Add an index on vulnerability_occurrence_pipelines

Create (occurrence_id, id DESC) index on
vulnerability_occurrence_pipelines to speed up a query commonly executed
on Vulnerability Report section

Changelog: performance

db/post_migrate/20211028085926_add_occurrence_id_id_desc_index_to_vulnerability_occurrence_pipelines.rb

+# frozen_string_literal: true
+
+class AddOccurrenceIdIdDescIndexToVulnerabilityOccurrencePipelines < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  INDEX_NAME = "index_vulnerability_occurrence_pipelines_occurrence_id_and_id"
+
+  def up
+    add_concurrent_index(
+      :vulnerability_occurrence_pipelines,
+      [:occurrence_id, :id],
+      order: { id: :desc },
+      name: INDEX_NAME
+    )
+  end
+
+  def down
+    remove_concurrent_index_by_name(
+      :vulnerability_occurrence_pipelines,
+      INDEX_NAME
+    )
+  end
+end

db/schema_migrations/20211028085926

+ed6939c1e89f78290c312bf005cb33bd1a5ee778e8d9be3ae2eb04cc25416b92
\ No newline at end of file

db/structure.sql

@@ -27057,6 +27057,8 @@ CREATE INDEX index_vulnerability_occurrence_identifiers_on_identifier_id ON vuln
 
 CREATE UNIQUE INDEX index_vulnerability_occurrence_identifiers_on_unique_keys ON vulnerability_occurrence_identifiers USING btree (occurrence_id, identifier_id);
 
+CREATE INDEX index_vulnerability_occurrence_pipelines_occurrence_id_and_id ON vulnerability_occurrence_pipelines USING btree (occurrence_id, id DESC);
+
 CREATE INDEX index_vulnerability_occurrence_pipelines_on_pipeline_id ON vulnerability_occurrence_pipelines USING btree (pipeline_id);
 
 CREATE INDEX index_vulnerability_occurrences_deduplication ON vulnerability_occurrences USING btree (project_id, report_type, project_fingerprint);