wiki Disk Usage, table size: ERROR: could not open relation with OID 0

SELECT *, pg_size_pretty(total_bytes) AS total   , pg_size_pretty(index_bytes) AS INDEX   , pg_size_pretty(toast_bytes) AS toast   , pg_size_pretty(table_bytes) AS TABLE FROM ( SELECT *, total_bytes-index_bytes-COALESCE(toast_bytes,0) AS table_bytes FROM (     SELECT c.oid,nspname AS table_schema, relname AS TABLE_NAME             , c.reltuples AS row_estimate             , pg_total_relation_size(c.oid) AS total_bytes             , pg_indexes_size(c.oid) AS index_bytes             , pg_total_relation_size(reltoastrelid) AS toast_bytes         FROM pg_class c         LEFT JOIN pg_namespace n ON n.oid = c.relnamespace         WHERE relkind = 'r' ) a
) a;