Вы правы
select pg_table_size('t1'),pg_relation_size('t1'),(select oid||':'||relfilenode from pg_class where relname='t1');
pg_table_size | pg_relation_size | ?column?
---------------+------------------+-------------
761856 | 753664 | 16438:16455
(1 row)
postgres=# select pg_table_size('t1'),pg_relation_size('t1'),(select oid||':'||relfilenode from pg_class where relname='t1');
pg_table_size | pg_relation_size | ?column?
---------------+------------------+-------------
57344 | 57344 | 16438:16842
(1 row)
postgres=# rollback ;
ROLLBACK
postgres=# select pg_table_size('t1'),pg_relation_size('t1'),(select oid||':'||relfilenode from pg_class where relname='t1');
pg_table_size | pg_relation_size | ?column?
---------------+------------------+-------------
761856 | 753664 | 16438:16455
(1 row)
postgres=# begin;
BEGIN
postgres=# alter table t1 alter COLUMN sss type bigint using substring(sss from 1 for 2)::bigint;ALTER TABLE
postgres=# select pg_table_size('t1'),pg_relation_size('t1'),(select oid||':'||relfilenode from pg_class where relname='t1');
pg_table_size | pg_relation_size | ?column?
---------------+------------------+-------------
57344 | 57344 | 16438:16845
(1 row)
postgres=# commit;
COMMIT
postgres=# select pg_table_size('t1'),pg_relation_size('t1'),(select oid||':'||relfilenode from pg_class where relname='t1');
pg_table_size | pg_relation_size | ?column?
---------------+------------------+-------------
57344 | 57344 | 16438:16845
(1 row)