psql -q
maxim=> create  temp table a (id integer primary key, val int not null);
maxim=> create index a_val on a(val);
maxim=> insert into a values (1, 1);
maxim=> \dt+ a
                      List of relations
  Schema   | Name | Type  | Owner |    Size    | Description 
-----------+------+-------+-------+------------+-------------
 pg_temp_3 | a    | table | maxim | 8192 bytes | 
(1 row)

maxim=> select pg_size_pretty(pg_total_relation_size('a'));
 pg_size_pretty 
----------------
 40 kB
(1 row)

maxim=> explain analyze select * from a;
                                          QUERY PLAN                                           
-----------------------------------------------------------------------------------------------
 Seq Scan on a  (cost=0.00..32.60 rows=2260 width=8) (actual time=0.016..0.017 rows=1 loops=1)
 Planning Time: 0.188 ms
 Execution Time: 0.051 ms
(3 rows)

maxim=> select 'update a set val=val+1 where id=1;' from generate_series(1, 1000000)
maxim-> \gexec
maxim=> select pg_size_pretty(pg_total_relation_size('a'));
 pg_size_pretty 
----------------
 48 MB
(1 row)

maxim=> explain analyze select * from a;
                                              QUERY PLAN                                              
------------------------------------------------------------------------------------------------------
 Seq Scan on a  (cost=0.00..11204.62 rows=776762 width=8) (actual time=21.329..21.330 rows=1 loops=1)
 Planning Time: 0.102 ms
 Execution Time: 21.353 ms
(3 rows)