Merge branch 'yorick/environments-filtering-performance' into 'master'

Improve performance of filtering merge requests by an environment

See merge request gitlab-org/gitlab!45796

app/models/deployment_merge_request.rb

@@ -14,7 +14,12 @@ class DeploymentMergeRequest < ApplicationRecord
   end
 
   def self.deployed_to(name)
+    # We filter by project ID again so the query uses the index on
+    # (project_id, name), instead of using the index on
+    # (name varchar_pattern_ops). This results in better performance on
+    # GitLab.com.
     where('environments.name = ?', name)
+      .where('environments.project_id = merge_requests.target_project_id')
   end
 
   def self.deployed_after(time)