begin;

values ('for share'), ('') order by random() limit 1 \gset

select id from t where id=3 :column1 ;
select pg_sleep(random());
update t set x=x+1 where id=3;

select random() > .5 as commit \gset

\if :commit
   commit;
\else
   rollback;
\endif

vacuum freeze t;
select ctid, xmin, xmax, id, x from t;