: + +```ruby +it "avoids N+1 database queries" do + control = ActiveRecord::QueryRecorder.new { visit_some_page } + create_list(:issue, 5) + action = ActiveRecord::QueryRecorder.new { visit_some_page } + + expect(action).not_to exceed_query_limit(control) +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. 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. +If this test fails, and the control was passed as a `QueryRecorder`, then the +failure message indicates where the extra queries are by matching queries on +the longest common prefix, grouping similar queries together. + ## Cached queries By default, QueryRecorder ignores [cached queries](merge_request_performance_guidelines.md#cached-queries) in the count. However, it may be better to count |