Remove extra index

Remove extra index from structure.sql

changelogs/unreleased/325605-query-performance-investigation-4458344713234267000-select-merge_r.yml

+---
+title: Add additional index to merge_requests table for project/status/created_at
+merge_request: 57267
+author:
+type: performance

db/migrate/20210323182846_add_project_status_date_index_to_merge_requests.rb

+# frozen_string_literal: true
+
+class AddProjectStatusDateIndexToMergeRequests < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = "idx_mrs_on_target_id_and_created_at_and_state_id"
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :merge_requests, %i[target_project_id state_id created_at id], name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :merge_requests, INDEX_NAME
+  end
+end

db/schema_migrations/20210323182846

+9ee014f462ec0d2affaab146243fb991298e9b30bd57b741fba0440b1676de03
\ No newline at end of file

db/structure.sql

@@ -21706,6 +21706,8 @@ CREATE UNIQUE INDEX idx_metrics_users_starred_dashboard_on_user_project_dashboar
 
 CREATE INDEX idx_mr_cc_diff_files_on_mr_cc_id_and_sha ON merge_request_context_commit_diff_files USING btree (merge_request_context_commit_id, sha);
 
+CREATE INDEX idx_mrs_on_target_id_and_created_at_and_state_id ON merge_requests USING btree (target_project_id, state_id, created_at, id);
+
 CREATE UNIQUE INDEX idx_on_compliance_management_frameworks_namespace_id_name ON compliance_management_frameworks USING btree (namespace_id, name);
 
 CREATE UNIQUE INDEX idx_on_external_approval_rules_project_id_external_url ON external_approval_rules USING btree (project_id, external_url);