postgres=# create table t (id int);
CREATE TABLE
postgres=# insert into t values (1);
INSERT 0 1
postgres=# begin isolation level read committed;
BEGIN
postgres=# select *, pg_backend_pid() from t;
 id | pg_backend_pid 
----+----------------
  1 |           3876
(1 row)

postgres=# select state from pg_stat_activity where pid =3876;
        state        
---------------------
 idle in transaction
(1 row)

postgres=# delete from t where id = 1;
DELETE 1
postgres=# vacuum verbose t;
INFO:  vacuuming "public.t"
INFO:  "t": removed 1 row versions in 1 pages
INFO:  "t": found 1 removable, 0 nonremovable row versions in 1 out of 1 pages
DETAIL:  0 dead row versions cannot be removed yet, oldest xmin: 122792
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins, 0 frozen pages.
0 pages are entirely empty.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  "t": stopping truncate due to conflicting lock request
VACUUM

postgres=# begin;
BEGIN
postgres=# select pg_backend_pid();
 pg_backend_pid 
----------------
          11257

postgres=# select state from pg_stat_activity where pid = 11257;
        state        
---------------------
 idle in transaction

postgres=# select1;
ERROR:  syntax error at or near "select1"
LINE 1: select1;
        ^

postgres=# select state from pg_stat_activity where pid = 11257;
             state             
-------------------------------
 idle in transaction (aborted)

postgres=# select 1 as id into t;
SELECT 1
postgres=# begin isolation level read committed ;
BEGIN
postgres=# select txid_current();
 txid_current 
--------------
        122853 

postgres=# delete from t;
DELETE 1
postgres=# vacuum verbose t;
INFO:  vacuuming "public.t"
INFO:  "t": found 0 removable, 1 nonremovable row versions in 1 out of 1 pages
 DETAIL:  1 dead row versions cannot be removed yet, oldest xmin: 122853 
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins, 0 frozen pages.
0 pages are entirely empty.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
VACUUM