#插入1000W数据
postgres=# insert into t select id,id from generate_series(1,10000000) as id;
INSERT 0 10000000
 
#表膨胀系数为0.097
postgres=# select *, 1.0 - tuple_len::numeric / table_len as bloat from pgstattuple('t');
 table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent |   bloat   
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------+------------------------
 442818560 | 10000001 | 400000040 |   90.33 |    0 |    0 |     0 | 1304976 |   0.29 | 0.09669540499838127833
(1 row)
 
#占用54055个page
postgres=# select * from pg_relpages('t');
 pg_relpages 
-------------
  54055
(1 row)
 
#删除数据
postgres=# delete from t where id<>10000000;
DELETE 9999999
 
#仍然占用54055个page
postgres=# select * from pg_relpages('t');
 pg_relpages 
-------------
  54055
(1 row)
 
#膨胀率已经为0.999999
postgres=# select *, 1.0 - tuple_len::numeric / table_len as bloat from pgstattuple('t');
 table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent |   bloat   
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------+----------------------------
 442818560 |   2 |  80 |    0 |   9999999 |  399999960 |    90.33 | 1304976 |   0.29 | 0.999999819339099065766349
 
#vacuum表
postgres=# vacuum (verbose,full,analyze) t;
INFO: vacuuming "public.t"
INFO: "t": found 5372225 removable, 2 nonremovable row versions in 54055 pages
DETAIL: 0 dead row versions cannot be removed yet.
CPU: user: 0.89 s, system: 0.00 s, elapsed: 0.89 s.
INFO: analyzing "public.t"
INFO: "t": scanned 1 of 1 pages, containing 2 live rows and 0 dead rows; 2 rows in sample, 2 estimated total rows
VACUUM

create index concurrently idx_tbl_2 on tbl(id);
drop index idx_tbl_1;

create unique index concurrently user_info_username_key_1 on user_info(username);
begin;
alter table user_info drop constraint user_info_username_key;
alter table user_info add constraint user_info_username_key unique using index user_info_username_key_1;
end;

create unique index concurrently user_info_pkey_1 on user_info(id);
begin;
alter table user_info drop constraint user_info_pkey;
alter table user_info add constraint user_info_pkey primary key using index user_info_pkey_1;
end;