Performance regression in GET /api/:version/groups/:id/merge_requests

Summary

The GET /api/:version/groups/:id/merge_requests endpoint is experiencing a performance regression caused by !217325 (merged).

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Root Cause

Merge request !217325 (merged) introduced two new methods to MergeRequest:

  • committer_ids_to_filter_from_approvers
  • committers_to_filter_from_approvers

These methods are called during approval rule filtering when the approval_policy_rules_individual_approvers_filtering feature flag is enabled. The issue is:

  1. These methods call committers() with lazy: true, which triggers preload_commits_metadata()
  2. This preloading happens for every merge request in the API response
  3. The ActiveRecord preloader inefficiently loads association data, causing expensive reflection calls in activerecord/reflection.rb:930:in 'association_primary_key'
  4. This creates N+1 query patterns and excessive preloading overhead

Backtrace Evidence 

activerecord (7.2.3) lib/active_record/reflection.rb:930:in `association_primary_key'
activerecord (7.2.3) lib/active_record/associations/preloader/association.rb:162:in `association_key_name'
activerecord (7.2.3) lib/active_record/associations/preloader/association.rb:205:in `block in load_records'
...
app/models/merge_request.rb:907:in `preload_commits_metadata'
app/models/merge_request.rb:913:in `block in committers'
app/models/merge_request.rb:930:in `committers_to_filter_from_approvers'
ee/app/models/approval_wrapped_rule.rb:251:in `filter_committers_for_rule'

Impact

  • Slow API response times for endpoints listing merge requests
  • Excessive database queries and reflection calls
  • Performance degradation scales with the number of merge requests and approval rules

Related Issues

  • Related to !217325 (merged) - Filter approval rule approvers individually
  • Related to #574854 - Original issue that MR217325 was addressing
Edited by 🤖 GitLab Bot 🤖