Rebuild iterations automation index

For some reason the index creation failed on gitlab.com so
we are rebuilding it but we skip recreating the index if index
exists and is valid.

Changelog: fixed

db/migrate/20210527065005_add_index_for_cadence_iterations_automation.rb

@@ -8,18 +8,10 @@ class AddIndexForCadenceIterationsAutomation < ActiveRecord::Migration[6.0]
   disable_ddl_transaction!
 
   def up
-    return if index_exists_by_name?(:iterations_cadences, INDEX_NAME)
-
-    execute(
-      <<-SQL
-        CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON iterations_cadences
-        USING BTREE(automatic, duration_in_weeks, (DATE ((COALESCE("iterations_cadences"."last_run_date", DATE('01-01-1970')) + "iterations_cadences"."duration_in_weeks" * INTERVAL '1 week')))) 
-        WHERE duration_in_weeks IS NOT NULL
-      SQL
-    )
+    # no-op
   end
 
   def down
-    remove_concurrent_index_by_name :iterations_cadences, INDEX_NAME
+    # no-op
   end
 end

db/migrate/20210611100359_rebuild_index_for_cadence_iterations_automation.rb

+# frozen_string_literal: true
+
+class RebuildIndexForCadenceIterationsAutomation < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  INDEX_NAME = 'cadence_create_iterations_automation'
+
+  disable_ddl_transaction!
+
+  def up
+    return if index_exists_and_is_valid?
+
+    remove_concurrent_index_by_name :iterations_cadences, INDEX_NAME
+
+    disable_statement_timeout do
+      execute(
+        <<-SQL
+          CREATE INDEX CONCURRENTLY #{INDEX_NAME} ON iterations_cadences
+          USING BTREE(automatic, duration_in_weeks, (DATE ((COALESCE("iterations_cadences"."last_run_date", DATE('01-01-1970')) + "iterations_cadences"."duration_in_weeks" * INTERVAL '1 week')))) 
+          WHERE duration_in_weeks IS NOT NULL
+      SQL
+      )
+    end
+  end
+
+  def down
+    remove_concurrent_index_by_name :iterations_cadences, INDEX_NAME
+  end
+
+  def index_exists_and_is_valid?
+    execute(
+      <<-SQL
+        SELECT identifier
+        FROM postgres_indexes
+        WHERE identifier LIKE '%#{INDEX_NAME}' AND valid_index=TRUE
+      SQL
+    ).any?
+  end
+end

db/schema_migrations/20210611100359

+9429a8adca0bc85167f64e76d8d72b45d09d4303a01bd9c4ca39560bb4d89799
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