Replacement partial index for ci_builds.token

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/333812

Changelog: performance

db/post_migrate/20210616145254_add_partial_index_for_ci_builds_token.rb

+# frozen_string_literal: true
+
+class AddPartialIndexForCiBuildsToken < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  NAME = 'index_ci_builds_on_token_partial'
+
+  def up
+    add_concurrent_index :ci_builds, :token, unique: true, where: 'token IS NOT NULL', name: NAME
+  end
+
+  def down
+    remove_concurrent_index_by_name :ci_builds, NAME
+  end
+end

db/schema_migrations/20210616145254

+525fbdd66dcabbf1e6d0430468600f86fbc3c00dcfdab1c5a052294d7d73de37
\ No newline at end of file

db/structure.sql

@@ -22830,6 +22830,8 @@ CREATE UNIQUE INDEX index_ci_builds_on_token ON ci_builds USING btree (token);
 
 CREATE UNIQUE INDEX index_ci_builds_on_token_encrypted ON ci_builds USING btree (token_encrypted) WHERE (token_encrypted IS NOT NULL);
 
+CREATE UNIQUE INDEX index_ci_builds_on_token_partial ON ci_builds USING btree (token) WHERE (token IS NOT NULL);
+
 CREATE INDEX index_ci_builds_on_updated_at ON ci_builds USING btree (updated_at);
 
 CREATE INDEX index_ci_builds_on_upstream_pipeline_id ON ci_builds USING btree (upstream_pipeline_id) WHERE (upstream_pipeline_id IS NOT NULL);